WDIO31 PGTW 050300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 01B (ONE) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.8N 84.3E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 689 NM SOUTH-SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A STEADY
AREA OF CONVECTION OVER AN ASSESSED LOW LEVEL CIRCULATION CENTER
(LLCC). A 042254Z SSMIS 91GHZ MICROWAVE IMAGE DEPICTS LOW LEVEL
BANDING WITH AREAS OF CONVECTION ON THE WESTERN AND EASTERN
PERIPHERIES OF THE LLCC. OTHER SCATTEROMETRY DATA REVEALS A
RELATIVELY SYMMETRICAL CIRCULATION WITH 30-35KT WINDS IN THE
NORTHWEST QUADRANT. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON PGTW FIX, EIR AND MICROWAVE IMAGERY. THE
INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON AFOREMENTIONED SCATTEROMETRY DATA, PGTW AND AUTOMATED
DVORAKS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) LOCATED TO THE
EAST-NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   DEMS: T2.0 - 30 KTS
   CIMSS ADT: 37 KTS AT 042115Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND WESTWARD

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 01B IS CURRENTLY TRACKING NORTHEAST UNDER
THE STEERING INFLUENCE OF A STR, UNLIKE PREVIOUSLY FORECAST THE
SYSTEM HAS NOT YET TURNED TOWARD THE MAINLAND OF SOUTHEASTERN
INDIA. HOWEVER, BY TAU 12, AS THE STR CONTINUES TO BUILD IN FROM
THE NORTHEAST, THE SYSTEM WILL BE FORCED TO TRACK WEST-
SOUTHWESTWARD. TC 01B IS FORECAST TO REACH A PEAK INTENSITY OF 40 
KNOTS WHILE STILL IN A MARGINAL ENVIRONMENT CHARACTERIZED BY WARM 
(27-28 C) SEA SURFACE TEMPERATURES (SST), LOW (5-10 KTS) VERTICAL 
WINDS SHEAR (VWS) AND GOOD POLEWARD AND WESTWARD OUTFLOW, OFF SET BY 
WEAK DRY AIR ENTRAINMENT. BETWEEN TAU 12 AND 36, SIGNIFICANT DRY AIR 
ENTRAINMENT, INCREASING VWS AND LAND INTERACTION WILL STEADILY 
WEAKEN TC 01B. BY TAU 48, THE INTENSITY IS FORECAST TO FALL BELOW 25 
KNOTS AS ITS MID AND UPPER LEVELS BECOME FULLY ENTRAINED BY DRY AIR 
AFTER WHICH FULL DISSIPATION IS EXPECTED.

MODEL DISCUSSION: AS THE STR BUILDS TO THE NORTHEAST NUMERICAL
MODEL GUIDANCE IS IN GOOD AGREEMENT ABOUT THE FORECAST TRACK WITH A
40NM SPREAD IN SOLUTIONS AT TAU 48. THE JTWC FORECAST TRACK IS
PLACED WITH MEDIUM CONFIDENCE BASED ON THE MODERATE MODEL SPREAD
AND THE UNCERTAINTY OF THE TIMING OF WHEN THE RIDGE TO THE EAST-
NORTHEAST WILL BUILD. RELIABLE MODEL INTENSITY GUIDANCE IS IN 
UNANIMOUS AGREEMENT WITH A PEAK IN INTENSITY AT TAU 12 FOLLOWED BY A 
STEADY WEAKENING TREND THROUGH THE FORECAST PERIOD.

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