WDIO31 PGTW 292100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (FENGAL) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.4N 81.8E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 98 NM EAST-SOUTHEAST OF CHENNAI, INDIA
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
OBSCURED LOW LEVEL CIRCULATION CENTER (LLCC), DISPLACED TO THE
SOUTHEAST OF A BURGEONING CONVECTIVE BURST. THERE HAS NOT BEEN A
GOOD MICROWAVE PASS SINCE A 291231Z WSF-M PASS, WHICH INDICATED
THAT THE LLCC IS IN FACT DISPLACED SOUTHEAST COMPARED TO THE
UPPER-LEVEL ROTATION. ANIMATED RADAR DATA FROM INDIA SHOWS THE
WESTERN PORTION OF THE CIRCULATION BUT IS NOT CURRENTLY ABLE TO SEE
THE ENTIRETY OF THE LLCC THOUGH PROVIDES ENOUGH OF A VIEW TO SUPPORT
THE FACT THAT THE CENTER IS SOMEWHERE ALONG THE EASTERN EDGE OF THE
DEVELOPING CDO FEATURE. THUS, THE INITIAL POSITION IS ASSESSED WITH
MEDIUM CONFIDENCE. REANALYSIS OF EARLIER POSITIONS INDICATES THE
SYSTEM REACHED TROPICAL STORM STRENGTH AS EARLY AS 280600Z AND
LIKELY PEAKED AROUND 281200Z. THE INITIAL INTENSITY IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE HIGHER END OF AVAILABLE
OBJECTIVE INTENSITY ESTIMATES, WHICH RANGE BETWEEN T2.5 TO T3.0,
COMBINED WITH AN EARLY CIMSS DPRINT ESTIMATE OF 48 KNOTS. EARLIER
SCATTEROMETER DATA SHOWED WINDS UP TO 40 KNOTS ACROSS THE NORTHERN
ARC OF THE SYSTEM, WHILE WINDS TO THE SOUTH REMAIN MUCH LIGHTER.
THE ENVIRONMENT IS MARGINALLY FAVORABLE, WITH GOOD POLEWARD OUTFLOW
AND WARM SSTS. HOWEVER, WHILE THERE STILL ARE NO CIMSS SHEAR
ESTIMATES, MODEL SKEW-T DATA AND THE GENERAL APPEARANCE ARE HIGHLY
SUGGESTIVE OF A MODERATE AMOUNT OF SOUTHEASTERLY SHEAR IMPACTING
THE SYSTEM.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: THE STEERING PATTERN IS GENERALLY WEAK,
BUT IN THE AGGREGATE THE SYSTEM IS TRACKING ALONG THE WESTERN
PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED TO THE
EAST.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   DEMS: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 04B (FENGAL) FORMED
OVERNIGHT BASED ON REANALYSIS OF EARLIER POSITIONS, TO THE EAST OF
CHENNAI, INDIA. THE SYSTEM IS EXPECTED TO TRACK TOWARDS THE COAST
OVER THE NEXT 36 HOURS, IN AN OVERALL WEAK STEERING ENVIRONMENT.
THE WEAKNESS IN THE STEERING PATTERN MEANS THAT THE SYSTEM WILL
MOVE VERY SLOWLY AND COULD ACTUALLY STALL OUT VERY NEAR THE
COASTLINE, AS DEPICTED IN THE LATEST GFS MODEL. THE REMAINDER OF
THE MODELS HOWEVER SUPPORT A SLOW NORTHWESTWARD TO WESTWARD TRACK,
WITH THE SYSTEM MAKING LANDFALL NEAR CHENNAI IN ABOUT 36 HOURS. IN
TERMS OF INTENSITY, THE SYSTEM HAS LIKELY ALREADY PEAKED IN
INTENSITY AND UPPER-LEVEL CONDITIONS ARE EXPECTED TO BECOME LESS
FAVORABLE OVER THE NEXT 12 TO 36 HOURS. THE ONGOING BURST OF DEEP
CONVECTION IS IMPRESSIVE, BUT IT IS UNLIKELY THAT IT WILL PERSIST
FOR LONG DUE TO THE MODERATE AND INCREASING SOUTHEASTERLY SHEAR. SO
THE SYSTEM WILL MAINTAIN A STEADY INTENSITY FOR THE NEXT 12 HOURS
BEFORE BEGINNING TO SLOWLY WEAKEN AS IT APPROACHES LANDFALL. AFTER
LANDFALL, THE SYSTEM WILL QUICKLY DISSIPATE AS IT SLOWLY CONTINUES
INLAND TO THE WEST OF CHENNAI. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GENERALLY GOOD
AGREEMENT ON THE OVERALL TRACK FORECAST, WITH THE BULK OF THE
MODELS SHOWING A SLOWLY ARCING TRACK WITH LANDFALL IN ABOUT 36
HOURS. THE GFS AND GEFS ENSEMBLE, HOWEVER, ARE THE NOTABLE OUTLIERS,
AND BOTH KEEP THE SYSTEM OFFSHORE, IN FACT MOVING IT BACK EASTWARD
AFTER MAKING A HEAD FAKE TOWARDS CHENNAI THEN CIRCLING BACK FOR A
LANDFALL IN ABOUT 84 HOURS. THE JTWC FORECAST IS CONSISTENT WITH
THE BULK OF THE GUIDANCE AND IS CLOSE TO THE CONSENSUS MEAN.
LIMITED INTENSITY GUIDANCE SHOWS THE SYSTEM MAINTAINING INTENSITY
FOR THE FIRST 12 HOURS THEN SLOWLY WEAKENING TO DISSIPATION. 

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