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Tropical Cyclone ALDA : JTWC Advisories
Season 1998-1999 Summaries (Operational Data): [AU] [SIO] [SPAC] [SH]
---> Tropical Cyclone ALDA Track Map and Data

WTXS21 PGTW 990116 11:00z
161051Z JAN 99//
RMKS/
1. IMMEDIATE DELIVERY REQ TO AMEMBASSY PORT LOUIS
2. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
170 NM EITHER SIDE OF A LINE FROM 20.7S9 39.7E9 TO 24.6S2 43.3E0
WITHIN THE NEXT 03 TO 24 HOURS.  AVAILABLE DATA DOES NOT JUSTIFY
ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME.
WINDS IN THE AREA ARE ESTIMATED TO BE 20 TO 25 KNOTS. METSAT
IMAGERY AT 160830Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 21.2S5 40.2E6.  THE SYSTEM IS MOVING EAST-SOUTHEASTWARD AT
05 KNOTS.
3. REMARKS: ANIMATED VISIBLE AND INFRARED SATELLITE IMAGERY INDICATE
THE AREA OF CONVECTION IN THE MOZAMBIQUE CHANNEL HAS SHOWN
INCREASING ORGANIZATION OVER THE LAST 6 HOURS. A WEAK LOW LEVEL
CICULATION CENTER IS ALSO PRESENT AND MOVING TO THE SOUTHEAST. THIS
SYSTEM IS MOVING INTO A HIGH VERTICAL WIND SHEAR ENVIRONMENT WHICH
MAY RETARD DEVELOPMENT. HOWEVER, THE POTENTIAL FOR THE DEVELOPMENT
OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS GOOD.
4. THIS ALERT VALID UNTIL 171100Z0.
=========================================================================
WTXS31 PGTW 990116 21:00z
IMMEDIATE DELIVERY REQ TO AMEMBASSY PORT LOUIS
1. TROPICAL CYCLONE 12S (ALDA) WARNING NR 001    
   02 ACTIVE TROPICAL CYCLONES IN SOUTHERN HEMISPHERE
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
    ---
   WARNING POSITION:
   161800Z6 --- NEAR 22.7S1 40.8E2
     MOVEMENT PAST SIX HOURS - 160 DEGREES AT 08 KTS
     POSITION ACCURATE TO WITHIN 060 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   REPEAT POSIT: 22.7S1 40.8E2
    ---
   FORECASTS:
   12 HRS, VALID AT:
   170600Z4 --- 24.7S3 41.1E6
   MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
   RADIUS OF 035 KT WINDS - 155 NM EAST SEMICIRCLE       
                            110 NM ELSEWHERE
   VECTOR TO 24 HR POSIT: 165 DEG/ 12 KTS
    ---
   24 HRS, VALID AT:
   171800Z7 --- 27.1S0 41.8E3
   MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT
   BECOMING EXTRATROPICAL
   RADIUS OF 035 KT WINDS - 175 NM NORTHEAST SEMICIRCLE  
                            110 NM ELSEWHERE
   VECTOR TO 36 HR POSIT: 145 DEG/ 16 KTS
    ---
   36 HRS, VALID AT:
   180600Z5 --- 29.7S8 44.0E8
   MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
   BECOMING EXTRATROPICAL
   RADIUS OF 035 KT WINDS - 175 NM NORTHEAST SEMICIRCLE  
                            110 NM ELSEWHERE
   VECTOR TO 48 HR POSIT: 125 DEG/ 20 KTS
    ---
   EXTENDED OUTLOOK:
   48 HRS, VALID AT:
   181800Z8 --- 31.9S3 48.0E2
   MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
   EXTRATROPICAL
    ---
REMARKS:
162100Z0 POSITION NEAR 23.2S7 40.9E3.
