WDIO31 PGTW 240900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 05B (SITRANG)      
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.3N 89.7E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 215 NM SOUTHWEST OF CHITTAGONG, BANGLADESH
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 05B IS A LARGE 500-600NM DIAMETER SYSTEM WITH
EXTENSIVE GALE-FORCE WINDS AND A SWATH OF 35-40 KNOT WINDS OVER THE
NORTHWEST QUADRANT. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC)
WITH A LARGE REGION OF INTENSE DEEP CONVECTION PERSISTING OVER THE
NORTHERN SEMICIRCLE. UPPER-LEVEL ANALYSIS SHOWS STRONG DIFFLUENT
FLOW BETWEEN A SHARP UPPER-LEVEL TROUGH OVER CENTRAL INDIA AND A
BROAD ANTICYCLONE TO THE EAST NEAR 20N 94E. WINDS WITHIN THIS WEDGE
OF DIFFLUENT UPPER-LEVEL FLOW RANGE FROM 50-70 KNOTS, WHICH IS
FUELING THE INTENSE CONVECTION ACROSS NORTHEAST INDIA AND
BANGLADESH. A 240034Z SSMIS 91GHZ MICROWAVE IMAGE REVEALS A BROAD,
SHALLOW LLCC WITH DEEP CONVECTIVE BANDING SHEARED TO THE
NORTH-NORTHWEST WITH ANOTHER REGION OF DEEP CONVECTION OVER
BANGLADESH. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON EXTRAPOLATION FROM THE ASCAT-B IMAGE. THE INITIAL
INTENSITY OF 40 KTS IS HEDGED ABOVE THE DVORAK ESTIMATES BASED ON
THE ASCAT-B DATA AND IS ASSESSED WITH HIGH CONFIDENCE. THE 34-KNOT
WIND RADII HAVE BEEN ADJUSTED BASED ON A DETAILED ANALYSIS OF THE
240413Z ASCAT-B IMAGE AND REFLECT EXTENSIVE GALE-FORCE WINDS OVER
THE EASTERN AND NORTHERN SEMICIRCLES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
ENTRENCHED TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 45 KTS AT 240315Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 05B IS FORECAST TO
CONSOLIDATE THROUGH TAU 12 UNDER FAVORABLE CONDITIONS AS IT TRACKS
POLEWARD ALONG THE WESTERN PERIPHERY OF THE NORTH-SOUTH ORIENTED
STR. AFTER TAU 12, INTERACTION WITH LAND AND INCREASING VERTICAL
WIND SHEAR WILL CONTRIBUTE TO A STEADY WEAKENING TREND AND EVENTUAL
DISSIPATION OVER BANGLADESH BY TAU 36. HOWEVER, THE LARGE SYSTEM IS
EXPECTED TO PRODUCE HEAVY RAINFALL ACROSS BANGLADESH, INCLUDING THE
EASTERN REGION NEAR CHITTAGONG AND COX'S BAZAR.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT
WITH A 25-55NM CROSS-TRACK SPREAD IN SOLUTIONS AT TAU 12 TO TAU 24.
ADDITIONALLY, THE 240000Z ECMWF (EPS) AND GFS (GEFS) ENSEMBLES ARE
IN TIGHT AGREEMENT WITH A TRACK OVER THE SOUTHEASTERN COAST OF
BANGLADESH. THUS, THERE IS HIGH CONFIDENCE IN THE JTWC TRACK
FORECAST. THE 231800Z COAMPS-TC ENSEMBLE INDICATES AN 80-100
PERCENT PROBABILITY OF A STRONG TROPICAL STORM-STRENGTH (50-63
KNOTS) SYSTEM DEVELOPING WITHIN THE NEXT SIX HOURS. RELIABLE
INTENSITY GUIDANCE CURRENTLY PEAKS AT 40 KNOTS WITH A SLIGHT
WEAKENING TREND THROUGH TAU 12, HOWEVER, THE JTWC INTENSITY
FORECAST IS HEDGED HIGHER THAN THE GUIDANCE FOR NOW IN
CONSIDERATION OF THE ASCAT-B DATA AND THE 12-HOUR WINDOW FOR
FURTHER DEVELOPMENT BEFORE LANDFALL.  

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