WDIO32 PGTW 290300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 05B (DITWAH) WARNING 
NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.4N 80.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 905 NM SOUTH-SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
SHALLOW, RAGGED, AND POORLY DEFINED LOW-LEVEL CIRCULATION WITH
PATCHY DEEP CONVECTION CONFINED TO THE NORTHERN AND WESTERN
QUADRANTS AND DISPLACED FROM THE CENTER. THOUGH TROPICAL CYCLONE
(TC) 05B IS NOW BACK OVER WATER, THE ENVIRONMENT REMAINS MARGINAL,
AS DRY AIR CONTINUES TO ERODE 05B WHILE SOUTHERLY VERTICAL WIND
SHEAR HAS STRENGTHENED TO 15-20 KTS. THE SURFACE STATION FROM
MANNAR ISLAND, SRI LANKA IS REPORTING 14 KTS FROM THE
WEST-NORTHWEST, INDICATING 05B HAS MOVED NORTHWARD. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE EXPOSED
RAGGED LLCC. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE T2.5 DVORAK FIX FROM PGTW AND THE 34
KTS ESTIMATED BY CIMSS DPRINT LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: THE WESTERN EXTENSION OF THE
SUBTROPICAL RIDGE (STR) CENTERED OVER SOUTHEAST ASIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   CIMSS D-PRINT: 34 KTS AT 280000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 05B (DITWAH) WILL CONTINUE ON A GENERALLY
NORTHWARD TRACK FOR THE DURATION OF THE FORECAST PERIOD. BY TAU 12,
THE SOUTHERLY VERTICAL WIND SHEAR IS EXPECTED TO INCREASE TO 20-25
KTS, AIDING THE DRY AIR ENTRAINMENT AND CONTRIBUTING TO
DISSIPATION. 05B IS FORECAST TO TEETER AROUND TROPICAL STORM
STRENGTH BEFORE FINALLY SUCCUMBING TO THE DRY AIR AND VERTICAL WIND
SHEAR NO LATER THAN TAU 36.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG
AGREEMENT, EXCLUDING NAVGEM, THAT 05B WILL TRACK NORTHWARD FOR THE
DURATION OF THE FORECAST PERIOD. NAVGEM IS THE SOLE OUTLIER,
MAINTAINING THAT 05B WILL ASSUME A NORTH-NORTHEASTWARD TRACK. THE
JTWC TRACK FORECAST LIES IN AGREEMENT WITH THE MULTI-MODEL
CONSENSUS AND THE BULK OF INDIVIDUAL MEMBERS WITH HIGH CONFIDENCE.
THE INTENSITY GUIDANCE IS SPLIT, WITH HWRF, HAFS, AND GFS WEAKENING
05B BELOW 35 KTS BY TAU 36. COAMPS-TC, BOTH GFS BASED AND NAVGEM
BASED, INTENSIFY 05B TO 40-50 KTS AT TAU 36. BASED ON THE
INCREASING VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT, THE JTWC
INTENSITY FORECAST LIES CLOSER TO HWRF, HAFS, AND GFS WITH MEDIUM
CONFIDENCE. THERE IS UNCERTAINTY IN FUTURE TAUS, DUE TO ALL MODELS
BRIEFLY REINTENSIFYING 05B TO 35 KTS AT TAU 48, INDICATING THE
POSSIBILITY THAT 05B COULD SURVIVE PAST TAU 36.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM//
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