TROPICAL CYCLONE 12S (ALDA) IS MOVING SOUTH-SOUTHEASTWARD AT 08 
KNOTS. THE WARNING POSITION AND INTENSITY ARE BASED ON A 161731Z9 
INFRARED SATELLITE INTENSITY ESTIMATE OF T2.0 (30 KNOTS). 160701Z5 
SCATTEROMETER DATA INDICATES 30 TO 35 KNOT SURFACE WINDS CONVERGING 
ON THE EASTERN SIDE OF THIS SYSTEM. ANIMATED INFRARED SATELLITE 
IMAGERY INDICATES THIS SYSTEM APPEARS TO BE DEVELOPING SUBTROPICAL 
CHARACTERISTICS. TC 12S (ALDA) IS FORECAST TO ACCELERATE 
SOUTHEASTWARD THROUGHOUT THE FORECAST PERIOD AND COMPLETE TRANSITION 
INTO AN EXTRATROPICAL SYSTEM BY 48 HOURS. THE INTENSITY IS EXPECTED 
TO INCREASE SLIGHTLY DUE TO INCREASED TRANSLATIONAL SPEED, THEN 
WEAKEN AS THE SYSTEM BECOMES EXTRATROPICAL. WIND RADII ARE 
EXTRAPOLATED FROM 160701Z5 SCATTEROMETER DATA. MAXIMUM SIGNIFICANT 
WAVE HEIGHT AT 161800Z6 IS 16 FEET. THIS WARNING SUPERSEDES AND 
CANCELS NAVPACMETOCCEN 161051Z JAN 99 TROPICAL CYCLONE FORMATION 
ALERT (WTXS21 PGTW 161100) FUTURE WARNINGS WILL COMMENCE AT 170300Z1 
(DTG 170153Z7) AND 171500Z4 (DTG 171353Z0). REFER TO TROPICAL 
CYCLONE 11P (DANI) WARNINGS (WTPS31 PGTW) FOR TWELVE-HOURLY 
UPDATES.//
=========================================================================
WTXS31 PGTW 990117 03:00z    
IMMEDIATE DELIVERY REQ TO AMEMBASSY PORT LOUIS
1. TROPICAL CYCLONE 12S (ALDA) WARNING NR 002    
   02 ACTIVE TROPICAL CYCLONES IN SOUTHERN HEMISPHERE
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
    ---
   WARNING POSITION:
   170000Z8 --- NEAR 23.3S8 40.5E9
     MOVEMENT PAST SIX HOURS - 180 DEGREES AT 06 KTS
     POSITION ACCURATE TO WITHIN 060 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   REPEAT POSIT: 23.3S8 40.5E9
    ---
   FORECASTS:
   12 HRS, VALID AT:
   171200Z1 --- 24.7S3 40.6E0
   MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
   BECOMING EXTRATROPICAL
   RADIUS OF 035 KT WINDS - 135 NM EAST SEMICIRCLE       
                            085 NM ELSEWHERE
   VECTOR TO 24 HR POSIT: 170 DEG/ 10 KTS
    ---
   24 HRS, VALID AT:
   180000Z9 --- 26.6S4 41.0E5
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   BECOMING EXTRATROPICAL
   VECTOR TO 36 HR POSIT: 155 DEG/ 17 KTS
    ---
   36 HRS, VALID AT:
   181200Z2 --- 29.6S7 42.8E4
   MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
   EXTRATROPICAL
    ---
REMARKS:
170300Z1 POSITION NEAR 23.7S2 40.5E9. 
TROPICAL CYCLONE 12S (ALDA) IS MOVING SOUTHWARD AT 06 KNOTS. THE 
WARNING POSITION AND INTENSITY ARE BASED ON A 162331Z6 INFRARED 
SATELLITE INTENSITY ESTIMATE OF T2.5 (35 KNOTS). THIS SYSTEM IS 
EXPERIENCING MODERATE VERTICAL WIND SHEAR WHICH HAS DISSIPATED DEEP 
CONVECTION OVER AND NORTH OF THE LOW-LEVEL CIRCULATION CENTER. 
