WDPN31 PGTW 200900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (ONE) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.0N 157.1E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 142 NM NORTH-NORTHWEST OF POHNPEI
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
FRAGMENTED CELLS OF CONVECTION COMPRISING THE VARIOUS BANDING
FEATURES FULLY OBSCURING THE LOW LEVEL CIRCULATION CENTER. A
200544Z SSMIS 89GHZ COLOR COMPOSITE MICROWAVE IMAGE DEPICTS
SLIGHTLY IMPROVED CONVECTIVE STRUCTURES AS THE PRIMARY DEEP
CONVECTION IS NOTICEABLY CURLING INTO THE CIRCULATION AND FORMING A
HOOK-LIKE APPEARANCE. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON EIR AND SSMIS IMAGERY.  THE INITIAL INTENSITY
OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
PREPONDERANCE OF INTENSITY GUIDANCE INDICATING 35KTS. ADT IS A
NOTABLE OUTLIER AT T3.0, BUT UPON FURTHER INVESTIGATION, ADT USED A
.67 ARC WHILE JTWC LIBERALLY ANALYZED A .25 WRAP ON THE LOG10
SPIRAL WHICH ACCOUNTS FOR THE DISCREPANCY WHILE CASTING DOUBT ON
THE VERACITY OF THEIR INTENSITY ESTIMATE.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NEAR-EQUITORIAL RIDGE (NER) TO THE
EAST-NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 45 KTS AT 200530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL

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: TS 01W IS FORECAST TO CONTINUE ITS GRADUAL
WESTWARD COURSE CHANGE AS THE NER TO THE EAST IS GRADUALLY REPLACED
AS THE STEERING FEATURE BY A FORMING SUB-TROPICAL RIDGE (STR) TO
THE NORTH. WHILE STILL IN A MARGINALLY FAVORABLE ENVIRONMENT
CHARACTERIZED BY HIGH SST AND RADIAL OUTFLOW ALOFT, PARTIALLY
OFFSET BY BUILDING MID-LEVEL VERTICAL WIND SHEAR (VWS), 01W IS
FORECAST TO SLIGHTLY INTENSIFY OVER THE NEXT 12 HOURS. BY TAU 24,
VWS WILL CONTINUE TO INCREASE AS THE BUILDING STR TO THE NORTH
BEGINS TO ENTRAIN DRY AIR INTO THE SYSTEM RESULTING IN STEADY
WEAKENING. AFTER TAU 24, 01W WILL CONTINUE TO WEAKEN AS IT TRACKS
GENERALLY WEST-NORTHWESTWARD, EVENTUALLY DISSIPATING BY TAU 96.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIR AGREEMENT THAT 01W
WILL CONTINUE ITS GRADUAL WESTWARD TURN THROUGH THE FORECAST
PERIOD. NVGM, GFS AND AEMI ARE GROUPED POLEWARD OF THE MULTI-MODEL
CONSENSUS WHILE COAMPS-TC, HWRF AND ECMWF ARE EQUATORWARD OF THE
CONSENSUS AS VARIOUS MEMBERS RESOLVE THE BUILDING STR TO THE NORTH.
FOR THESE REASONS THE JTWC FORECAST TRACK IS PLACED CLOSE TO THE
MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE. RELIABLE MODEL
INTENSITY GUIDANCE IS IN FAIR AGREEMENT WITH DECAY-SHIPS AND HWRF
INDICATING CONTINUED INTENSIFICATION THOUGH TAU 12 WHILE THE
REMAINING MEMBERS SHOW NEGLIGIBLE WEAKENING THROUGH TAU 24, AFTER
WHICH ALL MEMBERS EXCEPT DECAY-SHIPS SHOW WEAKENING THROUGH THE
FORECAST PERIOD. FOR THESE REASONS THE JTWC INTENSITY FORECAST IS
PLACED WITH MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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