WDPN31 PGTW 250300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.9N 143.4E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 211 NM NORTH-NORTHWEST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 12W WITH AN INCREASINGLY DEFINED, PARTIALLY EXPOSED
LOW-LEVEL CIRCULATION CENTER (LLCC). THE CONVECTIVE BANDING THAT
WAS PRESENT 6 HOURS AGO HAS SINCE BEEN SHEARED OFF TO THE SOUTH,
BUT DEEP CONVECTION REMAINS PERSISTENT IN THE SOUTHERN SEMICIRCLE.
A 242040 SSMIS 91 GHZ MICROWAVE IMAGE CAPTURED THE CURVED BAND OF
CONVECTION TO THE SOUTH AND THE LOW-LEVEL CLOUDS TIGHTLY WRAPPING
INTO THE ASSESSED CENTER. ENVIRONMENTAL ANALYSIS INDICATES THAT 12W
IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE
EQUATORWARD OUTFLOW ALOFT, HIGH (30-35 KTS NORTHERLY VERTICAL WIND
SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL
POSITION, INTENSITY, AND WIND RADII ARE ALL PLACED WITH HIGH
CONFIDENCE BASED ON A TIMELY 242320Z METOP-B ASCAT PASS SHOWING A
SWATH OF 35-40 KTS WITHIN THE SOUTHERN AND SOUTHEASTERN
PERIPHERIES. AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES ARE
SLIGHTLY LOWER, LIKELY DUE TO THE LACK OF CENTRAL CONVECTION IN
RESPONSE TO THE ELEVATED NORTHERLY SHEAR ACTING ON THE SYSTEM.

INITIAL WIND RADII BASIS: 242320Z METOP-B ASCAT SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WEAK RIDGING TO THE EAST WHICH IS
DRIVING THE SYSTEM NORTHWARD

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 33 KTS AT 250000Z
   CIMSS AIDT: 37 KTS AT 250000Z
   CIMSS DPRINT: 28 KTS AT 250040Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 30-35 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 12W IS FORECAST TO GENERALLY
NORTH-NORTHEASTWARD, ALONG THE WESTERN PERIPHERY OF A BUILDING
SUBTROPICAL RIDGE TO THE EAST THROUGH TAU 72. AFTER TAU 72, TRACK
SPEEDS ARE EXPECTED TO SLOW AS THE INFLUENCE FROM THE SUBTROPICAL
RIDGE WEAKENS. AROUND TAU 96, A BELT OF ENHANCED SOUTHWESTERLY
WINDS WILL BEGIN INTERACTING WITH THE VORTEX AND WILL PULL THE
VORTEX NORTHEASTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD.
THERE IS SOME UNCERTAINTY REGARDING THE EXACT TIMING OF THE
NORTHEASTWARD TURN, AS IT DEPENDS ON THE ONSET OF THE ENHANCED
SOUTHWESTERLY FLOW. THE SYSTEM COULD POTENTIALLY DRIFT
NORTHWESTWARD BEFORE MAKING THE NORTHEASTWARD TURN AS A SUBTROPICAL
RIDGE BUILDS IN OVER SOUTHERN JAPAN AND INTERACTS WITH THE VORTEX.
ALL ECMWF AND GEFS ENSEMBLE MEMBERS DO KEEP THE SYSTEM FROM
TRACKING INTO HONSHU THOUGH. REGARDING INTENSITY, 12W IS FORECAST
TO INTENSIFY OVER THE NEXT 48 HOURS AS THE SYSTEM CONTINUES TO
CONSOLIDATE. NORTHERLY VERTICAL WIND SHEAR IS EXPECTED TO REMAIN
NEAR 30 KTS, HOWEVER, INTERACTION WITH AN
UPPER-LEVEL SHORTWAVE TROUGH WILL DRASTICALLY ENHANCE THE EASTWARD
OUTFLOW THROUGH TAU 72. CURRENTLY, A PEAK INTENSITY OF 65 KTS IS
FORECAST TO OCCUR AT TAU 48 AND PERSIST THROUGH TAU 72. NEAR 
TAU 72, AN UPPER-LEVEL CYCLONE IS EXPECTED TO BE PLACED OVER THE 
VORTEX, WHICH WILL CAUSE INCREASED DRY AIR ENTRAINMENT AND 
SIGNIFICANTLY DECREASED OUTFLOW ALOFT. AS A RESULT, 12W IS FORECAST
TO STOP INTENSIFYING AND WEAKEN UNDER THE INFLUENCE OF THE
UPPER-LEVEL CYCLONE.   

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 72 WITH A 160 NM CROSS TRACK SPREAD AT TAU
72. AFTER TAU 72, MODELS BEGIN TO DIVERGE DUE TO SOME MODELS
TRACKING THE SYSTEM QUICKLY OFF TO THE NORTHEAST (GFS, GALWEM, AND
UKMET) WHILE OTHERS SLOW THE SYSTEM DOWN BEFORE TURNING
NORTHEASTWARD (ECMWF, JGSM AND THE ECMWF ENSEMBLE MEAN). THE JTWC
TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS THROUGH
TAU 72 AND THEN MORE IN LINE WITH THE LATTER SCENARIO THOUGH TAU
120. INTENSITY GUIDANCE AGREES ON INTENSIFICATION THROUGH TAU 48 TO
A PEAK RANGING FROM 55-75 KTS. AFTER TAU 48, MODELS HALT THE
INTENSIFICATION TREND AND MARGINALLY WEAKEN THE SYSTEM THROUGH THE
REMAINDER OF THE FORECAST PERIOD. COAMPS-TC (GFS BASED) CONTINUES
TO BE THE MOST AGGRESSIVE MODEL WITH A PEAK INTENSITY OF 75 KTS AT
TAU 48. OVERALL, THE JTWC INTENSITY FORECAST IS PLACED IN LINE WITH
THE CONSENSUS WITH MEDIUM CONFIDENCE.

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