WDIO31 PGTW 190300
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: 20.8N 89.1E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 115 NM SOUTH-SOUTHEAST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A MASS
OF BUILDING CONVECTION OVER THE SOUTHERN PERIPHERY OF AN ASSESSED
LOW LEVEL CIRCULATION (LLC) TRACKING WEST-NORTHWEST OVER THE
NORTHERN BAY OF BENGAL. AN 182313Z 91 GHZ SSMIS PASS SHOWS
FRAGMENTED BANDING IN THE WESTERN AND SOUTHERN QUADRANTS WRAPPING
INTO THE CENTER OF THE LLC. THIS PASS ALSO INDICATES A MAJORITY OF
THE CONVECTIVE ACTIVITY TO BE IN THE SOUTHERN PERIPHERY AS WELL AS IN 
THE OUTER BAND THAT STRETCHES NORTHWEST TO NORTHEAST OF KOLKATA, 
INDIA. ENVIRONMENTAL ANALYSIS INDICATES TC 04B IS IN A MARGINALLY
FAVORABLE AREA FOR FURTHER DEVELOPMENT WITH SPLIT WESTWARD AND
EQUATORWARD UPPER LEVEL OUTFLOW, A HIGH MAGNITUDE 850 MB SIGNATURE,
AND WARM (29-30 C) SEA SURFACE TEMPERATURES, OFFSET BY MODERATE
(15-20 KTS) VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON MULTIPLE AGENCY FIXES,
PARTIAL RADAR IMAGERY FROM KOLKATA AND THE AFOREMENTIONED
EIR DATA. THE INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE SET LOWER THAN THE PGTW DVORAK ESTIMATE AND HIGHER THAN
AUTOMATED AND OTHER AGENCY DVORAKS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 35 KTS AT 182115Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG WESTWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 04B CONTINUES ON A DIRECT PATH TO MAKE 
LANDFALL ALONG THE COAST OF NORTHEAST INDIA APPROXIMATELY 75
NM SOUTHWEST OF KOLKATA. THE INTENSITY WILL STEADILY INCREASE TO 45 
KNOTS BY TAU 12 DURING LANDFALL AS THE VERTICAL WIND SHEAR IS 
EXPECTED TO CONTINUE TO DECREASE DUE TO A BREAK IN THE UPPER LEVEL 
WINDS OVER THE NEXT 18 HOURS. BY TAU 24 TC 04B WILL DECREASE IN 
INTENSITY TO 35 KNOTS AND BEGIN DISSIPATION DUE TO LAND INTERACTION.
BY TAU 36 THE SYSTEM WILL BE DISSIPATED WITH THE INTENSITY FALLING
TO 30 KNOTS.

MODEL DISCUSSION: THE JTWC TRACK CONSENSUS ENVELOPE CONTINUES TO BE
RELATIVELY TIGHT AIMING NORTHWESTWARD WITH NAVGEM BEING THE OUTLIER
WITH A JOG WESTWARD IMMEDIATELY OUT TO TAU 12, THEN EASING INTO A 
MORE WEST-NORTHWESTWARD DIRECTION AFTERWARDS. DUE TO THIS OUTLIER THE
JTWC FORECAST TRACK IS SET SLIGHTLY TO THE RIGHT OF TRACK WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE IS IN BETTER AGREEMENT THAN THE 
PREVIOUS MODEL RUN WITH A 5-10 KNOT SPREAD AT TAU 12. THIS IMPROVED 
AGREEMENT COUPLED WITH THE IMPROVING ENVIRONMENT OVER THE NEXT 18 
HOURS LENDS MEDIUM CONFIDENCE IN THE JTWC INTENSITY FORECAST WHICH IS 
SET SLIGHTLY HIGHER THAN CONSENSUS.

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