WDPN31 PGTW 150300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W WARNING NR 02//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
A. TS 12W HAS INTENSIFIED RAPIDLY OVER THE PAST 12 HOURS
WHILE TRACKING GENERALLY NORTH-NORTHEASTWARD TO NORTHWARD
ALONG THE WESTERN PERIPHERY OF THE LOW TO MID-LEVEL SUB-
TROPICAL STEERING RIDGE. A LARGE AND SYMMETRIC CENTRAL DENSE 
OVERCAST (CDO) FEATURE DEVELOPED OVER AN INCREASINGLY BETTER 
DEFINED LOW LEVEL CIRCULATION CENTER (LLCC), AS EVIDENT 
IN SEQUENTIAL QUIKSCAT PASSES AND RECENT MICROWAVE IMAGERY. 
LIMITED AND WEAK CONVECTIVE BANDING HAS SINCE GIVEN WAY TO 
MORE TIGHTLY CURVED BANDING. 
B. THE INITIAL INTENSITY OF TS 12W IS BASED ON DVORAK ANALYSES 
FROM PGTW AND KNES RANGING FROM 30 TO 45 KNOTS. HOWEVER, DUE
TO THE RAPID INTENSIFICATION OVER THE PAST 12 HOURS, THESE
NUMBERS ARE ARTIFICIALLY LOWER DUE TO FIXING CONSTRAINTS. THUS,
THE INITIAL INTENSITY REFLECTS THE HIGHER END OF THIS RANGE OF
INTENSITIES. THE SYSTEM CONTINUES TO TRACK GENERALLY NORTHWARD 
ALONG THE WESTERN PERIPHERY OF THE LOW TO MID-LEVEL SUBTROPICAL 
STEERING RIDGE, IN WATERS GREATER THAN 26 DEGREES CELSIUS, AND 
UNDER FAVORABLE CONDITIONS ALOFT. A 200MB ANTICYCLONE IS PRO-
VIDING RADIAL OUTFLOW FOR THE SYSTEM, ALL THE WHILE SHIELDING 
THE SYSTEM FROM VERTICAL WIND SHEAR.
3. FORECAST REASONING.
A. THE FORECAST HAS BEEN SHIFTED POLEWARD FROM THE INITIAL 
FORECAST AS A DIRECT CONSEQUENCE OF THE PREVIOUS 12 HOUR MOTION 
OF THE SYSTEM. INTENSITIES HAVE ALSO BEEN ADJUSTED TO REFLECT 
A HIGHER THAN ANTICIPATED INITIAL INTENSITY.
B. THE SYSTEM WILL TRACK PROGRESSIVELY MORE EASTWARD THROUGH EACH
FORECAST TAUS IN RESPONSE TO IMMINENT INTERACTION WITH THE MID-
LATITUDE WESTERLIES TO THE NORTH NEAR TAU 24. PRIOR TO TAU 24 
THE SYSTEM SHOULD INTENSIFY MORE MODESTLY IN A LOW VERTICAL
WIND SHEAR ENVIRONMENT, COMBINED WITH CONTINUED RADIAL OUTFLOW.
THIS OUTFLOW WILL BE ENHANCED PRIOR TO COMPLETE INTERACTION
WITH THE WESTERLY JET, BUT HEIGHTENED VERTICAL WIND SHEAR WILL 
HOLD INTENSITIES STEADY. SEA SURFACE TEMPERATURES WILL ALSO 
REMAIN FAVORABLE THROUGHOUT THE SHORT INTENSIFICATION PERIOD. THE 
SYSTEM IS FORECAST TO FULLY DISSIPATE DUE TO VERTICAL WIND SHEAR; 
HOWEVER, ONCE AGAIN DUE TO THE STRONGER SIGNATURE OF THE SYSTEM, 
THE SYSTEM MAY NOT WEAKEN BELOW 25 KNOTS PRIOR TO INTERACTION 
WITH THE BAROCLINIC ZONE. THUS, A PERIOD OF EXTRATROPICAL TRAN-
SITION MAY OCCUR AS THE SYSTEM WEAKENS. BEYOND TAU 24 THE SYSTEM
SHOULD BE FULLY ENVELOPED IN THE WESTERLIES (AS INDICATED BY
150000Z SKEW-T ANALYSES FROM EASTERN JAPAN) AND WILL ACCELERATE 
OFF TO THE EAST-NORTHEAST AS A DISSIPATED SYSTEM. 
FORECAST TEAM: BRAVO//
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