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CYCLOSTORM
Updated: Sat 31 Oct 2020 19:59 GMT
CLICK ON STORM SYMBOL OR NAME TO ACCESS STORM DETAILS
Situation Map
GONI (West Pacific)
ATSANI (West Pacific)
Super Typhoon GONI Tropical Depression ATSANI Situation Map
Super Typhoon GONI Forecast Graphic
Super Typhoon GONI Forecast Track (Joint Typhoon Warning Center)
Super Typhoon GONI Storm-Centered Infrared
Super Typhoon GONI Storm-Centered Enhanced Infrared
Super Typhoon GONI Storm-Centered Visible
Super Typhoon GONI Warning Text (JTWC)
WTPN31 PGTW 312100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/ SUPER TYPHOON 22W (GONI) WARNING NR 016//
RMKS/
1. SUPER TYPHOON 22W (GONI) WARNING NR 016    
   02 ACTIVE TROPICAL CYCLONES IN NORTHWESTPAC
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
   WIND RADII VALID OVER OPEN WATER ONLY
    ---
   WARNING POSITION:
   311800Z --- NEAR 13.7N 125.1E
     MOVEMENT PAST SIX HOURS - 250 DEGREES AT 14 KTS
     POSITION ACCURATE TO WITHIN 010 NM
     POSITION BASED ON EYE FIXED BY A COMBINATION OF 
     SATELLITE AND RADAR
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 170 KT, GUSTS 205 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 064 KT WINDS - 040 NM NORTHEAST QUADRANT
                            035 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            050 NM NORTHWEST QUADRANT
   RADIUS OF 050 KT WINDS - 060 NM NORTHEAST QUADRANT
                            060 NM SOUTHEAST QUADRANT
                            045 NM SOUTHWEST QUADRANT
                            070 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 090 NM NORTHEAST QUADRANT
                            080 NM SOUTHEAST QUADRANT
                            070 NM SOUTHWEST QUADRANT
                            110 NM NORTHWEST QUADRANT
   REPEAT POSIT: 13.7N 125.1E
    ---
   FORECASTS:
   12 HRS, VALID AT:
   010600Z --- 13.7N 122.2E
   MAX SUSTAINED WINDS - 115 KT, GUSTS 140 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 064 KT WINDS - 020 NM NORTHEAST QUADRANT
                            020 NM SOUTHEAST QUADRANT
                            010 NM SOUTHWEST QUADRANT
                            020 NM NORTHWEST QUADRANT
   RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT
                            030 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            040 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 100 NM NORTHEAST QUADRANT
                            070 NM SOUTHEAST QUADRANT
                            060 NM SOUTHWEST QUADRANT
                            120 NM NORTHWEST QUADRANT
   VECTOR TO 24 HR POSIT: 285 DEG/ 13 KTS
    ---
   24 HRS, VALID AT:
   011800Z --- 14.3N 119.5E
   MAX SUSTAINED WINDS - 075 KT, GUSTS 090 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 064 KT WINDS - 020 NM NORTHEAST QUADRANT
                            020 NM SOUTHEAST QUADRANT
                            015 NM SOUTHWEST QUADRANT
                            020 NM NORTHWEST QUADRANT
   RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT
                            040 NM SOUTHEAST QUADRANT
                            025 NM SOUTHWEST QUADRANT
                            040 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 090 NM NORTHEAST QUADRANT
                            050 NM SOUTHEAST QUADRANT
                            030 NM SOUTHWEST QUADRANT
                            080 NM NORTHWEST QUADRANT
   VECTOR TO 36 HR POSIT: 280 DEG/ 11 KTS
    ---
   36 HRS, VALID AT:
   020600Z --- 14.6N 117.2E
   MAX SUSTAINED WINDS - 065 KT, GUSTS 080 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 064 KT WINDS - 025 NM NORTHEAST QUADRANT
                            020 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            030 NM NORTHWEST QUADRANT
   RADIUS OF 050 KT WINDS - 050 NM NORTHEAST QUADRANT
                            035 NM SOUTHEAST QUADRANT
                            030 NM SOUTHWEST QUADRANT
                            060 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 080 NM NORTHEAST QUADRANT
                            050 NM SOUTHEAST QUADRANT
                            050 NM SOUTHWEST QUADRANT
                            100 NM NORTHWEST QUADRANT
   VECTOR TO 48 HR POSIT: 275 DEG/ 10 KTS
    ---
   EXTENDED OUTLOOK:
   48 HRS, VALID AT:
   021800Z --- 14.7N 115.2E
   MAX SUSTAINED WINDS - 060 KT, GUSTS 075 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT
                            030 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            040 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 080 NM NORTHEAST QUADRANT
                            040 NM SOUTHEAST QUADRANT
                            050 NM SOUTHWEST QUADRANT
                            100 NM NORTHWEST QUADRANT
   VECTOR TO 72 HR POSIT: 270 DEG/ 07 KTS
    ---
   72 HRS, VALID AT:
   031800Z --- 14.6N 112.3E
   MAX SUSTAINED WINDS - 060 KT, GUSTS 075 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 050 KT WINDS - 030 NM NORTHEAST QUADRANT
                            025 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            020 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 090 NM NORTHEAST QUADRANT
                            030 NM SOUTHEAST QUADRANT
                            060 NM SOUTHWEST QUADRANT
                            090 NM NORTHWEST QUADRANT
   VECTOR TO 96 HR POSIT: 265 DEG/ 06 KTS
    ---
   LONG RANGE OUTLOOK:
    ---
   96 HRS, VALID AT:
   041800Z --- 14.4N 109.9E
   MAX SUSTAINED WINDS - 055 KT, GUSTS 070 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 050 KT WINDS - 020 NM NORTHEAST QUADRANT
                            015 NM SOUTHEAST QUADRANT
                            010 NM SOUTHWEST QUADRANT
                            020 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 080 NM NORTHEAST QUADRANT
                            020 NM SOUTHEAST QUADRANT
                            060 NM SOUTHWEST QUADRANT
                            080 NM NORTHWEST QUADRANT
