Subject: Indian-S: 1. Tropical Cyclone 20s (alistair) Warning Nr 011

From: SIU Weather Processor <[email-masked]>
Date: Thu, 19 Apr 2001 08:39:37 -0500

WTXS31 PGTW 191500
1. TROPICAL CYCLONE 20S (ALISTAIR) WARNING NR 011
   01 ACTIVE TROPICAL CYCLONE IN SOUTHERN HEMISPHERE
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
    ---
   WARNING POSITION:
   191200Z3 --- NEAR 17.5S3 120.3E6
     MOVEMENT PAST SIX HOURS - 225 DEGREES AT 10 KTS
     POSITION ACCURATE TO WITHIN 060 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 060 KT, GUSTS 075 KT
   RADIUS OF 050 KT WINDS - 035 NM SOUTHEAST SEMICIRCLE
                            025 NM ELSEWHERE
   RADIUS OF 035 KT WINDS - 075 NM SOUTHEAST SEMICIRCLE
                            055 NM ELSEWHERE
   REPEAT POSIT: 17.5S3 120.3E6
    ---
   FORECASTS:
   12 HRS, VALID AT:
   200000Z2 --- 18.5S4 118.6E6
   MAX SUSTAINED WINDS - 055 KT, GUSTS 070 KT
   DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
   RADIUS OF 050 KT WINDS - 035 NM SOUTHEAST SEMICIRCLE
                            025 NM ELSEWHERE
   RADIUS OF 035 KT WINDS - 075 NM SOUTHEAST SEMICIRCLE
                            055 NM ELSEWHERE
   VECTOR TO 24 HR POSIT: 235 DEG/ 10 KTS
    ---
   24 HRS, VALID AT:
   201200Z5 --- 19.6S6 116.8E6
   MAX SUSTAINED WINDS - 055 KT, GUSTS 070 KT
   DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
   RADIUS OF 050 KT WINDS - 030 NM SOUTHEAST SEMICIRCLE
                            025 NM ELSEWHERE
   RADIUS OF 035 KT WINDS - 070 NM SOUTHEAST SEMICIRCLE
                            050 NM ELSEWHERE
   VECTOR TO 36 HR POSIT: 235 DEG/ 08 KTS
    ---
   36 HRS, VALID AT:
   210000Z3 --- 20.6S8 115.4E1
   MAX SUSTAINED WINDS - 050 KT, GUSTS 065 KT
   DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
   RADIUS OF 050 KT WINDS - 025 NM SOUTHEAST SEMICIRCLE
                            015 NM ELSEWHERE
   RADIUS OF 035 KT WINDS - 065 NM SOUTHEAST SEMICIRCLE
                                   OVER WATER
                            045 NM ELSEWHERE
   VECTOR TO 48 HR POSIT: 225 DEG/ 08 KTS
    ---
   EXTENDED OUTLOOK:
   48 HRS, VALID AT:
   211200Z6 --- 21.7S0 114.2E8
   MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT
   DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
   RADIUS OF 035 KT WINDS - 060 NM SOUTHEAST SEMICIRCLE
                                   OVER WATER
                            040 NM ELSEWHERE
   VECTOR TO 72 HR POSIT: 190 DEG/ 07 KTS
    ---
   72 HRS, VALID AT:
   221200Z7 --- 24.5S1 113.6E1
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
    ---
REMARKS:
191500Z6 POSITION NEAR 17.8S6  119.9E0.
TROPICAL CYCLONE (TC) 20S (ALISTAIR), LOCATED APPROXIMATELY 115 NM
WEST-NORTHWEST OF BROOME, AUSTRALIA, HAS TRACKED SOUTHWESTWARD AT 10
KNOTS OVER THE PAST 6 HOURS. THE WARNING POSITION IS BASED ON
191130Z5 INFRARED SATELLITE IMAGERY. THE WARNING INTENSITY IS BASED
ON CURRENT INTENSITY ESTIMATES OF 55 AND 65 KNOTS. ENHANCED INFRARED
ANIMATION DEPICTS A POORLY DEFINED LOW-LEVEL CIRCULATION CENTER.
DIFFLUENCE ALOFT ASSOCIATED WITH THE WESTERN EXTENT OF THE
SUBTROPICAL RIDGE HAS HELPED TO GENERATE A NEW BURST OF DEEP
CONVECTION OVER THE WESTERN QUADRANT. TC 20S IS FORECAST TO TRACK
SOUTHWESTWARD UNDER THE STEERING INFLUENCE OF THE MID-LEVEL RIDGE
ESTABLISHED OVER WESTERN AUSTRALIA THROUGH 48 HOURS. AFTERWARD, THE
SYSTEM SHOULD BEGIN TO TRACK MORE SOUTHWARD WITH AN APPROACH OF A
MID-LATITUDE FROM THE SOUTHWEST. TC 20S HAS BEGUN ITS TRACK POLEWARD
OF THE SUBTROPICAL RIDGE AXIS AND INTO A REGION OF LIGHT TO MODERATE
UPPER WEST-NORTHWESTERLIES. THEREFORE, THE SYSTEM SHOULD SHOW A
WEAKENING TREND THROUGH THE PERIOD. MAXIMUM SIGNIFICANT WAVE HEIGHT
AT 191200Z3 IS 14 FEET. NEXT WARNINGS AT 192100Z3 ,200300Z5, 200900Z1
AND 201500Z8.//

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