ANIMATED INFRARED SATELLITE IMAGERY INDICATES THIS SYSTEM CONTINUES 
TO TRANSITION INTO A SUBTROPICAL SYSTEM. TC 12S (ALDA) IS FORECAST 
TO ACCELERATE SOUTH-SOUTHEASTWARD THROUGHOUT THE FORECAST PERIOD AND 
COMPLETE TRANSITION INTO AN EXTRATROPICAL SYSTEM BY 36 HOURS. THE 
INTENSITY IS EXPECTED TO INCREASE SLIGHTLY DUE TO INCREASED 
TRANSLATIONAL SPEED, THEN WEAKEN AS THE SYSTEM BECOMES 
EXTRATROPICAL. THE MAJORITY OF DYNAMIC AND STATISTICAL OBJECTIVE 
GUIDANCE SUPPORTS THIS FORECAST SCENARIO. MAXIMUM SIGNIFICANT WAVE 
HEIGHT AT 170000Z8 IS 17 FEET. NEXT WARNINGS AT 171500Z4 (DTG 
171353Z0) AND 180300Z2 (DTG 180153Z8). REFER TO TROPICAL CYCLONE 11P 
(DANI) WARNINGS (WTXS31 PGTW) FOR TWELVE-HOURLY UPDATES.//
=========================================================================
WTXS31 PGTW 990117 15:00z
IMMEDIATE DELIVERY REQ TO AMEMBASSY PORT LOUIS
1. TROPICAL CYCLONE 12S (ALDA) WARNING NR 003
   02 ACTIVE TROPICAL CYCLONES IN SOUTHERN HEMISPHERE
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
    ---
   WARNING POSITION:
   171200Z1 --- NEAR 24.3S9 38.6E7
     MOVEMENT PAST SIX HOURS - 220 DEGREES AT 09 KTS
     POSITION ACCURATE TO WITHIN 060 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
   RADIUS OF 035 KT WINDS - 135 NM EAST SEMICIRCLE
                            085 NM ELSEWHERE
   REPEAT POSIT: NEAR 24.3S9 38.6E7
    ---
   FORECASTS:
   12 HRS, VALID AT:
   180000Z9 --- 25.7S4 37.7E7
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   BECOMING EXTRATROPICAL
   VECTOR TO 24 HR POSIT: 165 DEG/ 11 KTS
    ---
   24 HRS, VALID AT:
   181200Z2 --- 27.9S8 38.3E4
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   EXTRATROPICAL
    ---
REMARKS:
171500Z4 POSITION NEAR 24.7S3 38.4E5.
TROPICAL CYCLONE 12S (ALDA) IS MOVING SOUTHWESTWARD AT 06 KNOTS WEST
OF MADAGASCAR. THE WARNING POSITION IS BASED UPON ANIMATED VISIBLE
SATELLITE IMAGERY, AND THE WARNING INTENSITY IS BASED UPON A
COMBINATION OF A 171131Z4 VISIBLE SATELLITE IMAGE WITH A CURRENT
INTENSITY ESTIMATE OF 25 KNOTS AND SHIP SYNOPTIC DATA OF 40 KNOTS.
TROPICAL CYCLONE 12S (ALDA) WILL CONTINUE TO TRACK SOUTHWESTWARD
UNDER THE STEERING INFLUENCE OF A MID-LEVEL RIDGE TO ITS SOUTH AND
EAST. AS THE RIDGE WEAKENS IN 12 HOURS, ALDA WILL MOVE POLEWARD OVER
THE RIDGE AND BECOME EXTRATROPICAL. AS IT MOVES OVER THE RIDGE, IT
WILL ACCELERATE INTO THE SOUTHERN INDIAN OCEAN. THE INTENSITY IS
EXPECTED TO WEAKEN AS THE SYSTEM BECOMES EXTRATROPICAL. THE MAJORITY
OF DYNAMIC AND STATISTICAL OBJECTIVE GUIDANCE SUPPORTS THIS FORECAST
SCENARIO. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 171200Z1 IS 15 FEET.