   VECTOR TO 120 HR POSIT: 260 DEG/ 06 KTS
    ---
   120 HRS, VALID AT:
   051800Z --- 14.0N 107.5E
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
    ---
REMARKS:
312100Z POSITION NEAR 13.7N 124.4E.
31OCT20. SUPER TYPHOON 22W (GONI), LOCATED APPROXIMATELY 
245 NM EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED 
WEST-SOUTHWESTWARD AT 14 KNOTS OVER THE PAST SIX HOURS.
MAXIMUM SIGNIFICANT WAVE HEIGHT AT 311800Z IS 63 FEET. 
NEXT WARNINGS AT 010300Z, 010900Z, 011500Z AND 012100Z.
REFER TO TROPICAL DEPRESSION 23W (ATSANI) WARNINGS 
(WTPN32 PGTW) FOR SIX-HOURLY UPDATES.//
NNNN
Super Typhoon GONI Prognostic Reasoning (JTWC)
WDPN31 PGTW 311500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 22W (GONI) 
WARNING NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 22W (GONI), LOCATED APPROXIMATELY 321 NM
EAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-SOUTHWESTWARD AT 12 
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
SATELLITE IMAGERY (EIR) SHOWS A COMPACT, DENSE, AND SYMMETRICAL 
SYSTEM WITH FEEDER BANDS TIGHTLY WRAPPED AND TUCKED INTO THE 
CENTRAL CONVECTION THAT HAS MAINTAINED A 9-NM SHARPLY-OUTLINED 
EYE. OUTSIDE THE PINHOLE EYE IS A CLOUD-FREE MOAT THAT SEPARATES 
IT FROM AN EVOLVING 35-NM SECONDARY OUTER EYEWALL, PRELUDE TO AN 
EYEWALL REPLACEMENT CYCLE (ERC). THE INITIAL POSITION IS PLACED 
WITH HIGH CONFIDENCE BASED ON THE EYE IN THE EIR LOOP THAT 
PERFECTLY LINED UP WITH A WELL-DEFINED MICROWAVE EYE FEATURE 
IN THE 311000Z SSMIS 37GHZ IMAGE. A CORRESPONDING 31100Z IRBD 
IMAGE STACKS VERTICALLY WITH THE MICROWAVE EYE, INDICATING ZERO 
TILT AND LIGHT VERTICAL WIND SHEAR (VWS). THE INITIAL INTENSITY OF 
155 KTS IS BASED ON HIGH END OF 311140Z ADT ESTIMATE OF 152KTS AND 
CONGRUENT PGTW/RJTD DVORAK CURRENT INTENSITY ESTIMATES OF 
T7.5/155KTS. UPPER LEVEL ANALYSIS INDICATES A VERY FAVORABLE 
ENVIRONMENT WITH LOW (05-10KT) VWS AND ROBUST RADIAL OUTFLOW. 
ADDITIONALLY, SEA SURFACE TEMPERATURES IN THE PHILIPPINE SEA AT 
30-31C ARE VERY CONDUCIVE. THE CYCLONE IS TRACKING ALONG THE 
SOUTHERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO 
THE NORTHWEST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. THE STR WILL SLIGHTLY WEAKEN AND DRIVE STY 22W ON A FLATTER 
WESTWARD TRAJECTORY, MAKE LANDFALL OVER CENTRAL LUZON JUST AROUND 
TAU 12, TRACK JUST SOUTH OF MANILA, AND EXIT INTO THE SOUTH CHINA 
SEA (SCS) BY TAU 30. THE ENVIRONMENT WILL REMAIN FAVORABLE IN THE 
NEAR TERM. HOWEVER, THE ANTICIPATED ERC WILL CAUSE A SLIGHT AND 
GRADUAL WEAKENING TO 135KTS BY TAU 12, ALBEIT STILL AT SUPER 
TYPHOON INTENSITY. AFTERWARD, INTERACTION WITH THE RUGGED TERRAIN 
WILL CAUSE SIGNIFICANT DECAY AND WEAKEN THE SYSTEM TO 75KTS BY TAU 
36 AFTER IT EXITS INTO THE SCS. AFTER TAU 36, STY 22W WILL STEADILY 
WEAKEN TO 55KTS BY TAU 72 DUE TO INCREASED VWS (20-25KTS). 
NUMERICAL MODELS REMAIN IN TIGHT AGREEMENT, LENDING HIGH CONFIDENCE 
IN THIS PORTION OF THE JTWC FORECAST TRACK THAT IS LAID NEAR THE 
MULTI-MODEL CONSENSUS.
   C. BEYOND TAU 72, STY GONI WILL CONTINUE WESTWARD UNDER THE 
SAME STR, MAKING A SECONDARY AND FINAL LANDFALL OVER CENTRAL 
VIETNAM SOUTH OF DA NANG AROUND TAU 108. THE SYSTEM WILL CONTINUE 
TO GRADUALLY WEAKEN DUE TO THE MODERATE (20-25KT) VWS, AND AFTER 
LANDFALL, RAPID WEAKENING WITH THE ADDITION OF FRICTIONAL EFFECTS 
FROM THE TERRAIN. BY TAU 120, THE SYSTEM WILL BE REDUCED TO 35KTS. 
NAVGEM DIVERGES TO THE RIGHT OF THE MAIN CLUSTER OF NUMERICAL 
MODELS AND JGSM TO THE LEFT, THEREBY OFFSETTING EACH OTHER. IN 
VIEW OF THIS, THERE IS HIGH CONFIDENCE IN THE EXTENDED PORTION OF 
THE JTWC TRACK FORECAST THAT IS LAID IN THE MIDDLE OF THE MAIN
CLUSTER.//
NNNN
Super Typhoon GONI JMV 3.0 Data (JTWC)
WTPN51 PGTW 312100    
WARNING    ATCG MIL 22W NWP 201031192123
2020103118 22W GONI       016  02 250 14 SATL RADR 010
T000 137N 1251E 170 R064 040 NE QD 035 SE QD 020 SW QD 050 NW QD R050 060 NE QD 060 SE QD 045 SW QD 070 NW QD R034 090 NE QD 080 SE QD 070 SW QD 110 NW QD 
T012 137N 1222E 115 R064 020 NE QD 020 SE QD 010 SW QD 020 NW QD R050 040 NE QD 030 SE QD 020 SW QD 040 NW QD R034 100 NE QD 070 SE QD 060 SW QD 120 NW QD 
T024 143N 1195E 075 R064 020 NE QD 020 SE QD 015 SW QD 020 NW QD R050 040 NE QD 040 SE QD 025 SW QD 040 NW QD R034 090 NE QD 050 SE QD 030 SW QD 080 NW QD 
T036 146N 1172E 065 R064 025 NE QD 020 SE QD 020 SW QD 030 NW QD R050 050 NE QD 035 SE QD 030 SW QD 060 NW QD R034 080 NE QD 050 SE QD 050 SW QD 100 NW QD 
T048 147N 1152E 060 R050 040 NE QD 030 SE QD 020 SW QD 040 NW QD R034 080 NE QD 040 SE QD 050 SW QD 100 NW QD 
T072 146N 1123E 060 R050 030 NE QD 025 SE QD 020 SW QD 020 NW QD R034 090 NE QD 030 SE QD 060 SW QD 090 NW QD 
T096 144N 1099E 055 R050 020 NE QD 015 SE QD 010 SW QD 020 NW QD R034 080 NE QD 020 SE QD 060 SW QD 080 NW QD 
T120 140N 1075E 035 
AMP
    120HR DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
SUBJ:  SUPER TYPHOON 22W (GONI) WARNING NR 016    
1. SUPER TYPHOON 22W (GONI) WARNING NR 016    
   02 ACTIVE TROPICAL CYCLONES IN NORTHWESTPAC
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
   WIND RADII VALID OVER OPEN WATER ONLY
    ---
   WARNING POSITION:
   311800Z --- NEAR 13.7N 125.1E
     MOVEMENT PAST SIX HOURS - 250 DEGREES AT 14 KTS
     POSITION ACCURATE TO WITHIN 010 NM
     POSITION BASED ON EYE FIXED BY A COMBINATION OF 
     SATELLITE AND RADAR
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 170 KT, GUSTS 205 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 064 KT WINDS - 040 NM NORTHEAST QUADRANT
                            035 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            050 NM NORTHWEST QUADRANT
   RADIUS OF 050 KT WINDS - 060 NM NORTHEAST QUADRANT
                            060 NM SOUTHEAST QUADRANT
                            045 NM SOUTHWEST QUADRANT
                            070 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 090 NM NORTHEAST QUADRANT
                            080 NM SOUTHEAST QUADRANT
                            070 NM SOUTHWEST QUADRANT
