WDIO31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 01B (ONE) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.1N 83.6E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 743 NM SOUTH-SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN AREA
OF DEEP CONVECTION INTENSIFYING OVER AN ASSESSED LOW LEVEL
CIRCULATION CENTER (LLCC). A PARTIAL 041602Z ASCAT-B PASS REVEALS
35 KTS IN THE NORTHERN AND EASTERN PERIPHERIES. ENVIRONMENTAL
ANALYSIS INDICATES TC 01B IS IN AN AREA MARGINAL FOR FURTHER
DEVELOPMENT WITH GOOD POLEWARD OUTFLOW ALOFT AND WARM (27-28C) SEA
SURFACE TEMPERATURES, OFFSET BY MODERATE (15-20 KTS) VERTICAL WIND
SHEAR (VWS). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON THE AFOREMENTIONED ASCAT PASS AS WELL AS THE PGTW FIX. THE
INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED
ON THE AFOREMENTIONED ASCAT PASS AND PGTW DVORAK ESTIMATE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 01B IS IN A RELATIVELY QUASI-STATIONARY
STATE AND WILL SLIGHTLY INTENSIFY TO 40 KTS BY TAU 12. THE OVERALL
FORECASTED TRACK TAKES TC 01B TO THE NORTHWEST BEFORE TURNING
SOUTHWEST AFTER TAU 12 DUE TO THE STR BUILDING IN FROM THE
EAST-NORTHEAST. BY TAU 24, TC 01B WILL BE ON A SOUTHWESTERLY TRACK
AND MAINTAIN 40 KTS INTENSITY. BY 36, DRY AIR FROM THE WEST WILL
BEGIN TO WRAP INTO THE SOUTHERN PERIPHERY AND VWS WILL BECOME
UNFAVORABLE, DECREASING INTENSITY TO 35 KTS AND ULTIMATELY
BEGINNING THE DISSIPATION PHASE OF THE SYSTEM. BY TAU 48, TC 01B
WILL BEGIN LAND INTERACTION WITH SOUTHEAST INDIA AND SRI LANKA TO
THE SOUTHWEST AS DRY AIR WILL BE COMPLETELY ENTRAINED IN THE
CENTER OF THE CIRCULATION, DECREASING THE INTENSITY TO 30 KTS.
FULL DISSIPATION IS EXPECTED BY TAU 72, AS THE CENTER ON
CIRCULATION WILL PASS SOUTH OF KODIYAKARAI, INDIA.

MODEL DISCUSSION: MODEL TRACK GUIDANCE AGREES TC 01B WILL MOVE
NORTHWESTWARD OVER THE FIRST 12 HOURS AND THEN MAKE ITS TURN
SOUTHWEST THEREAFTER. HOWEVER, THERE IS A TRACK SPREAD OF 40-50 NM
AMONG CONSENSUS MEMBERS, WITH NAVGEM BEING THE OUTLIER WITH AN
AGGRESSIVE SOUTH-SOUTHWESTWARD TRACK. THE JTWC FORECAST TRACK IS
PLACED WITH MEDIUM CONFIDENCE AND SLIGHTLY RIGHT OF CONSENSUS TO
OFFSET NAVGEM. FORECAST INTENSITY GUIDANCE IS IN GOOD AGREEMENT
INDICATING A NOMINAL INCREASE THROUGH TAU 24, FOLLOWED BY A SHARP
DECREASE THEREAFTER AND THROUGHOUT THE REMAINDER OF THE FORECAST
PERIOD.

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