THIS IS THE FINAL WARNING ON THIS SYSTEM BY THE JOINT TYPHOON
WARNING CENTER (NAVPACMETOCCEN PEARL HARBOR HI). THE SYSTEM WILL BE
CLOSELY MONITORED FOR SIGNS OF REGENERATION. REFER TO TROPICAL
CYCLONE 11P (DANI) WARNINGS (WTPS31 PGTW) FOR TWELVE-HOURLY
UPDATES.//
=========================================================================
WTXS31 PGTW 990118 15:00z
IMMEDIATE DELIVERY REQ TO AMEMBASSY PORT LOUIS
1. TROPICAL CYCLONE 12S (ALDA) WARNING NR 004
   02 ACTIVE TROPICAL CYCLONES IN SOUTHEB#35)###-M;GKUKS)M;W4JS-U#; O
NE-MINUTE AVERAGE
    ---
   WARNING POSITION:
   181200Z2 --- NEAR 28.0S0 39.2E4
     MOVEMENT PAST SIX HOURS - 170 DEGREES AT 09 KTS
     POSITION ACCURATE TO WITHIN 090 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 055 KT, GUSTS 070 KT
   RADIUS OF 050 KT WINDS - 025 NM
   RADIUS OF 035 KT WINDS - 110 NM EAST SEMICIRCLE
                            085 NM ELSEWHERE
   REPEAT POSIT: NEAR 28.0S0 39.2E4
    ---
   FORECASTS:
   12 HRS, VALID AT:
   190000Z0 --- 29.6S7 39.7E9
   MAX SUSTAINED WINDS - 050 KT, GUSTS 065 KT
   BECOMING EXTRATROPICAL
   RADIUS OF 035 KT WINDS - 120 NM NORTHEAST SEMICIRCLE
                            075 NM ELSEWHERE
   VECTOR TO 24 HR POSIT: 145 DEG/ 10 KTS
    ---
   24 HRS, VALID AT:
   191200Z3 --- 31.3S7 41.0E5
   MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT
   BECOMING EXTRATROPICAL
   RADIUS OF 035 KT WINDS - 120 NM NORTHEAST SEMICIRCLE
                            070 NM ELSEWHERE
   VECTOR TO 36 HR POSIT: 125 DEG/ 14 KTS
    ---
   36 HRS, VALID AT:
   200000Z2 --- 32.9S4 43.6E3
   MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT
   EXTRATROPICAL
    ---
REMARKS:
181500Z5 POSITION NEAR 28.4S4 39.3E5.
TROPICAL CYCLONE 12S (ALDA) HAS TRACKED SOUTHWARD AT 9 KNOTS OVER
THE PAST 6 HOURS WEST-SOUTHWEST OF MADAGASCAR. THE WARNING POSITION
IS BASED UPON 181100Z1 ANIMATED VISIBLE SATELLITE IMAGERY AND IS
CONSISTENT WITH EARLIER MICROWAVE IMAGERY FIXES. THE WARNING
INTENSITY IS BASED UPON AN 181100Z1 VISIBLE SATELLITE CURRENT
INTENSITY ESTIMATE OF 55 KNOTS. TROPICAL CYCLONE 12S (ALDA) IS
CURRENTLY UNDER THE STEERING INFLUENCE OF A RIDGE TO ITS EAST AND
SOUTH. WITHIN THE NEXT 12 TO 24 HOURS, THE RIDGE IS FORECAST TO
BECOME NORTHWEST TO SOUTHEAST ORIENTED, AND TC 12S (ALDA) WILL BEGIN
TO TRACK SOUTHEASTWARD. AS TC 12S (ALDA) MOVES POLEWARD OF THE
RIDGE, IT WILL ACCELERATE INTO THE SOUTHERN INDIAN OCEAN AND BEGIN
ITS EXTRATROPICAL TRANSITION. TROPICAL CYCLONE 12S (ALDA) SHOULD
WEAKEN SLIGHTLY IN INTENSITY AS THE SYSTEM MOVES INTO COLDER WATERS
AND BEGINS EXTRATROPICAL TRANSITION. ALTHOUGH TROPICAL CYCLONE 12S
(ALDA) APPEARS TO HAVE BOTH TROPICAL AND SUBTROPICAL HARACTERISTICS,
IT HAS YET TO UNDERGO  EXTRATROPICAL TRANSITION. SINCE TC 12S (ALDA)
HAS INDEED INTENSIFIED OVER THE PAST 24 HOURS BEFORE UNDERGOING