                            110 NM NORTHWEST QUADRANT
   REPEAT POSIT: 13.7N 125.1E
    ---
   FORECASTS:
   12 HRS, VALID AT:
   010600Z --- 13.7N 122.2E
   MAX SUSTAINED WINDS - 115 KT, GUSTS 140 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 064 KT WINDS - 020 NM NORTHEAST QUADRANT
                            020 NM SOUTHEAST QUADRANT
                            010 NM SOUTHWEST QUADRANT
                            020 NM NORTHWEST QUADRANT
   RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT
                            030 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            040 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 100 NM NORTHEAST QUADRANT
                            070 NM SOUTHEAST QUADRANT
                            060 NM SOUTHWEST QUADRANT
                            120 NM NORTHWEST QUADRANT
   VECTOR TO 24 HR POSIT: 285 DEG/ 13 KTS
    ---
   24 HRS, VALID AT:
   011800Z --- 14.3N 119.5E
   MAX SUSTAINED WINDS - 075 KT, GUSTS 090 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 064 KT WINDS - 020 NM NORTHEAST QUADRANT
                            020 NM SOUTHEAST QUADRANT
                            015 NM SOUTHWEST QUADRANT
                            020 NM NORTHWEST QUADRANT
   RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT
                            040 NM SOUTHEAST QUADRANT
                            025 NM SOUTHWEST QUADRANT
                            040 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 090 NM NORTHEAST QUADRANT
                            050 NM SOUTHEAST QUADRANT
                            030 NM SOUTHWEST QUADRANT
                            080 NM NORTHWEST QUADRANT
   VECTOR TO 36 HR POSIT: 280 DEG/ 11 KTS
    ---
   36 HRS, VALID AT:
   020600Z --- 14.6N 117.2E
   MAX SUSTAINED WINDS - 065 KT, GUSTS 080 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 064 KT WINDS - 025 NM NORTHEAST QUADRANT
                            020 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            030 NM NORTHWEST QUADRANT
   RADIUS OF 050 KT WINDS - 050 NM NORTHEAST QUADRANT
                            035 NM SOUTHEAST QUADRANT
                            030 NM SOUTHWEST QUADRANT
                            060 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 080 NM NORTHEAST QUADRANT
                            050 NM SOUTHEAST QUADRANT
                            050 NM SOUTHWEST QUADRANT
                            100 NM NORTHWEST QUADRANT
   VECTOR TO 48 HR POSIT: 275 DEG/ 10 KTS
    ---
   EXTENDED OUTLOOK:
   48 HRS, VALID AT:
   021800Z --- 14.7N 115.2E
   MAX SUSTAINED WINDS - 060 KT, GUSTS 075 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT
                            030 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            040 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 080 NM NORTHEAST QUADRANT
                            040 NM SOUTHEAST QUADRANT
                            050 NM SOUTHWEST QUADRANT
                            100 NM NORTHWEST QUADRANT
   VECTOR TO 72 HR POSIT: 270 DEG/ 07 KTS
    ---
   72 HRS, VALID AT:
   031800Z --- 14.6N 112.3E
   MAX SUSTAINED WINDS - 060 KT, GUSTS 075 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 050 KT WINDS - 030 NM NORTHEAST QUADRANT
                            025 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            020 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 090 NM NORTHEAST QUADRANT
                            030 NM SOUTHEAST QUADRANT
                            060 NM SOUTHWEST QUADRANT
                            090 NM NORTHWEST QUADRANT
   VECTOR TO 96 HR POSIT: 265 DEG/ 06 KTS
    ---
   LONG RANGE OUTLOOK:
    ---
   96 HRS, VALID AT:
   041800Z --- 14.4N 109.9E
   MAX SUSTAINED WINDS - 055 KT, GUSTS 070 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 050 KT WINDS - 020 NM NORTHEAST QUADRANT
                            015 NM SOUTHEAST QUADRANT
                            010 NM SOUTHWEST QUADRANT
                            020 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 080 NM NORTHEAST QUADRANT
                            020 NM SOUTHEAST QUADRANT
                            060 NM SOUTHWEST QUADRANT
                            080 NM NORTHWEST QUADRANT
   VECTOR TO 120 HR POSIT: 260 DEG/ 06 KTS
    ---
   120 HRS, VALID AT:
   051800Z --- 14.0N 107.5E
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
    ---
REMARKS:
312100Z POSITION NEAR 13.7N 124.4E.
31OCT20. SUPER TYPHOON 22W (GONI), LOCATED APPROXIMATELY 245 NM
EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-
SOUTHWESTWARD AT 14 KNOTS OVER THE PAST SIX HOURS.
MAXIMUM SIGNIFICANT WAVE HEIGHT AT 311800Z IS 63 FEET. NEXT
WARNINGS AT 010300Z, 010900Z, 011500Z AND 012100Z.
FOR SIX-HOURLY UPDATES.
//
2220102506 112N1444E  15
2220102512 114N1436E  15
2220102518 117N1431E  15
2220102600 124N1427E  15
2220102606 134N1424E  15
2220102612 145N1420E  20
2220102618 150N1418E  20
2220102700 154N1418E  20
2220102706 158N1414E  20
2220102712 163N1410E  20
2220102718 165N1407E  20
2220102800 166N1401E  25
2220102806 166N1395E  30
2220102812 166N1385E  35
2220102818 166N1376E  45
2220102900 166N1367E  55
2220102900 166N1367E  55
2220102906 168N1357E  70
2220102906 168N1357E  70
2220102906 168N1357E  70
2220102912 166N1345E  90
2220102912 166N1345E  90
2220102912 166N1345E  90
2220102918 164N1334E 120
2220102918 164N1334E 120
2220102918 164N1334E 120
2220103000 164N1327E 130
2220103000 164N1327E 130
2220103000 164N1327E 130
2220103006 163N1316E 150
2220103006 163N1316E 150
2220103006 163N1316E 150
2220103012 161N1309E 155
2220103012 161N1309E 155
2220103012 161N1309E 155
2220103018 158N1299E 155
2220103018 158N1299E 155
2220103018 158N1299E 155
2220103100 153N1288E 160
2220103100 153N1288E 160
2220103100 153N1288E 160
2220103106 147N1276E 155
2220103106 147N1276E 155
2220103106 147N1276E 155
2220103112 142N1265E 155
2220103112 142N1265E 155
2220103112 142N1265E 155
2220103118 137N1251E 170
2220103118 137N1251E 170
2220103118 137N1251E 170
NNNN

