WDIO31 PGTW 312100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (FOUR) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.0N 92.0E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 138 NM SOUTH OF CHITTAGONG
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
EXPOSED BUT WELL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) JUST
WEST OF SITTWE, MYANMAR. THE FIRST HINTS OF THE ROTATION ARE ALSO
BECOMING EVIDENT IN THE ANIMATED RADAR DATA OUT OF BANGLADESH. THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
EXPOSED LLCC IN THE EIR AND PROXY VISIBLE IMAGERY. WHILE AGENCY
DVORAK CURRENT INTENSITY FIXES ARE RELATIVELY LOW, IN THE T1.0 TO
T2.0 RANGE, TWO EARLIER ASCAT PASSES AT 311440Z AND 311528Z SHOWED
A WEDGE OF 35-40 KNOT WINDS ACROSS THE SOUTHERN HEMISPHERE OF THE
CIRCULATION, WITH THE HIGHEST WINDS IN THE SOUTHEAST QUADRANT. THE
SCATTEROMETER DATA LENT HIGH CONFIDENCE TO THE INTENSITY ESTIMATE,
WELL ABOVE THE DVORAK-BASED ESTIMATES. THE EIR ALSO SHOWS
DISORGANIZED CONVECTION DISPLACED AWAY FROM THE LLCC DUE TO
PERSISTENT LOW TO MODERATE NORTHEASTERLY SHEAR. BIT UPPER-LEVEL
WINDS ASSOCIATED THE TROPICAL EASTERLY JET (TEJ) APPEAR TO HAVE
WEAKENED JUST ENOUGH TO ALLOW FOR THE SYSTEM TO CONSOLIDATE AND
INTENSIFY. CONDITIONS ARE MARGINAL, WITH WARMS SSTS, AND GOOD
EQUATORWARD OUTFLOW OFFSET BY MODERATE TO HIGH NORTHEASTERLY SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF THE LOW TO
MID-LEVEL SUBTROPICAL RIDGE (STR) OVER CHINA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   DEMS: T1.0 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 04B (FOUR) WILL BE
SHORT-LIVED, AS IT TRACKS QUICKLY TO THE NORTH-NORTHWEST THROUGH
THE FORECAST PERIOD. LANDFALL IS CURRENTLY ANTICIPATED ON THE COAST
OF BANGLADESH WITHIN THE NEXT 24 HOURS, AND AFTER LANDFALL THE
SYSTEM WILL RAPIDLY MOVE INLAND TOWARDS THE VICINITY OF KOLKATA.
WHILE THE SYSTEM HAS ENJOYED A BRIEF PERIOD OF LOW TO MODERATE
SHEAR, WHICH ALLOWED IT TO INTENSIFY TO TC STRENGTH, ANOTHER PULSE
OF TEJ-ASSOCIATED NORTHEASTERLY FLOW WILL MOVE IN WITHIN THE NEXT
FEW HOURS AND SERVE TO SQUASH TC 04B AS IT TRACKS NORTHWARD.
HOWEVER, DUE TO ALREADY STRONG VORTICITY WHICH HAS DEVELOPED
INDEPENDENT OF ANY ORGANIZED CONVECTION, ENHANCED BY SOME
TERRAIN-INDUCED COMPRESSION ON THE EASTERN SIDE, THE SYSTEM WILL
LIKELY MAKE LANDFALL AS A 35 TO 40 KNOT TROPICAL CYCLONE. RAPID
WEAKENING AND DISSIPATION IS EXPECTED BY TAU 36 OVER SOUTHEAST
INDIA. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN TIGHT AGREEMENT ON A
NORTHWEST TRACK THROUGH LANDFALL, CURVING TO WESTWARD AFTER TAU 24,
LENDING HIGH CONFIDENCE TO THE JTWC FORECAST. INTENSITY GUIDANCE IS
ALSO IN GOOD AGREEMENT THAT THE SYSTEM WILL MAINTAIN INTENSITY
THROUGH LANDFALL AND QUICKLY DISSIPATE THEREAFTER. 

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