WDXS31 PGTW 180300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (EMNATI) WARNING 
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.4S 63.0E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 518 NM NORTHEAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CONSOLIDATING SYSTEM ATTEMPTING TO FORM AN SUSTAINED EYE WITHIN
CENTRAL, FLARING CONVECTION. A 1747Z ASCAT-B IMAGE DEPICTS A
WELL-DEFINED CIRCULATION 45-50 KT WINDS AT THE CENTER OF THE
WIND FIELD. A 172137Z AMSR2 37GHZ IMAGE DEPICTS A MICROWAVE EYE FROM
WHICH THE INITIAL POSITION IS EXTRAPOLATED AND LENDS SUPPORT TO THE
PGTW FIX POSITION. THE INITIAL INTENSITY IS BASED ON AN AVERAGE OF
THE AGENCY DVORAK CURRENT INTENSITY ESTIMATES AND ADT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   FMEE: T3.5 - 55 KTS
   CIMSS SATCON: 63 KTS AT 172038Z
   CIMSS ADT: 59 KTS AT 172115Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 13S WILL BEGIN TURNING WEST-SOUTHWESTWARD
WITHIN THE NEXT 12 HOURS AS IT TRACKS TOWARD A BREAK IN THE
SUBTROPICAL RIDGE DUE TO AN APPROACHING MID-LATITUDE TROUGH FROM
THE SOUTHWEST. THE SYSTEM WILL CONTINUE THIS GENERAL DIRECTION AND
REACH A PEAK INTENSITY OF 95 KTS AROUND TAU 72. AFTERWARDS, LOW
OCEAN HEAT CONTENT NEAR MADAGASCAR CAUSED BY UPWELLING DUE TO THE 
PASSAGE OF ANOTHER TROPICAL CYCLONE A FEW DAYS EARLIER, WILL LEAD TO 
A DECREASE IN INTENSITY, REACHING 80 KTS BY TAU 96. BY TAU 120, THE 
CENTER OF THE SYSTEM WILL BE OVER CENTRAL MADAGASCAR, FURTHER 
DECREASING THE SYSTEM TO 65 KTS. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT WITH ONLY
A 100NM CROSS-TRACK SPREAD AT TAU 96 EXCLUDING NVGM AS AN OUTLIER
TO THE SOUTH. TC 13S WAS EXPECTED TO HAVE ALREADY TURNED
SOUTH-SOUTHWEST, SO THE JTWC FORECAST TRACK IS PLACED JUST SLIGHTLY
NORTH OF CONSENSUS TO OFFSET THIS. INTENSITY GUIDANCE IS ALSO IN
GOOD AGREEMENT WITH HWRF AND GFS BOTH PEAKING INTENSITY AT 95 KTS
AT TAU 72. 

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