WDIO31 PGTW 100300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 02B (ASANI) WARNING NR 
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.8N 83.9E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 533 NM SOUTH-SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE 02B (ASANI) HAS PEAKED AND IS SLOWING ITS SPEED OF
ADVANCE AS IT CHUGS TOWARDS THE INDIAN SUBCONTINENT.  ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWED A SURGE IN
CONVECTION ASSOCIATED WITH ITS DIURNAL MAXIMUM BUT RECENTLY IS 
SHOWING WARMING CLOUD TOPS AND WANING CONVECTION AS THE SUN CLIMBS 
OVER THE BAY OF BENGAL.  ANIMATED WATER VAPOR IMAGERY SHOWS A 
DISTINCT EDGE TO THE CONVECTIVE SHIELD OVER THE EASTERN HEMISPHERE OF 
THE STORM ASSOCIATED WITH MODERATE EASTERLY SHEAR ALOFT. EQUATORIAL 
OUTFLOW REMAINS VIGOROUS. TWO MICROWAVE SERIES CAME IN RECENTLY--A 
092315Z SMMIS AND A 100040Z GMI--VERIFYING SOLID POSITIONING ON THE 
FIX BUT ALSO SHOWING THAT THE STORM LACKS VIGOROUS CONVECTIVE BANDING 
IN ALL QUADRANTS. NONETHELESS, ASANI MANAGED TO BREAK TYPHOON 
STRENGTH JUST BEFORE FIX TIME. THE JTWC DVORAK ASSESSMENT SATCON AND 
ADT RAW VALUES ALL CONVERGED NEAR T4.0 AT ANALYSIS TIME. A BROAD WARM 
RIDGE EXTENDING NORTHWESTWARD FROM THE MALAY PENINSULA ALONG THE EAST
COAST OF TAILAND AND MYANMAR IS NUDGING THE SYSTEM WESTWARD BUT THE
INFLUENCE OF THE RIDGE IS WANING AND THE STORM IS EXHIBITING THE
FIRST HINTS OF ROLLING OVER TO A MORE POLEWARD TRACK. MODERATELY
FAVORABLE ATMOSPHERIC CONDITIONS AND WARM SEAS EXIST OVER THE
NORTHERN BAY OF BENGAL (BOB).  THE BASIN BEARS THE SIGNATURE OF A
PULSE FROM THE MADDEN JULIAN OSCILLATION INCLUDING A TWIN CYCLONE
IN THE SOUTHERN HEMISPHERE (TC 25S) BUT NCEP INSISTS THE
ENVIRONMENT IS A RESULT OF CONSTRUCTIVE INTERFERENCE BETWEEN ROSSBY
AND KELVIN WAVES. NONETHELESS THE EFFECTS ARE THE SAME AND 200MB
CHI ANOMALIES REVEAL A SPECTACULAR CHIMNEY OVER THE EQUATORIAL
REGION FROM THE CENTRAL BAY OF BENGAL THROUGH THE MARITIME
CONTINENT. THE FURTHER TC 02B MOVES AWAY FROM THE GRADIENT LEVEL
WESTERLIES AND UPPER LEVEL DIVERGENCE ASSOCIATED WITH THAT
STIMULUS, THE WEAKER ASANI WILL BECOME.

INITIAL WIND RADII BASIS: PERSISTENCE. 

CURRENT STEERING MECHANISM: A MID LEVEL RIDGE EXTENDING FROM THE
MALAY PENINSULA ALONG THE EAST COAST OF THAILAND AND MYANMAR. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   CIMSS SATCON: 58 KTS AT 092011Z
   CIMSS ADT: 72 KTS AT 100015Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 02B WILL GRADUALLY WEAKEN AND TURN TO AN
INCREASINGLY POLEWARD TRACK OVER THE 36 HOURS, APPROACHING THE
INDIAN COAST BETWEEN GUDIVADA AND VISHAKHAPATNAM.  ALTHOUGH SURFACE
WATERS WILL REMAIN WARM, A SHARP DROP IN OCEAN HEAT CONTENT ALONG
TRACK WILL COMBINE WITH DRIER OFF-SHORE FLOW AND INCREASING
VERTICAL WIND SHEAR TO DETERIORATE THE SYSTEM BEFORE IT REACHES
BANGLEDESH, LEAVING A WEAK LOW LEVEL VORTEX DRIFTING IN THE
NORTHERN BOB. DESPITE ITS DISSIPATION OVER WATER HOWEVER, ASANI
WILL HAVE MANAGED TO LOCK IN THE SOUTHWEST MONSOON OVER THE BOB FOR
THE SEASON. 

MODEL DISCUSSION: MODEL GUIDANCE PERFORMED REMARKABLY IN PREDICTING
THE FORMATION OF TC 02B AND 25S FROM NEARLY 10 DAYS OUT, ESPECIALLY
GFS. OVER THE PAST 72 HOURS THE TRACK GUIDANCE HAS SHFTED TOWARDS A
MORE WESTWARD TRACK SHOWING A LESS EMPHATIC RECURVATURE TOWARDS THE 
NORTHERN BOB. NOW THE ECMWF ENSEMBLE IS SHOWING A BIFURCATED
TRACK, WITH SOME MEMBERS GOING ASHORE OVER COASTAL INDIA. THE 
ENSEMBLE MEAN AND DETERMINISTIC TRACKER STILL TURN THE STORM 
POLEWARD, HOWEVER. THE JTWC FORECAST STAYS TO THE RIGHT OF CONSENSUS 
FAVORING THE MORE SKILLFUL MODELS. ALTHOUGH THE INTENSITY GUIDANCE 
DID NOT QUITE CAPTURE THE RECENT SURGE UP TO TYPHOON STRENGTH, IT HAS 
BEEN CONSISTENT AND REFLECTED THE TRENDS ACCURATELY AND THE DEVIATION 
AMONGST THE VARIOUS MEMBERS IS CONSIDERABLY LESS THAN AVERAGE. THE 
JTWC INTENSITY FORECAST STAYS ALONG THE MULTI-MODEL ENSEMBLE MEAN.   

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
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