WDIO31 PGTW 300900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (FENGAL) WARNING 
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.4N 80.9E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 747 NM SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 04B (FENGAL) WITH PERSISTENT DEEP CONVECTION PARTIALLY
OBSCURING THE LOW-LEVEL CIRCULATION CENTER. THE SYSTEM IS CURRENTLY
ANALYZED TO BE ABOUT 45 NM OFF THE COAST OF INDIA WITH THE CENTER
SLIGHTLY OFFSET TO THE EAST OF THE DEEP CONVECTION DUE TO ELEVATED
EASTERLY VERTICAL WIND SHEAR. ENVIRONMENTAL ANALYSIS INDICATES THAT
04B IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY
STRONG POLEWARD OUTFLOW ALOFT, MODERATE TO HIGH (20-25 KTS)
VERTICAL WIND SHEAR, AND WARM (27-28 C) SEA SURFACE TEMPERATURES.
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON
ANIMATED RADAR IMAGERY AND EXTRAPOLATION FROM A 300420Z ASCAT-B
IMAGE. THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE MENTIONED ASCAT-B IMAGE SHOWING 40 KNOT
WINDS WITHIN THE SOUTHERN AND WESTERN PERIPHERIES ALONG WITH THE
AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF AN EXTENSION OF A
SUBTROPICAL RIDGE (STR) TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS ADT: 55 KTS AT 300600Z
   CIMSS AIDT:44 KTS AT 300600Z
   CIMSS DPRINT: 48 KTS AT 300530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 04B IS FORECAST TO CONTINUE TRACKING WESTWARD
ALONG THE SOUTHERN PERIPHERY OF AN EXTENSION OF THE STR TO THE
EAST, TOWARD THE COAST OF INDIA, WITH LANDFALL EXPECTED TO OCCUR
BETWEEN TAU 12 AND 24. THE SYSTEM IS FORECAST TO GRADUALLY WEAKEN
AS IT MAKES LANDFALL WITH AN INTENSITY OF AROUND 40 KTS DUE TO HIGH
VERTICAL WIND SHEAR VERTICAL WIND SHEAR AND INCREASING TERRAIN
INTERACTION. AFTER MAKING LANDFALL, 04B WILL CONTINUE TO DEGRADE AS
IT MOVES FURTHER INLAND WITH A DROP IN INTENSITY TO BELOW TROPICAL
STORM STRENGTH NEAR TAU 36. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS OVERALL IN GOOD
AGREEMENT ON A SLOW WESTWARD TRACK WITH THE EXCEPTION OF GFS AND
ITS ENSEMBLE MEAN (GEFS). GFS AND GEFS BOTH SUGGEST A STALL OFF THE
COAST OVER THE NEXT 48 HOURS BEFORE TURNING WESTWARD AND ARE THE
MAIN OUTLIERS WITHIN THE TRACK GUIDANCE. ALL OTHER MODELS SUGGEST
THE WESTWARD TRACK, AND THE JTWC TRACK FORECAST IS PLACED WITHIN
THE MAIN ENVELOPE OF GUIDANCE WITH MEDIUM CONFIDENCE. INTENSITY
GUIDANCE PAINTS A SIMILAR PICTURE WITH GFS KEEPING THE VORTEX
STRONGER FOR LONGER (DUE TO LESS TERRAIN INTERACTION). THE
REMAINDER OF INTENSITY GUIDANCE HAS A STEEPER WEAKENING TREND, AND
THE JTWC INTENSITY FORECAST ALSO FOLLOWS THE MAIN GROUPING WITH
MEDIUM CONFIDENCE. THE STALL OFF THE COAST SHOULD NOT BE COMPLETELY
DISCOUNTED THOUGH AS THE OVERALL STEERING PATTERN IS RELATIVELY
WEAK. IF THE EXTENSION OF THE RIDGE LOSES INFLUENCE ON THE VORTEX,
IT COULD STALL BEFORE THE RIDGING BUILDS BACK UP AND
PUSHES THE SYSTEM INLAND.

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