WDIO31 PGTW 081500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 02B (ASANI) WARNING 
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.6N 87.8E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 601 NM SOUTH OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TC 02B IS STRUGGLING AGAINST THE INCREASING (25-30 KNOTS) EASTERLY
VERTICAL WIND SHEAR (VWS) AS INDICATED IN ANIMATED ENHANCED
INFRARED (EIR) SATELLITE IMAGERY, WHICH DEPICTS RAPIDLY DIMINISHING
CORE CONVECTION, INCLUDING THE LOSS OF THE CENTRAL DENSE OVERCAST.
HOWEVER, A 081217Z GMI 37GHZ MICROWAVE IMAGE REVEALS TIGHTLY-CURVED 
SHALLOW BANDING OVER THE EASTERN SEMICIRCLE WRAPPING INTO A WELL-
DEFINED LOW-LEVEL CIRCULATION CENTER WITH THE BULK OF THE DEEP 
CONVECTION DISPLACED OVER THE SOUTHWESTERN QUADRANT. THE INITIAL 
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE GMI IMAGE. 
BECAUSE THE CONVECTIVE STRUCTURE DETERIORATED SO QUICKLY, THE 
INITIAL INTENSITY IS HELD CONSERVATIVELY AT 65 KTS BASED ON THE PGTW 
DVORAK ESTIMATE AND THE CIMSS ADT ESTIMATE, HOWEVER, THERE IS MEDIUM 
CONFIDENCE. ADDITIONALLY, A FORTUITOUS 081212Z SMAP PASS SHOWS A 
SWATH OF 55-61 KNOT (ONE-MINUTE AVERAGE) WINDS, WHICH SUPPORTS A 60-
65 KNOT INTENSITY.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) ENTRENCHED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   CIMSS SATCON: 59 KTS AT 080756Z
   CIMSS ADT: 63 KTS AT 081215Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 25-30 KTS
   SST: 31-32 CELSIUS
   OUTFLOW: STRONG WESTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 02B IS EXPECTED TO CONTINUE TRACKING
NORTHWESTWARD ALONG THE PERIPHERY OF THE STR THROUGH TAU 36. ROBUST
WESTWARD OUTFLOW SHOULD ALLOW TC 02B TO MAINTAIN ITS CURRENT
INTENSITY THROUGH TAU 12 WITH STEADY WEAKENING THROUGH THE
REMAINDER OF THE FORECAST PERIOD DUE TO PERSISTENT VWS, DECREASING 
POLEWARD OUTFLOW AND EVENTUALLY DRY AIR ENTRAINMENT OFF THE DECCAN 
PLATEAU. AFTER TAU 36, INCREASING WESTERLIES OVER NORTHEAST INDIA 
WILL GRADUALLY ERODE THE STR ALLOWING THE SYSTEM TO TURN POLEWARD. 
AFTER TAU 72, TC 02B WILL TRACK NORTHEASTWARD AND WILL INTERACT WITH 
THE MIDLATITUDE TROUGH EXPECTED TO DEEPEN OVER THE NORTHERN BAY OF 
BENGAL WITH DISSIPATION ANTICIPATED NO LATER THAN TAU 120.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 36 BUT DIVERGES QUICKLY THROUGH THE REMAINDER OF THE
FORECAST PERIOD. ALTHOUGH NAVGEM REMAINS THE WESTERN MOST OUTLIER,
IT NOW INDICATES A SHARP RECURVE NORTH-NORTHEASTWARD ALONG THE
EASTERN COAST OF INDIA. THE BULK OF THE NUMERICAL GUIDANCE
INDICATES A TRACK TOWARD KOLKATA, INDIA AND BANGLADESH WITH AFUM
TRACKING THE SYSTEM INTO NORTHEAST INDIA AND GFS TRACKING THE
SYSTEM INTO MYANMAR. THE 080000Z ECMWF ENSEMBLE (EPS) STRIKE
PROBABILITY PRODUCT CONTINUES TO SHOW A HIGH PROBABILITY OF THE
SYSTEM TRACKING ALONG OR JUST EAST OF THE NORTHEAST COAST OF INDIA.
THERE ARE ALSO SIGNIFICANT DIFFERENCES IN ALONG TRACK SPEED AFTER
TAU 72 SO LOW CONFIDENCE IN THE JTWC TRACK FORECAST IN THE EXTENDED
PERIOD. OVERALL, THERE IS MEDIUM CONFIDENCE IN THE JTWC INTENSITY
FORECAST BUT INCREASING UNCERTAINTY IF TC 02B TRACKS CLOSER TO
LAND.

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