Advisories

WDIO31 PGTW 010300
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: 11.6N 86.6E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 668 NM SOUTH OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL 
CYCLONE (TC) 04B WITH A PERSISTENT CENTRAL DENSE OVERCAST (CDO)
OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC) AND DEVELOPING
CONVECTIVE BANDING ON THE NORTHERN AND SOUTHERN SIDES. A 312225Z
SSMIS 91 GHZ MICROWAVE IMAGE DEPICTS DEEP CONVECTION OFFSET TO THE
NORTHWEST OF THE ASSESSED LLCC. ENVIRONMENTAL CONDITIONS ARE ASSESSED 
AS FAVORABLE WITH LOW (5-10 KTS) VERTICAL WIND SHEAR, WARM (29-30 C) 
SEA SURFACE TEMPERATURES, AND STRONG RADIAL AND WESTWARD OUTFLOW 
ALOFT. THE INITIAL POSITION IS ASSESSED WITH LOW CONFIDENCE BASED ON 
THE OBSCURED LLCC. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM 
CONFIDENCE BASED ON THE AGENCY DVORAK FIXES. THE INITIAL WIND RADII 
ARE ASSESSED WITH LOW CONFIDENCE BASED ON PERSISTENCE FROM A 311736Z 
OSCAT PASS.

INITIAL WIND RADII BASIS: OSCAT DATA

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE
NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   DEMS: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 04B IS FORECAST TO TRACK NORTHWESTWARD FOR THE 
ENTIRETY OF THE FORECAST PERIOD UNDER THE INFLUENCE OF A SUBTROPICAL 
RIDGE (STR) CENTERED TO THE NORTHEAST. TRACK SPEED WILL SLOW AS IT 
APPROACHES EASTERN INDIA, WITH LANDFALL EXPECTED TO OCCUR BETWEEN TAUS 
36 AND 48. TRACK SPEED WILL SLOW AS THE SYSTEM INTERACTS WITH THE 
TERRAIN. REGARDING INTENSITY, TC 04B IS EXPECTED TO INTENSIFY OUT TO A 
PEAK OF 50 KTS BETWEEN TAUS 24 AND 36 AS ENVIRONMENTAL CONDITIONS 
REMAIN FAVORABLE AND THE SYSTEM CONTINUES TO CONSOLIDATE. AFTER THIS 
POINT, IT IS EXPECTED TO SHARPLY WEAKEN ONCE IT MAKES LANDFALL AND 
TERRAIN INTERACTION DETERIORATES THE VORTEX. 

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGHOUT 
THE FORECAST PERIOD, WITH AN 85 NM CROSS-TRACK SPREAD AT THE TIME OF 
LANDFALL. AFTER LANDFALL, THE MAJORITY OF MODELS SLOW IN TRACK SPEED 
AND DEPICT A SLIGHT WESTWARD TURN. THE OFFICIAL JTWC FORECAST TRACK IS 
ASSESSED WITH HIGH CONFIDENCE, IN GOOD AGREEMENT WITH BOTH THE MULTI-
MODEL AND AI CONSENSUS. INTENSITY MODEL GUIDANCE IS QUITE SPREAD, WITH 
COAMPS-TC, HWRF, AND DECAY-SHIPS DEPICTING PEAKS OF 55 TO 65 KTS AT 
TAU 36 WHILE GFS SHOWS ONLY 40 KTS AT THIS TIME. THE DECAY SHIPS 
MODELS ARE THE SLOWEST TO SHOW DISSIPATION AT TAU 72, WITH THE 
MAJORITY OF MODELS DISSIPATING 04B BY TAU 60. THE FORECAST IS THUS 
EXTENDED OUT TO TAU 72 TO ALLOW FOR THE POSSIBLE SLOWER DISSIPATION AS 
DECAY SHIPS IS SKILLED IN LANDFALL FORECASTS, ALTHOUGH DUE TO ITS 
HIGHER PEAK, THE OFFICIAL JTWC DEPICTS DISSIPATION PRIOR TO TAU 72. A 
RAPID INTENSIFICATION (RI) AID HAS ALSO POPULATED, THOUGH NOT DEPICTED 
IN THE FORECAST. MODELS ARE IN GOOD AGREEMENT ON THE SHARP WEAKENING 
AND DISSIPATION FOLLOWING LANDFALL BUT RETAIN A 20 KT SPREAD DUE TO 
THE DIFFERENT FORECAST PEAKS. THE OFFICIAL JTWC INTENSITY FORECAST IS 
THUS ASSESSED WITH LOW CONFIDENCE, IN GOOD AGREEMENT WITH THE
MULTI-MODEL CONSENSUS.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: LOW//
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