WDIO31 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 02B (ASANI) WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.4N 85.5E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 519 NM SOUTH-SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
IMPROVED CONVECTIVE STRUCTURE WITH A CENTRAL DENSE OVERCAST (CDO)
OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC), WHICH IS
POSITIONED UNDER THE NORTHEASTERN EDGE OF THE CDO. A 090739Z ATMS
88.2GHZ MICROWAVE IMAGE REVEALS EXPOSED SHALLOW BANDING OVER THE
EASTERN SEMICIRCLE WITH CURVED DEEP CONVECTIVE BANDING SHEARED OVER
THE SOUTHWESTERN QUADRANT. ENVIRONMENTAL CONDITIONS REMAIN
MARGINALLY FAVORABLE WITH HIGH (25 KNOTS) EASTERLY VERTICAL WIND
SHEAR (VWS) OFFSET BY MODERATE WESTWARD OUTFLOW. ANIMATED WATER
VAPOR IMAGERY INDICATES POLEWARD OUTFLOW HAS EFFECTIVELY CEASED
OVER THE PAST SIX HOURS. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE ATMS IMAGE AND EIR IMAGERY. THE INITIAL
INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
CIMSS ADT ESTIMATE AND RECENT AIDT ESTIMATES AROUND 62 KNOTS.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHWEST PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   DEMS: T3.5 - 55 KTS
   CIMSS ADT: 59 KTS AT 090615Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE TAU 24 TO TAU 72 PORTION OF THE
FORECAST TRACK HAS SHIFTED CLOSER TO THE INDIAN COAST WITH
SIGNIFICANTLY SLOWER TRACK SPEEDS.

FORECAST DISCUSSION: OVER THE PAST TWO DAYS, THE STR HAS REMAINED
ENTRENCHED TO THE NORTHEAST. PREVIOUS MODEL GUIDANCE HAD INDICATED
THE STR WOULD ERODE AS A MIDLATITUDE TROUGH DEEPENED TO THE NORTH
ALLOWING THE SYSTEM TO RECURVE. UPPER-LEVEL ANALYSIS DOES INDICATE
A WEAK TROUGH OVER NORTHEAST INDIA, BARELY DISCERNIBLE IN ANIMATED
WATER VAPOR IMAGERY, HOWEVER THE TROUGH IS FORECAST TO PROPAGATE
EASTWARD WITH LITTLE EFFECT ON THE STRENGTH OF THE STR. THE CURRENT
FORECAST INDICATES THE SYSTEM WILL CONTINUE TO TRACK NORTHWESTWARD
SLOWLY TURNING POLEWARD NEAR VISAKHAPATNAM BY TAU 48 WITHIN A
COMPETING STEERING ENVIRONMENT. TC 02B WILL WEAKEN STEADILY DURING
THIS PERIOD UNDER PERSISTENT EASTERLY VWS (25-30 KNOTS) AND
INTERACTION WITH LAND. AFTER TAU 48, UPPER-LEVEL WESTERLIES ARE
EXPECTED TO PUSH INTO THE BAY OF BENGAL WITH THE STR WEAKENING AND
SHIFTING EAST. THIS SHOULD ALLOW THE SYSTEM TO ACCELERATE
NORTHEASTWARD TOWARD BANGLADESH ALONG THE NORTHWESTERN PERIPHERY OF
THE STR. TC 02B WILL BE EMBEDDED WITHIN THE UPPER-LEVEL WESTERLIES
IN A MARGINAL ENVIRONMENT AND IS EXPECTED TO CONTINUE TO WEAKEN AND
EVENTUALLY DISSIPATE OVER THE NORTHERN BAY OF BENGAL.   

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE CONTINUES TO STRUGGLE
WITH THIS COMPLEX STEERING ENVIRONMENT WITH SIGNIFICANT UNCERTAINTY
IN THE JTWC FORECAST TRACK. IN GENERAL, MODEL GUIDANCE IS IN POOR
AGREEMENT AND SHOWS A LARGE SPREAD IN SOLUTIONS AFTER TAU 48. THE
090000Z ECMWF ENSEMBLE (EPS), WHICH HAS HANDLED THE SCENARIO FAIRLY
WELL THUS FAR, IS NOW INDICATING A BIFURCATION WITH LANDFALL NEAR
VISAKHAPATNAM AND DISSIPATION OR A SHARP NORTHEASTWARD RECURVE AND
TRACK ALONG THE COAST OF NORTHEAST INDIA AND EVENTUAL DISSIPATION
NEAR BANGLADESH. THE BULK OF THE RELIABLE INTENSITY GUIDANCE
INDICATES GOOD AGREEMENT ON STEADY WEAKENING WITH A WEAK TROPICAL
CYCLONE IN THE EXTENDED PERIOD THUS OVERALL MEDIUM CONFIDENCE. 
MODEL GUIDANCE DOES INDICATE, HOWEVER, SIGNIFICANT RAINFALL
SPREADING ACROSS EASTERN INDIA AND THE NORTHERN BAY OF BENGAL
INTO BANGLADESH AND MYANMAR.  
      
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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