WDIO31 PGTW 301500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (FENGAL) WARNING 
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.4N 80.6E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 757 NM SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 04B (FENGAL) WITH FRAGMENTED CONVECTIVE BANDING ALONG THE
NORTHERN SEMICIRCLE OF A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC). THE OVERALL CONVECTIVE STRUCTURE HAS SLIGHTLY
DEGRADED OVER THE PAST 6 HOURS AS HIGH EASTERLY VERTICAL WIND SHEAR
CONTINUES TO INTERACT WITH THE SYSTEM. THE LLCC IS ANALYZED TO BE
ABOUT 30 NM OFF THE COAST OF INDIA, OFFSET TO THE EAST OF THE
CONVECTIVE BURSTS. ENVIRONMENTAL ANALYSIS INDICATES THAT 04B IS IN
A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD
OUTFLOW ALOFT, HIGH (25-30 KTS) VERTICAL WIND SHEAR, AND WARM
(27-28 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON ANIMATED RADAR IMAGERY AND THE
PARTIALLY EXPOSED LLCC IN THE ANIMATED MSI. THE INITIAL INTENSITY
OF 45 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY
DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF AN EXTENSION OF A
SUBTROPICAL RIDGE (STR) TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS ADT: 51 KTS AT 301200Z
   CIMSS AIDT: 39 KTS AT 301200Z
   CIMSS DPRINT: 47 KTS AT 301200Z
   CIMSS DMINT: 54 KTS AT 301050Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 25-30 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: INITIAL TERRAIN INTERACTION

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: 04B IS FORECAST TO CONTINUE TRACKING SLOWLY
WESTWARD, ALONG THE SOUTHERN PERIPHERY OF AN EXTENSION OF THE STR
TO THE EAST AS THE SYSTEM INCHES CLOSER TO THE COAST OF
SOUTHEASTERN INDIA. LANDFALL IS EXPECTED TO OCCUR IN AROUND 12-18
HOURS. 04B IS FORECAST TO GRADUALLY WEAKEN AS IT APPROACHES THE
COAST DUE TO THE HIGH VERTICAL WIND SHEAR AND INCREASING TERRAIN
INTERACTION. AN INTENSITY NEAR 40 KTS IS EXPECTED AT THE TIME OF
LANDFALL AND THEN FURTHER WEAKENING AFTERWARD. TERRAIN INTERACTION
WILL CONTINUE TO ERODE THE VORTEX AND CAUSE THE INTENSITY TO DROP
TO BELOW TROPICAL STORM STRENGTH AROUND TAU 36. 

MODEL DISCUSSION: GFS CONTINUES TO BE THE MAIN OUTLIER WITH A STALL
OFF THE COAST THROUGH TAU 48. THE REMAINDER OF RELIABLE GUIDANCE
SUGGESTS THE SLOW WESTWARD TRACK. THE JTWC TRACK FORECAST IS PLACED
WITHIN THE MAIN ENVELOPE OF GUIDANCE WITH MEDIUM CONFIDENCE. THE
SCENARIO OF A STALL OFF THE COAST SHOULD NOT BE COMPLETELY
DISCOUNTED THOUGH AS THE OVERALL STEERING PATTERN IS RELATIVELY
WEAK. IF THE EXTENSION OF THE STR LOSES INFLUENCE ON THE VORTEX, IT
COULD STALL BEFORE THE RIDGING BUILDS BACK UP AND PUSHES THE SYSTEM
INLAND. INTENSITY GUIDANCE IS IN BETTER AGREEMENT WITH ALL MODELS
SUGGESTING A CONTINUED WEAKENING TREND THROUGHOUT THE FORECAST
PERIOD. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO CONSENSUS
WITH HIGH CONFIDENCE. 

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