Satellite Imagery

Satellite Animations

Tropical Depression ATSANI Forecast Graphic
Tropical Depression ATSANI Forecast Track (Joint Typhoon Warning Center)
Tropical Depression ATSANI Storm-Centered Infrared
Tropical Depression ATSANI Storm-Centered Enhanced Infrared
Tropical Depression ATSANI Storm-Centered Visible
Tropical Depression ATSANI Warning Text (JTWC)
WTPN32 PGTW 311500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL DEPRESSION 23W (ATSANI) WARNING NR 009//
RMKS/
1. TROPICAL DEPRESSION 23W (ATSANI) WARNING NR 009    
   02 ACTIVE TROPICAL CYCLONES IN NORTHWESTPAC
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
   WIND RADII VALID OVER OPEN WATER ONLY
    ---
   WARNING POSITION:
   311200Z --- NEAR 14.7N 137.6E
     MOVEMENT PAST SIX HOURS - 295 DEGREES AT 12 KTS
     POSITION ACCURATE TO WITHIN 025 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   REPEAT POSIT: 14.7N 137.6E
    ---
   FORECASTS:
   12 HRS, VALID AT:
   010000Z --- 16.2N 135.2E
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 034 KT WINDS - 030 NM NORTHEAST QUADRANT
                            000 NM SOUTHEAST QUADRANT
                            015 NM SOUTHWEST QUADRANT
                            035 NM NORTHWEST QUADRANT
   VECTOR TO 24 HR POSIT: 300 DEG/ 13 KTS
    ---
   24 HRS, VALID AT:
   011200Z --- 17.4N 132.8E
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 034 KT WINDS - 070 NM NORTHEAST QUADRANT
                            090 NM SOUTHEAST QUADRANT
                            030 NM SOUTHWEST QUADRANT
                            000 NM NORTHWEST QUADRANT
   VECTOR TO 36 HR POSIT: 300 DEG/ 10 KTS
    ---
   36 HRS, VALID AT:
   020000Z --- 18.4N 131.0E
   MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 034 KT WINDS - 070 NM NORTHEAST QUADRANT
                            140 NM SOUTHEAST QUADRANT
                            040 NM SOUTHWEST QUADRANT
                            030 NM NORTHWEST QUADRANT
   VECTOR TO 48 HR POSIT: 305 DEG/ 04 KTS
    ---
   EXTENDED OUTLOOK:
   48 HRS, VALID AT:
   021200Z --- 18.9N 130.3E
   MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 034 KT WINDS - 100 NM NORTHEAST QUADRANT
                            090 NM SOUTHEAST QUADRANT
                            090 NM SOUTHWEST QUADRANT
                            080 NM NORTHWEST QUADRANT
   VECTOR TO 72 HR POSIT: 325 DEG/ 02 KTS
    ---
   72 HRS, VALID AT:
   031200Z --- 19.4N 129.9E
   MAX SUSTAINED WINDS - 055 KT, GUSTS 070 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT
                            040 NM SOUTHEAST QUADRANT
                            040 NM SOUTHWEST QUADRANT
                            040 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 120 NM NORTHEAST QUADRANT
                            100 NM SOUTHEAST QUADRANT
                            090 NM SOUTHWEST QUADRANT
                            100 NM NORTHWEST QUADRANT
   VECTOR TO 96 HR POSIT: 250 DEG/ 03 KTS
    ---
   LONG RANGE OUTLOOK:
    ---
   96 HRS, VALID AT:
   041200Z --- 19.0N 128.7E
   MAX SUSTAINED WINDS - 070 KT, GUSTS 085 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 064 KT WINDS - 010 NM NORTHEAST QUADRANT
                            020 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            020 NM NORTHWEST QUADRANT
   RADIUS OF 050 KT WINDS - 030 NM NORTHEAST QUADRANT
                            040 NM SOUTHEAST QUADRANT
                            030 NM SOUTHWEST QUADRANT
                            030 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 120 NM NORTHEAST QUADRANT
                            050 NM SOUTHEAST QUADRANT
                            050 NM SOUTHWEST QUADRANT
                            120 NM NORTHWEST QUADRANT
   VECTOR TO 120 HR POSIT: 265 DEG/ 09 KTS
    ---
   120 HRS, VALID AT:
   051200Z --- 18.8N 124.9E
   MAX SUSTAINED WINDS - 080 KT, GUSTS 100 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 064 KT WINDS - 020 NM NORTHEAST QUADRANT
                            010 NM SOUTHEAST QUADRANT
                            010 NM SOUTHWEST QUADRANT
                            020 NM NORTHWEST QUADRANT
   RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT
                            030 NM SOUTHEAST QUADRANT
                            030 NM SOUTHWEST QUADRANT
                            050 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 120 NM NORTHEAST QUADRANT
                            060 NM SOUTHEAST QUADRANT
                            060 NM SOUTHWEST QUADRANT
                            130 NM NORTHWEST QUADRANT
    ---
REMARKS:
311500Z POSITION NEAR 15.1N 137.0E.
31OCT20. TROPICAL DEPRESSION 23W (ATSANI), LOCATED APPROXIMATELY 963 
NM EAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 12 
KNOTS OVER THE PAST SIX HOURS. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 
311200Z IS 12 FEET. NEXT WARNINGS AT 312100Z, 010300Z, 010900Z AND 
011500Z. REFER TO SUPER TYPHOON 22W (GONI) WARNINGS (WTPN31 PGTW)
FOR SIX-HOURLY UPDATES.//
NNNN
Tropical Depression ATSANI Prognostic Reasoning (JTWC)
WDPN32 PGTW 311500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (ATSANI) 
WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 23W (ATSANI), LOCATED APPROXIMATELY 963 NM 
EAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 12 
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) 
SATELLITE IMAGERY SHOWS A WEAK AND DISORGANIZED SYSTEM WITH FLARING 
CENTRAL CONVECTION. THE INITIAL POSITION IS PLACED WITH LOW 
CONFIDENCE BASED ON A NOTCH FEATURE IN THE EIR LOOP. THE INITIAL 
INTENSITY IS BASED ON PGTW AND RJTD DVORAK ESTIMATES OF T2.0/30KTS. 
THE ENVIRONMENT IS OVERALL UNFAVORABLE WITH MODERATE TO HIGH 
(20-25KT) VERTICAL WIND SHEAR (VWS) AND WEAK OUTFLOW ALOFT OFFSET 
ONLY SLIGHTLY BY WARM (30-31C) SEA SURFACE TEMPERATURES (SST). THE 
CYCLONE IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP-
LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS A NOTABLE CHANGE IN THE FORECAST TRACK PHILOSOPHY. 
THE MID-PORTION OF THE FORECAST HAS BEEN SLOWED SIGNIFICANTLY TO 
REFLECT A QUASI-STATIONARY MOTION IN THE COL ZONE BETWEEN TWO 
RIDGES SPLIT BY A TRANSITORY MIDLATITUDE TROUGH. THE INTENSITIES 
IN THE EXTENDED PORTION OF THE FORECAST HAVE ALSO BEEN GREATLY 
REDUCED.
   B. TD 23W WILL CONTINUE ON ITS CURRENT TRACK IN THE PHILIPPINE 
SEA UNDER THE SAME STR. AFTER TAU 36, A SHORTWAVE MIDLATITUDE 
TROUGH APPROACHING FROM THE NORTHWEST WILL ERODE AND SPLIT THE STR 
AND PULL THE CYCLONE POLEWARD INTO THE COL ZONE BETWEEN THE 
RIDGES. THE ENVIRONMENT IS FORECAST TO IMPROVE SLIGHTLY AS VWS 
WEAKENS IN THE COL ZONE AND POLEWARD OUTFLOW IMPROVES, LEADING TO 
A SLOW INTENSIFICATION TO 55KTS BY TAU 72. NUMERICAL MODELS ARE 
