WDIO31 PGTW 010300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (FOUR) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.9N 91.7E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 84 NM SOUTH OF CHITTAGONG
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN EXPOSED
LOW LEVEL CIRCULATION CENTER (LLCC) WITH SPOTTY CONVECTION FLARING
UP ON THE WESTERN AND SOUTHERN SIDES OF THE CIRCULATION. ANIMATED
RADAR DATA FROM BANGLADESH SHOWS THE LLCC TO GOOD EFFECT, AND
COMBINED WITH THE MSI IMAGERY, PROVIDED HIGH CONFIDENCE TO THE
INITIAL POSITION. THE INITIAL INTENSITY REMAINS SET AT 40 KNOTS
WITH MEDIUM CONFIDENCE, HEDGED SLIGHTLY HIGHER THAN THE AGENCY
DVORAK INTENSITY ESTIMATES OF T2.0 (30 KNOTS) FROM BOTH PGTW AND
KNES, IN PERSISTENCE WITH EARLIER SCATTEROMETER DATA. CIMSS
ANALYSIS REVEALS A SIGNIFICANT INCREASE IN NORTHEASTERLY SHEAR, NOW
UP TO 25-30 KNOTS, BUT THE UPPER-LEVEL FLOW REMAINS DIVERGENT IN
THE VICINITY OF THE CIRCULATION, PROVIDING SOME EXHAUST FOR THE
FLARING CONVECTION. OUTSIDE OF THE SHEAR, THE ENVIRONMENT REMAINS
SUPPORTIVE, WITH VERY WARM SSTS AND ROBUST EQUATORWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   DEMS: T1.0 - 25 KTS
   CIMSS ADT: 41 KTS AT 312330Z

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 04B (FOUR) IS FORECAST
TO TRACK NORTHWESTWARD ALONG THE WESTERN SIDE OF THE STEERING
RIDGE, WITH LANDFALL EXPECTED WITHIN THE NEXT 12 HOURS IN THE
VICINITY OF KUAKATA, BANGLADESH. NO SIGNIFICANT CHANGE IN THE
INTENSITY ARE EXPECTED, WITH LANDFALL AT OR NEAR 40 KNOTS. AFTER
LANDFALL, THE SYSTEM WILL TRACK GENERALLY WEST-NORTHWEST WHILE
SLOWLY WEAKENING DUE TO LAND INTERACTION, BEFORE DISSIPATING OVER
EASTERN INDIA NO LATER THAN TAU 36. 

MODEL DISCUSSION: AVAILABLE TRACK GUIDANCE IS IN GOOD AGREEMENT
THROUGH THE FORECAST PERIOD, PROVIDING HIGH CONFIDENCE TO THE JTWC
FORECAST TRACK. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT,
THOUGH THE JTWC FORECAST DEVIATES ABOUT FIVE KNOTS HIGHER IN THE
FIRST 12 HOURS, BUT OTHERWISE ALIGNS WELL WITH THE GUIDANCE
PACKAGE, WITH HIGH CONFIDENCE. 

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