WDIO31 PGTW 190900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (FOUR) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.0N 89.1E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 104 NM SOUTH-SOUTHEAST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
CONSOLIDATING SYSTEM WITH CONVECTIVE BANDING WRAPPING TIGHTLY INTO
A WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). MSI ALSO SHOWS
EXTENSIVE, FRAGMENTED SPIRAL BANDING OVER THE SOUTHERN SEMICIRCLE.
A 190334Z AMSU-B 89GHZ MICROWAVE IMAGE REVEALS CURVED INNER
CONVECTIVE BANDS OVER THE NORTHWEST AND SOUTHEAST QUADRANTS
SURROUNDING A DEFINED LLCC, WHICH ALSO SUPPORTS THE INITIAL
POSITION WITH HIGH CONFIDENCE. THE RECENT NORTHWESTWARD TURN
BROUGHT THE CENTER CLOSE TO SUNDARBAN NATIONAL PARK, ON THE
BANGLADESH, INDIA BORDER, HOWEVER SURFACE OBSERVATIONS ARE
UNAVAILABLE IN THIS REGION. THE INITIAL INTENSITY OF 45 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PGTW AND KNES DVORAK
ESTIMATES. ADT ESTIMATES HAVE INCREASED TO ABOUT 40 KNOTS WITH THE
RAW T NUMBERS SLIGHTLY HIGHER AT 41-45 KNOTS. TC 04B HAS BEEN ABLE
TO CONSOLIDATE DESPITE FAIRLY STRONG EASTERLY FLOW ALOFT AND HAS
DEVELOPED IMPROVED OUTFLOW OVER THE EASTERN QUADRANT IN ADDITION TO
VIGOROUS EQUATORWARD OUTFLOW. AS THE MODELS PREDICTED, VERTICAL
WIND SHEAR HAS DECREASED TO LOW TO MODERATE LEVELS.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR) POSITIONED TO THE NORTH AND NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   DEMS: T1.5 - 25 KTS
   CIMSS ADT: 39 KTS AT 190645Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 IS EXPECTED TO TRACK GENERALLY
WEST-NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR TO THE
NORTH WHILE MAINTAINING INTENSITY AT 45 KNOTS THROUGH TAU 12. SLIGHT
INTENSIFICATION COULD OCCUR BEFORE LANDFALL NEAR TAU 12 IF THE
SYSTEM TRACKS SOUTH OF THE COAST. AFTER TAU 12, THE SYSTEM WILL
TRACK INLAND AND RAPIDLY DISSIPATE.  

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT
AGREEMENT WITH A 15 NM (TAU 12) TO 40NM (TAU 24) SPREAD IN
SOLUTIONS LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK.
INTENSITY GUIDANCE SUPPORTS A GRADUAL WEAKENING TREND THROUGH TAU
12 WITH DECAY SHIPS (GFS VERSION), THE SOLE OUTLIER, INDICATING A
PEAK TO 50 KNOTS AT TAU 12. AFTER TAU 12, INTENSITY GUIDANCE IS IN
TIGHT AGREEMENT ON THE RAPID WEAKENING PHASE.   

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