WDXS31 PGTW 270300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (GAMANE) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.9S 50.1E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 390 NM NORTH-NORTHEAST OF ANTANANARIVO,
MADAGASCAR
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 20S APPROACHING THE COAST OF NORTHWESTERN MADAGASCAR IN THE
VICINITY OF AMPISIKANANA WITHIN A COMPETING STEERING ENVIRONMENT 
BETWEEN NEAR EQUATORIAL RIDGES (NER) TO THE NORTH AND EAST AND A 
SUBTROPICAL RIDGE TO THE SOUTH. THE SYSTEM HAS CONTINUED TO RAPIDLY 
INTENSIFY OVER THE LAST SIX HOURS, REVEALING A RAGGED CLOUD-FILLED EYE
ON EIR. A 270013Z SSMIS 89GHZ MICROWAVE IMAGE DEPICTS A CRISP
MICROWAVE EYE STRUCTURE WITH WELL-DEFINED CLOUD BANDING WRAPPING
INTO THE VORTEX. AN ANTICYCLONE ALOFT PERSISTS AS THE SUBTROPICAL
JET TO THE SOUTH HAS CONTINUED TO ENHANCE STRONG POLEWARD OUTFLOW
AND FAVOR INTENSIFICATION. VERTICAL WIND SHEAR (VWS) REMAINS
MINIMAL AT 0-5KTS AND SEA SURFACE TEMPERATURES CONTINUE TO FUEL A
STRONG MOIST HEAT ENGINE. THE INITIAL POSITION WAS ASSESSED WITH
HIGH CONFIDENCE BASED ON THE MICROWAVE IMAGERY PREVIOUSLY MENTIONED
AND ANIMATED EIR DEPICTING A RAGGED EYE. THE INITIAL INTENSITY WAS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON EARLIER 261754Z ULTRA-HIGH
RESOLUTION METOP-B SCATTEROMETRY DATA CONVEYING ELEVATED WIND
SPEEDS OF 80-85KTS, AND THE AGENCY AND OBJECTIVE FIXES LISTED
BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   KNES: T5.0 - 90 KTS
   DEMS: T5.0 - 90 KTS
   FMEE: T5.0 - 90 KTS
   CIMSS SATCON: 70 KTS AT 270030Z
   CIMSS ADT: 74 KTS AT 270000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: TC 20S HAS CONTINUED TO RAPIDLY
INTENSIFY OVER THE LAST 12 HOURS, SO NEAR-TERM INTENSITIES ARE SET A 
BIT HIGHER THAN THE PREVIOUS FORECAST. 

FORECAST DISCUSSION: TC 20S IS FORECAST TO MAKE LANDFALL ON THE
COAST OF MADAGASCAR WITHIN THE NEXT 12 HOURS AS IT REMAINS IN A
COMPETING STEERING ENVIRONMENT. ONCE IT MAKES LANDFALL, THE SYSTEM IS
ANTICIPATED TO ROUND THE WESTERN EDGE OF A NER TO THE EAST, 
INTERACTING WITH THE MOUNTAINOUS TERRAIN OF NORTHERN MADAGASCAR BEFORE 
BEGINNING TO CURVE TO THE SOUTHEAST BETWEEN TAU 24 AND 36, CONTINUING 
TO RIDE THE WESTERN PERIPHERY OF THE EASTERN NER. THE SYSTEM IS
ANTICIPATED TO CONTINUE ON A SOUTHEASTERLY TRACK THROUGH THE END OF 
THE FORECAST PERIOD. PRIOR TO MAKING LANDFALL, THE SYSTEM IS EXPECTED 
TO REACH A PEAK INTENSITY ABOVE 90KTS BETWEEN TAU 0 AND TAU 12. ONCE 
TC 20S MAKES LANDFALL, MOIST INFLOW WILL BE RESTRICTED AND THE WESTERN 
PORTION OF THE SYSTEM WILL INTERACT WITH THE MOUNTAINOUS TOPOGRAPHY OF 
NORTHERN MADAGASCAR, INITIATING WEAKENING THROUGH THE FIRST 48 HOURS 
BEFORE THE SYSTEM COMES BACK OUT OVER WATER. VWS IS FORECAST TO 
INCREASE TO 20-25KTS BY THAT TIME, PREVENTING REINTENSIFICATION. THE 
SYSTEM WILL UNDERGO SUBTROPICAL TRANSITION AS IT INTERACTS WITH A 
CUTOFF LOW TO THE SOUTHWEST IN THE EXTENDED FORECAST PERIOD. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE HAS SOME
DISAGREEMENT IN THE NEAR-TERM WITH RESPECT TO HOW FAR TC 20S WILL
MOVE INTO MADAGASCAR AFTER LANDFALL. THE CROSS-TRACK ERROR AT TAU 24 
IS 100NM. ADDITIONALLY, THERE APPEARS TO BE DISAGREEMENT IN HOW 
QUICKLY THE SYSTEM WILL TRANSIT TO THE SOUTHEAST, LIKELY DUE TO 
DIFFERENCES IN MODEL INTERPRETATION HOW THE NER TO THE EAST WILL 
RECEDE TOWARDS THE CENTRAL INDIAN OCEAN. THE INTENSITY MODEL GUIDANCE 
IS IN AGREEMENT THAT THE SYSTEM WILL WEAKEN OVER THE COURSE OF THE 
FIRST 48 HOURS, BUT THERE IS SOME DISAGREEMENT REGARDING THE RATE OF 
WEAKENING THEREAFTER, ALTHOUGH MOST OF THE GUIDANCE KEEPS THE SYSTEM 
INTENSITY ABOVE 35KTS THROUGH THE FORECAST PERIOD. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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