IN FAIR AGREEMENT UP TO TAU 36. AFTERWARD, NAVGEM DIVERGES TO THE 
RIGHT OF THE MODEL ENVELOPE. THERE IS FAIR CONFIDENCE IN THIS 
PORTION OF THE JTWC TRACK FORECAST WHICH IS PLACED SLIGHTLY LEFT 
OF THE MULTI-MODEL CONSENSUS TO OFFSET THE UNLIKELY NAVGEM SOLUTION 
DRIVING THE VORTEX INTO THE STR. 
   C. IN THE EXTENDED FORECAST, THE SECONDARY STR BEHIND THE 
SHORTWAVE TROUGH WILL ASSUME STEERING AND SLOWLY DRIVE TD 23W WEST-
SOUTHWESTWARD THEN WESTWARD. ENVIRONMENTAL CONDITIONS ARE FORECAST 
TO IMPROVE EVEN MORE WITH DECREASED VWS (10-15KTS) AND THE ADDITION 
OF AN EQUATORWARD OUTFLOW CHANNEL. THESE CONDITIONS, COUPLED WITH 
CONTINUED WARM SST, WILL ALLOW FOR FURTHER INTENSIFICATION TO 80KTS 
BY TAU 120. NUMERICAL MODELS SIGNIFICANTLY DIVERGE TO OVER 400NM BY 
TAU 120 WITH VARYING TRACK SPEEDS, LENDING POOR CONFIDENCE IN THE 
EXTENDED PORTION OF THE JTWC FORECAST TRACK.//
NNNN
Tropical Depression ATSANI JMV 3.0 Data (JTWC)
WTPN52 PGTW 311500    
WARNING    ATCG MIL 23W NWP 201031131605
2020103112 23W ATSANI     009  02 295 12 SATL 025
T000 147N 1376E 030 
T012 162N 1352E 035 R034 030 NE QD 000 SE QD 015 SW QD 035 NW QD 
T024 174N 1328E 035 R034 070 NE QD 090 SE QD 030 SW QD 000 NW QD 
T036 184N 1310E 040 R034 070 NE QD 140 SE QD 040 SW QD 030 NW QD 
T048 189N 1303E 045 R034 100 NE QD 090 SE QD 090 SW QD 080 NW QD 
T072 194N 1299E 055 R050 040 NE QD 040 SE QD 040 SW QD 040 NW QD R034 120 NE QD 100 SE QD 090 SW QD 100 NW QD 
T096 190N 1287E 070 R064 010 NE QD 020 SE QD 020 SW QD 020 NW QD R050 030 NE QD 040 SE QD 030 SW QD 030 NW QD R034 120 NE QD 050 SE QD 050 SW QD 120 NW QD 
T120 188N 1249E 080 R064 020 NE QD 010 SE QD 010 SW QD 020 NW QD R050 040 NE QD 030 SE QD 030 SW QD 050 NW QD R034 120 NE QD 060 SE QD 060 SW QD 130 NW QD 
AMP
SUBJ:  TROPICAL DEPRESSION 23W (ATSANI) WARNING NR 009    
1. TROPICAL DEPRESSION 23W (ATSANI) WARNING NR 009    
   02 ACTIVE TROPICAL CYCLONES IN NORTHWESTPAC
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
   WIND RADII VALID OVER OPEN WATER ONLY
    ---
   WARNING POSITION:
   311200Z --- NEAR 14.7N 137.6E
     MOVEMENT PAST SIX HOURS - 295 DEGREES AT 12 KTS
     POSITION ACCURATE TO WITHIN 025 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   REPEAT POSIT: 14.7N 137.6E
    ---
   FORECASTS:
   12 HRS, VALID AT:
   010000Z --- 16.2N 135.2E
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 034 KT WINDS - 030 NM NORTHEAST QUADRANT
                            000 NM SOUTHEAST QUADRANT
                            015 NM SOUTHWEST QUADRANT
                            035 NM NORTHWEST QUADRANT
   VECTOR TO 24 HR POSIT: 300 DEG/ 13 KTS
    ---
   24 HRS, VALID AT:
   011200Z --- 17.4N 132.8E
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 034 KT WINDS - 070 NM NORTHEAST QUADRANT
                            090 NM SOUTHEAST QUADRANT
                            030 NM SOUTHWEST QUADRANT
                            000 NM NORTHWEST QUADRANT
   VECTOR TO 36 HR POSIT: 300 DEG/ 10 KTS
    ---
   36 HRS, VALID AT:
   020000Z --- 18.4N 131.0E
   MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 034 KT WINDS - 070 NM NORTHEAST QUADRANT
                            140 NM SOUTHEAST QUADRANT
                            040 NM SOUTHWEST QUADRANT
                            030 NM NORTHWEST QUADRANT
   VECTOR TO 48 HR POSIT: 305 DEG/ 04 KTS
    ---
   EXTENDED OUTLOOK:
   48 HRS, VALID AT:
   021200Z --- 18.9N 130.3E
   MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 034 KT WINDS - 100 NM NORTHEAST QUADRANT
                            090 NM SOUTHEAST QUADRANT
                            090 NM SOUTHWEST QUADRANT
                            080 NM NORTHWEST QUADRANT
   VECTOR TO 72 HR POSIT: 325 DEG/ 02 KTS
    ---
   72 HRS, VALID AT:
   031200Z --- 19.4N 129.9E
   MAX SUSTAINED WINDS - 055 KT, GUSTS 070 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT
                            040 NM SOUTHEAST QUADRANT
                            040 NM SOUTHWEST QUADRANT
                            040 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 120 NM NORTHEAST QUADRANT
                            100 NM SOUTHEAST QUADRANT
                            090 NM SOUTHWEST QUADRANT
                            100 NM NORTHWEST QUADRANT
   VECTOR TO 96 HR POSIT: 250 DEG/ 03 KTS
    ---
   LONG RANGE OUTLOOK:
    ---
   96 HRS, VALID AT:
   041200Z --- 19.0N 128.7E
   MAX SUSTAINED WINDS - 070 KT, GUSTS 085 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 064 KT WINDS - 010 NM NORTHEAST QUADRANT
                            020 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            020 NM NORTHWEST QUADRANT
   RADIUS OF 050 KT WINDS - 030 NM NORTHEAST QUADRANT
                            040 NM SOUTHEAST QUADRANT
                            030 NM SOUTHWEST QUADRANT
                            030 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 120 NM NORTHEAST QUADRANT
                            050 NM SOUTHEAST QUADRANT
                            050 NM SOUTHWEST QUADRANT
                            120 NM NORTHWEST QUADRANT
   VECTOR TO 120 HR POSIT: 265 DEG/ 09 KTS
    ---
   120 HRS, VALID AT:
   051200Z --- 18.8N 124.9E
   MAX SUSTAINED WINDS - 080 KT, GUSTS 100 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 064 KT WINDS - 020 NM NORTHEAST QUADRANT
                            010 NM SOUTHEAST QUADRANT
                            010 NM SOUTHWEST QUADRANT
                            020 NM NORTHWEST QUADRANT
   RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT
                            030 NM SOUTHEAST QUADRANT
                            030 NM SOUTHWEST QUADRANT
                            050 NM NORTHWEST QUADRANT
   RADIUS OF 034 KT WINDS - 120 NM NORTHEAST QUADRANT
                            060 NM SOUTHEAST QUADRANT
                            060 NM SOUTHWEST QUADRANT
                            130 NM NORTHWEST QUADRANT
    ---
REMARKS:
311500Z POSITION NEAR 15.1N 137.0E.
31OCT20. TROPICAL DEPRESSION 23W (ATSANI), LOCATED APPROXIMATELY 963 
NM EAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 12 
KNOTS OVER THE PAST SIX HOURS. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 
311200Z IS 12 FEET. NEXT WARNINGS AT 312100Z, 010300Z, 010900Z AND 
FOR SIX-HOURLY UPDATES.//
2320102712  50N1530E  15
2320102718  54N1523E  15
2320102800  57N1517E  15
2320102806  58N1511E  15
2320102812  58N1504E  15
2320102818  58N1495E  15
2320102900  61N1488E  20
2320102906  81N1482E  20
2320102912  95N1473E  25
2320102918 103N1460E  25
2320103000 109N1446E  30
2320103006 115N1434E  25
2320103012 120N1422E  25
2320103018 124N1407E  30
2320103100 133N1397E  25
2320103106 142N1387E  30
2320103112 147N1376E  30
NNNN