TRANSITION, JTWC HAS REGENERATED THE WARNINGS UNTIL TC 12S (ALDA)
UNDERGOES FULL EXTRATROPICAL TRANSITION. MAXIMUM SIGNIFICANT WAVE
HEIGHT AT 181200Z2 IS 20 FEET. NEXT WARNINGS AT 190300Z3 (DTG
190153Z9) AND 191500Z6 (DTG 191353Z2). REFER TO TROPICAL CYCLONE 11P
(DANI) WARNINGS (WTPS31 PGTW) FOR TWELVE-HOURLY UPDATES.//
=========================================================================
WTXS32 PGTW 990119 03:00z    
IMMEDIATE DELIVERY REQ TO AMEMBASSY PORT LOUIS
1. TROPICAL CYCLONE 12S (ALDA) WARNING NR 005    
   02 ACTIVE TROPICAL CYCLONES IN SOUTHERN HEMISPHERE
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
    ---
   WARNING POSITION:
   190000Z0 --- NEAR 30.8S1 43.6E3
     MOVEMENT PAST SIX HOURS - 120 DEGREES AT 25 KTS
     POSITION ACCURATE TO WITHIN 060 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT
   BECOMING EXTRATROPICAL
   RADIUS OF 035 KT WINDS - 075 NM NORTHEAST SEMICIRCLE  
                            055 NM ELSEWHERE
   REPEAT POSIT: 30.8S1 43.6E3
    ---
   FORECASTS:
   12 HRS, VALID AT:
   191200Z3 --- 33.4S0 48.5E7
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   BECOMING EXTRATROPICAL
   RADIUS OF 035 KT WINDS - 060 NM NORTHEAST SEMICIRCLE  
                            050 NM ELSEWHERE
   VECTOR TO 24 HR POSIT: 120 DEG/ 25 KTS
    ---
   24 HRS, VALID AT:
   200000Z2 --- 35.9S7 53.7E5
   MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
   EXTRATROPICAL
    ---
REMARKS:
190300Z3 POSITION NEAR 31.5S9   44.8E6.
TROPICAL CYCLONE 12S (ALDA) HAS TRACKED TOWARDS THE EAST-SOUTHEAST
AT 20 KNOTS DURING THE PAST 6 HOURS. THE WARNING POSITION AND 
INTENSITY IS BASED ON 182330Z7 SATELLITE IMAGERY (KGWC). TC 12S 
(ALDA) HAS A CURRENT INTENSITY OF T3.0 (45 KNOTS) BUT IS 
TRANSITIONING TO EXTRATROPICAL AS IT MOVES INTO HIGHER LATITUDES AND 
COOLER WATERS. TC 12S (ALDA) IS BEING STEERED BY BOTH THE 
SUBTROPICAL RIDGE TO ITS NORTHEAST AND AN APPROACHING LONGWAVE 
TROUGH TO ITS WEST. THE SYSTEM IS FORECAST TO CONTINUE TO TRACK 
TOWARDS THE EAST-SOUTHEAST OVER THE ENTIRE FORECAST PERIOD UNTIL 
BECOMING FULLY EXTRATROPICAL BY THE 24 HOUR PERIOD. TC 12S (ALDA) IS 
FORECAST TO SLOWLY DECREASE INTENSITY DURING THE FORECAST PERIOD, 
BUT MAY RETAIN SOME STRONGER WINDS ENHANCED BY THE LOCAL PRESSURE 
GRADIENT. MAXIMUM SIGNIFICANT WAVE HEIGHT AT190000Z IS 18 FEET. 
REFER TO WWPN30 PGFW FOR ADDITIONAL SEA HEIGHT INFORMATION. THIS IS 
THE FINAL WARNING ON THIS SYSTEM BY THE JOINT TYPHOON WARNING CENTER 
(NAVPACMETOCCEN WEST GU).  THE SYSTEM WILL BE CLOSELY MONITORED FOR 
SIGNS OF REGENERATION. REFER TO TROPICAL CYCLONE 11P (DANI) WARNINGS 
(WTXS31 PGTW) FOR TWELVE-HOURLY UPDATES.//

Tropical cyclone tracks developed by Michael Bath using operational warnings and advisories.


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Document: tropical_cyclone_alda_jtwc_advisories.htm Updated: 4 September 2016