WDIO31 PGTW 182100
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: 20.5N 89.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 151 NM SOUTHEAST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A MASS
OF BUILDING CONVECTION OVER AN ASSESSED LOW LEVEL CIRCULATION (LLC)
TRACKING WEST-NORTHWEST OVER THE NORTHERN BAY OF BENGAL. AN 181859Z
37 GHZ GMI PASS INDICATES AN CONSOLIDATING SYSTEM WITH FRAGMENTED
BANDING WRAPPING INTO THE CENTER OF THE LLC IN THE NORTHEAST AND
SOUTHWEST QUADRANTS. THIS PASS ALSO INDICATES A MAJORITY OF THE
CONVECTIVE ACTIVITY TO BE IN THE SOUTHERN PERIPHERY. ENVIRONMENTAL
ANALYSIS INDICATES TC 04B IS IN A MARGINAL AREA FOR FURTHER
DEVELOPMENT WITH STRONG UPPER LEVEL OUTFLOW, A HIGH MAGNITUDE 850 MB
SIGNATURE, AND WARM (29-30 C) SEA SURFACE TEMPERATURES, OFFSET BY
STRONG (25-30 KTS) VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION
IS PLACED WITH MEDIUM CONFIDENCE BASED ON MULTIPLE AGENCY FIXES,
PARTIAL RADAR IMAGERY FROM KOLKATA, INDIA AND THE AFOREMENTIONED
EIR DATA. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON PGTW DVORAK ESTIMATE, SET SLIGHTLY HIGHER THAN
KNES AND DEMS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA FROM 180359Z.

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   DEMS: T1.0 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG WESTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 04B IS ON A DIRECT PATH TO MAKE LANDFALL 74
NM TO THE SOUTHWEST OF KOLKATA ALONG THE COAST OF NORTHEAST INDIA.
THE INTENSITY WILL STEADILY INCREASE TO 45 KNOTS BY TAU 12 AS THE
VERTICAL WIND SHEAR IS EXPECTED TO DECREASE DUE TO A BREAK IN THE
UPPER LEVEL WINDS OVER THE NEXT 24 HOURS. THE INTENSITY IS EXPECTED
TO REACH A MAXIMUM OF 50 KNOTS JUST BEFORE LANDFALL DUE TO THE
OVERALL IMPROVEMENT OF THE ENVIRONMENT AS THE SYSTEM TRACKS
WEST-NORTHWEST. BY TAU 24 TC 04B WILL DECREASE IN INTENSITY TO 40
KNOTS AND BEGIN DISSIPATION DUE TO LAND INTERACTION AFTER LANDFALL.
BY TAU 36 THE SYSTEM WILL BE DISSIPATED WITH THE INTENSITY FALLING
TO 30 KNOTS.

MODEL DISCUSSION: THE JTWC TRACK CONSENSUS ENVELOPE IS RELATIVELY
TIGHT WITH A GRADUAL SPREAD TO 27 NM BY TAU 12, DECREASING TO 14 NM
AFTER LANDFALL BY TAU 24. DUE TO THIS TIGHT ENVELOPE THE CONFIDENCE
IN THE JTWC FORECAST TRACK IS HIGH. INTENSITY GUIDANCE IS IN RATHER
GOOD AGREEMENT WITH A 10-15 KNOT SPREAD AT TAU 12, WITH HWRF AND 
COAMPS-TC BEING THE MOST AGGRESSIVE. THIS COUPLED WITH THE IMPROVING 
ENVIRONMENT OVER THE NEXT 24 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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