Satellite Imagery

Satellite Animations

What Is a Hurricane?

A hurricane (or typhoon, or severe tropical cyclone), the strongest storm on Earth, is a cyclonic (rotary) storm that derives its energy from cloud formation and rainfall, unlike frontal cyclones that derive their power from a temperature gradient.

A hurricane begins as a tropical depression with a sustained wind speed of less than 39 mph (35 knots; 63 km/hr). As the system strengthens, it becomes a tropical storm with winds from 39 to 73 mph (35-63 knots; 63-118 km/hr). Tropical storms are named in the Atlantic, East, Central and Northwest Pacific, in the South Indian Ocean, and in the Arabian Sea. When the winds are sustained (based on a one-minute average) at 74 mph (64 knots; 119 km/hr), the storm becomes: In the Atlantic Ocean, East Pacific, Central Pacific (east of the International Dateline) and Southeast Pacific (east of 160°E) a Hurricane; in the Northwest Pacific (west of the International Dateline) a Typhoon; in the Southwest Pacific (west of 160°E) and Southeast Indian Ocean (east of 90°E) a Severe Tropical Cyclone; in the North Indian Ocean a Severe Cyclonic Storm; and in the Southwest Indian Ocean (west of 90°E) a Tropical Cyclone.

The Saffir-Simpson Hurricane Scale

Category 1 – 64-82 knots (74-95 mph; 119-153 km/h). Damage is limited to foliage, signage, unanchored boats and mobile homes. There is no significant damage to buildings. The main threat to life and property may be flooding from heavy rains.

Category 2 – 83-95 knots (96-110 mph; 154-177 km/h). Roof damage to buildings. Doors and windows damaged. Mobile homes severely damaged. Piers damaged by storm surge. Some trees blown down, more extensive limb damage.

