WDIO31 PGTW 050900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 01B (ONE) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.6N 83.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 708 NM SOUTH-SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) ON THE SOUTHWEST SIDE
OF AN AREA OF CYCLONICALLY CURVED CONVECTION SHEARED OFF TO THE
NORTHEAST. A 050028Z SSMIS 91GHZ MICROWAVE IMAGE SHOWED FRAGMENTARY
AND DISORGANIZED CONVECTION LIMITED TO THE NORTHERN HEMISPHERE OF
THE CIRCULATION. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE EXPOSED LLCC. THE INITIAL INTENSITY IS
ASSESSED AT A GENEROUS 35 KNOTS WITH MEDIUM CONFIDENCE, IN LINE
WITH THE PGTW AND ADT DVORAK CURRENT INTENSITY ESTIMATES, THOUGH
FINAL-T NUMBERS WERE ONLY T1.5. PARTIAL ASCAT PASSES AT BOTH
050349Z AND 050436Z, WHILST ONLY COVERING THE WESTERN PORTION OF
THE CIRCULATION, INDICATED WINDS OF 30 KNOTS OR LESS IN THESE
SECTORS, THOUGH IT IS LIKELY THAT 35 KNOTS WINDS ARE PRESENT IN THE
NORTHEASTERN SECTOR, WHICH THE SCATTEROMETERS DID NOT SAMPLE. THE
OVERALL ENVIRONMENT IS MARGINAL, WITH WARM SSTS AND MODERATE
POLEWARD OUTFLOW. AS EVIDENCED IN ANIMATED WATER VAPOR IMAGERY, DRY
AIR IS MOVING IN FROM THE WEST AND SOUTH, INHIBITING CONVECTIVE
DEVELOPMENT ACROSS THE ENTIRETY OF THE SOUTHERN HEMISPHERE OF THE
CIRCULATION. FINALLY, WHILE CIMSS ANALYSIS REVEALS LOW VWS, HWRF
AREA AVERAGED SKEW-T ANALYSIS REVEALS MODERATE TO STRONG (15-20
KNOTS) MID-LEVEL SOUTHWESTERLY SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A LOW TO MID-LEVEL
SUBTROPICAL RIDGE CENTERED OVER THE SOUTH CHINA SEA.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   DEMS: T2.0 - 30 KTS
   CIMSS ADT: 37 KTS AT 050615Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENCROACHING IN FROM THE WEST. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING. HOWEVER, THE FORECAST
PERIOD HAS BEEN TRUNCATED TO 24 HOURS. 

FORECAST DISCUSSION: TC 01B HAS BEEN MOVING SLOWLY NORTHWARD OVER
THE PREVIOUS 12 HOURS OR SO, ALONG THE MID-LEVEL STEERING RIDGE
CENTERED WELL TO THE EAST. HOWEVER, AS THE SYSTEM CONTINUES TO
WEAKEN THE STEERING LEVEL WILL LOWER, AND THE EASTERLY FLOW ALONG
THE SOUTHERN PERIPHERY OF THE ANTICYCLONE OVER NORTH-CENTRAL INDIA
WILL ASSUME THE DOMINATE STEERING ROLE. ONCE THIS OCCURS, EXPECTED
WITHIN THE NEXT 12 HOURS, THE SYSTEM WILL TURN SHARPLY TO THE WEST.
AS DEPICTED IN THE HWRF AREA AVERAGED SKEW-T DATA, MID-LEVEL
SOUTHWESTERLY SHEAR IS FAIRLY STRONG, AND IS PUSHING THE CONVECTION
FAR TO THE NORTHEAST OFF THE LOW LEVEL CENTER. TC 01B WILL STRUGGLE
IN THE FACE OF THE DRY AIR ENTRAINMENT AND MID-LEVEL SHEAR AND IS
EXPECTED TO STEADILY WEAKEN OVER THE PERIOD OF THE FORECAST,
DISSIPATING BY TAU 24 AS IT IS COMPLETELY ENGULFED IN THE DRY AIR
EMANATING FROM THE INDIAN SUBCONTINENT. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT, WITH ALL
CONSENSUS MEMBERS IN CONCURRENCE ON THE SHARP TURN TO THE WEST
WITHIN THE NEXT 12 HOURS. THE JTWC TRACK LIES ON THE NORTHERN EDGE
OF THE ENVELOPE TO ACCOUNT FOR THE NEAR TERM NORTHERLY MOTION, WITH
HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN VERY GOOD AGREEMENT, WITH
THE BULK OF THE MEMBERS SUPPORTING DISSIPATION BETWEEN TAU 24 AND
TAU 30, THOUGH THE COAMPS-TC MODEL SUGGESTS THE SYSTEM HOLDS ON
ANOTHER 12 HOURS. THE JTWC FORECAST CLOSELY TRACKS THE CONSENSUS
MEAN WITH HIGH CONFIDENCE.  

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