Category 3 – 96-112 knots (111-129 mph; 178-208 km/h). This is the first step of Major Hurricane. Landfalling major hurricanes have their names retired from the list of available hurricane names. For example, after Hurricane Charley made landfall in Florida as a Category 4 hurricane, its name was retired. In the future, when someone says “Hurricane Charley”, there will be no doubt which storm is meant. Category 3 storms cause structural damage to some buildings. Mobile homes are completely destroyed. Roof damage is common. Storm surge begins to cause significant damage in beaches and harbors, with small buildings destroyed.

Category 4 – 113-136 knots (130-156 mph; 209-251 km/h). Structural failure of some buildings. Complete roof failures on many buildings. Extreme storm surge damage and flooding. Severe coastal erosion, with permanent changes to the coastal landscape not unheard of. Hurricane force winds extend well inland.

Category 5 – 137+ knots (157+ mph; 262+ km/h). Complete roof failure on most buildings. Many buildings destroyed, or structurally damaged beyond repair. Catastrophic storm surge damage. All Category 5 hurricanes’ names are retired, regardless whether they ever make landfall. In the Northwest Pacific, a typhoon that reaches 150 mph (241 km/hr) is called a Super Typhoon. The damage caused by a super typhoon is equivalent to a strong Category 4 or Category 5 hurricane, depending on how strong the typhoon is. Because conditions in the Northwest Pacific favor storm formation throughout most of the year, super typhoons are much more common than Category 5 hurricanes. Every year the Northwest Pacific sees several super typhoons, while the Atlantic might see one Category 5 every few years.

SAFFIR-SIMPSON SCALE
CategoryKnotsMPHKM/HDamage
164-8274-95119-153Minimal
283-9596-110154-177Moderate
396-112111-129178-208Extensive
4113-136130-156209-251Extreme
Super Typhoon130+150+241+Catastrophic
5137+157+262+Catastrophic

Storm Surge

Historically, storm surge is the primary killer in hurricanes. The exact storm surge in any given area will be determined by how quickly the water depth increases offshore. In deep-water enviroments, such as the Hawaiian islands, storm surge will be enhanced by the rapidly decreasing ocean depth as the wind-driven surge approaches the coast. The peak storm surge is on the right-front quadrant (left-front in the Southern Hemisphere) of the eyewall at landfall, where on-shore winds are the strongest, and at the leading edge of the eyewall. Contrary to a popular myth, the storm surge is entirely wind-driven water—it is not caused by the low pressure of the eye. Another factor in the severity of the storm surge is tide. Obviously, an 18-foot storm surge at high tide is that much worse than an 18-foot surge at low tide.

Tropical Cyclone Formation

Tropical Cyclone Genesis is the technical term for the process of storm formation that leads ultimately to what are called hurricanes, typhoons, or tropical cyclones in various parts of the world.

This occurs when, in the Northern Hemisphere, the Intertropical Convergence Zone, or ITCZ, shifts northward out of the doldrums and atmospheric conditions become favorable for tropical cyclone formation after about the middle of May.

A series of low-pressure ripples develops within the ITCZ. These are known as tropical waves and progress from east to west. In the late season, they typically shift their movement toward the west-nothwest, or even northwest, after crossing 45° or 50° W longitude.

These tropical waves, ideally embedded in the deep-layer easterly flow, contain a northeast wind shift. This is typically referred to as a “convergence”, where lines of equal atmospheric pressure are pressed together between the high-pressure ridge to the north and the developing low-pressure system. The divergence that results ahead of the convergence zone gives us a notheasterly wind as the axis of the tropical wave approaches. Gusts up to 25 mph may occur. Sometimes there can be gusts to tropical storm force in stronger waves. There can be next to no weather associated with these waves, and they may pass virtually unnoticed. More typically, there are bands of disturbed weather riding the axis of the wave.

Easterly Wave
(Graphic by Robert Simmon, NASA GSFC)

When the wave passes over warmer waters (SSTs), convection and resulting rainfall are enhanced. This greater rainfall is concomitant with falling surface pressures. By the time these pressures fall to 1008mb, it is likely that the northeast wind has closed off to a southwest wind on the backside of the wave. The forward motion of the wave completes the closure on the northern side of a broad low-level center, and a tropical depression has formed.

We often hear that a tropical depression has formed, but conditions are unfavorable for further development. There are two conditions that must be present for the tropical depression to continue its development: warm SSTs (above 79° Fahrenheit/26° Celsius) and low vertical shear. A tropical cyclone derives its power from the warm waters below. In addition, a strong anticyclone directly above the low-level inflow is favorable. As a tropical cyclone is pulling in warm, moist air at the surface, it must also evacuate this inbound flow aloft. This occurs in the upper levels of the atmosphere, where high pressure facilitates the development of the cyclone by evacuating the flow from the lower levels of the cyclone. Every powerful hurricane has an equally powerful high pressure system over it. At the surface, the air spirals inward in a counter-clockwise direction, rises in the developing center, and spirals out at the top in a clockwise direction. In the Southern Hemisphere, it is reversed: clockwise inbound, counterclockwise outbound.

If the upper-level high pressure system does not develop over our cyclone, it means there is shear instead. This is a strong jet of air that is blowing directly over the cyclone, ripping the tops off the deep convection. This has the effect of breaking down the whole mechanism. This is known as vertical shear. Vertical shear usually comes from a westerly direction, and can occur if the cyclone is located in an unfavorable position near a cold front or upper-level low pressure system. Another factor that can interfere with the development of a tropical cyclone is subsidence. Subsidence is the sinking of air. This happens on the edge of an upper-level high-pressure system. Subsiding air has the effect of suppressing thunderstorm formation. This also is why a tropical storm that tries to form near an established hurricane has a very difficult time—the cyclone is on the edge of the hurricane’s upper-level outflow, and may have to contend with both subsidence and shear. The effect of shear on a cyclone can range from a failure to thrive to catastrophic collapse of the tropical cyclone’s support structure.

Tropical cyclones have the low-level circulation and the upper-level circulation (outflow), whose formation was discussed above. There is also a mid-level circulation. The mid-level circulation is similar in structure to the low-level circulation, and is critical to the survival of a tropical cyclone that is passing over land. The lowel-level circulation can be severely disrupted, or even dissipated, by interaction with land, especially mountainous terrain. If the mid-level circulation remains intact, the cyclone can regenerate rapidly when it reemerges over water, providing other factors are favorable.

Hurricane Structure
(Image courtesy NOAA)

Assuming all the ingredients are in place—warm SSTs, upper-level high pressure, and falling surface pressures—the cyclone will develop and reach a point of rapid intensification. It is one of nature’s perfect machines. As warm waters feed the convection swirling around the center, heavy rainfall lowers surface pressures, high pressure aloft evacuates the inflow, which intensifies the inflow of warm, moist air, which in turn increases the rainfall and brings about a more rapid fall in central pressure.

Eye formation begins when a tropical storm reaches approximately 65mph, provided conditions are favorable for strengthening to continue. The eyewall begins to make its appearance, usually on the eastern (Northern Hemisphere) edge of the center. As the system becomes better organized and stronger, the center contracts from about 200 miles across to roughly 90 miles at this stage. An increase in rotational velocity accompanies the smaller, more defined center. The inflow is spiralling in ever faster as it is evacuated up through the developing eyewall and out by the high pressure outflow structure. The eye begins to appear as a clear spot in the center, as the air here is sinking. The eyewall creates subsidence that not only helps clear the eye, but can also produce a feature known as the “moat”, which is an area of relatively weak convection outside the core of the tropical cyclone. The combination of eye and moat can make the storm’s core look like a doughnut. The eye can have a diameter anywhere from 10 to 40 miles across.

Tropical cyclones can exhibit a great deal of durabilty provided that the upper level support remains and the southerly (Northern Hemisphere) inflow is present. The worst thing that can happen is for this southerly (or equatorward) inflow to get cut off. Here are some examples: In 1998, Hurricane Mitch developed into a supermassive Category 5 hurricane. Nevertheless weakening began when the center moved to a position directly north of Honduras, cutting off the southerly inflow, even though the eye was still over a hundred miles off shore. Later, Mitch maintained its mid-level core against all odds over the mountains of Central America because he was able to advect moisture from the East Pacific. Reintensification to tropical storm strength was almost immediate after reaching the Bay of Campeche. Mitch never dissipated. In 1988 Gilbert hit the Yucatan near Cancún as a Category 5 hurricane. The Yucatan peninsula, though flat, extended far enough south through the critical southerly inflow zone that Gilbert never recovered, even after moving over the open waters of the western Gulf of Mexico. Contrast this with the northern Gulf coast and numerous examples from Camille to Elena and beyond, where the proximity of the eye to land is not necessarily a weakening factor, although the relatively extensive shelf water can sometimes be an inhibiting factor, if a slow-moving storm generates enough upwelling. A recent Southern Hemisphere example of this is Severe Tropical Cyclone Monica, which developed into a “super cyclone” just north of Australia. The northerly (equatorward) inflow over the Arafura Sea fueled this system.

What are the factors that contribute to the decay of a tropical cyclone? They are Upwelling, Entraining dry air, Moving over cool waters, Exposure to upper-level westerlies, and finally Landfall.

Upwelling. When a hurricane stalls, its movement is has fallen below 5mph, or its movement is erratic over a small area, the wave action caused by the strong surface winds churns the ocean surface and produces upwelling. This has the effect of cooling the temperature of the sea surface over an area 200 to 300 miles across. The result is weakening. It is possible for a hurricane to stall in one area long enough that it dissipates. In 2004, Hurricane Frances stalled off the southeast Florida coast long enough that the core of the hurricane collapsed. Frances eventually made landfall as a Category 1 hurricane, instead of the earlier expected Category 3.

Entraining dry air. Sometimes, during the peak season, when tropical cyclones approach contintental land masses, they may entrain dry air as part of their interaction with frontal troughs that carry cool, dry air behind them. It is one of the ironies of the Atlantic Hurricane Season that, just when things get going, it’s already September and the strength and frequency of cold fronts is increasing. These fronts interfere by deflecting the hurricane or injecting dry air into the circulation, or both. The dry air kills the convective masses that drive the hurricane’s engine. If the dry air entrains deeply enough, it can cause significant weakening.

Moving over cool water. Similar to upwelling, when a tropical cyclone moves over cool water (below 77° Fahrenheit/25° Celsius), it begins to weaken. Eventually this causes dissipation, particularly in the East Pacific. In the Atlantic, if the storm is caught in the mid-latitude westerlies and begins to recurve to the northeast, it generally becomes an extratropical storm by the time it has reached about 45° W. This is the so-called “graveyard” of Atlantic hurricanes. The storm becomes extratropical when it has transitioned to a cold-core, baroclinically driven system, and eventually becomes a gale in the north Atlantic, or is absorbed by a large gale. There have been times when a hurricane passes north of the Azores and hits the British Isles as a Force 8 or stronger gale, having maintained a recognizable inner core.

Exposure to upper-level westerlies. It happens that the ridge of high pressure that keeps the hurricane heading toward the west frequently breaks down. In the Atlantic Ocean, this may result in strong upper-level westerlies diving down and impinging on the northern edge of the hurricane’s upper-level support structure. Poleward outflow is restricted. A hurricane can still thrive when outflow is restricted in one quadrant. If the forces responsible for the constricted outflow bear down too strongly, the hurricane undergoes acute shearing. As outlined above, this can be devastating.

After landfall. Tropical cyclones cannot survive over land, once their access to warm SST is removed. A powerful hurricane, such as Hugo, which hit Charleston, S.C. in 1989, can project life-threatening hurricane force winds over two hundred miles inland. As the storm progresses inland, it can dump a huge amount of rain—sometimes measured in feet. The storm may evolve into a frontal cyclone that continues to cause widespread damage. The best example of this is Hurricane Camille in 1969—the strongest hurricane ever to make landfall on the continental United States with winds sustained at 190 mph and gusts well exceeding 200 mph—which roared up the Mississippi Valley and eventually exited off the East Coast. Camille maintained tropical storm strength as far as Memphis, Tennessee. Most hurricanes will diminish in strength rapidly after landfall, reaching tropical depression strength by 48 to 72 hours. The main threat from the dying storm is from tornadoes and inland flooding. The right-hand quadrant of a hurricane or typhoon (in the Northern Hemisphere, left-hand in the Southern Hemisphere) is most frequently the strong side of the storm. This is because the forward motion is added to the counter-clockwise punch of the storm. Thus, the right-hand side of the hurricane contains the strong on-shore flow. This is where the maximum storm surge flooding, and the greatest potential loss of life, will be experienced. After landfall, the friction of the circulation moving over land causes a great deal of turbulence, which results in tornadoes. These are especially likely in the forward right-hand side of the storm’s path. The dying cyclone will dump many inches of rain. The lack of access to a warm sea surface results in the death of the tropical cyclone. It usually merges into a frontal trough, or dissipates.

Global Tropics Hazards and Benefits Outlook
Graphic provided by Climate Prediction Center