
rainbands affecting the southern japanese islands...
WDPN31 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (TORAJI) WARNING NR
05//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 15W (TORAJI), LOCATED APPROXIMATELY 100 NM
NORTHWEST OF KADENA AB, HAS TRACKED NORTHEASTWARD AT 05 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS A CONSOLIDATED LOW-LEVEL CIRCULATION CENTER (LLCC)
ASSOCIATED WITH SEVERAL CONVECTIVE BANDING FEATURES WRAPPING INTO
THE LLCC. A 021232Z METOP-A MICROWAVE IMAGE REVEALS A SYSTEM WITH A
PREDOMINANTLY SHALLOW TO MID-LEVEL CONVECTIVE SIGNATURE AS WELL AS A
STRONG BANDING FEATURE WRAPPING ACROSS THE EASTERN SEMI-CIRCLE.
RADAR IMAGERY FROM OKINAWA, JAPAN, SHOWS A WELL SUSTAINED STRUCTURE
OVER THE LAST SIX HOURS AS CONVECTIVE BANDING CONTINUES TO TIGHTLY
WRAP INTO THE LLCC. THE INITIAL POSITION IS BASED ON THE EIR LOOP,
THE RADAR IMAGERY AND THE AFOREMENTIONED MICROWAVE IMAGE WITH GOOD
CONFIDENCE. THE INITIAL INTENSITY HAS BEEN MAINTAINED AT 35 KNOTS
BASED ON THE DVORAK INTENSITY ESTIMATES OF THE SAME VALUE FROM PGTW
AND RJTD. UPPER-LEVEL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT
CHARACTERIZED BY LOW TO MODERATE (10 TO 20 KNOTS) VERTICAL WIND
SHEAR (VWS) AND GOOD EQUATORWARD AND POLEWARD OUTFLOW. TS 15W IS
CURRENTLY TRACKING ALONG THE SOUTHERN PERIPHERY OF THE PASSING DEEP
MID-LATITUDE TROUGH NORTHWEST OF THE SYSTEM.
3. FORECAST REASONING.
A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC
REASONING MESSAGE.
B. TS 15W IS EXPECTED TO CONTINUE TRACKING TO THE NORTHEAST UNDER
THE INFLUENCE OF THE PASSING DEEP MID-LATITUDE TROUGH OVER THE NEXT
24 HOURS. BETWEEN TAU 24 AND TAU 72 THE SYSTEM IS EXPECTED TO ENTER
AN AREA OF WEAK ENVIRONMENTAL STEERING AND TRACK SPEEDS WILL SLOW AS
THE TROUGH PASSES AND A SUBTROPICAL RIDGE (STR) BEGINS TO BUILD INTO
THE REGION ACROSS KYUSHU. AS THE RIDGE BUILDS, TS 15W WILL TURN
POLEWARD ALONG THE WESTERN PERIPHERY OF THE STR. THE INTENSITY OF TS
15W IS EXPECTED TO GRADUALLY INCREASE THROUGH TAU 36 TO A PEAK OF 45
KTS UNDER FAVORABLE UPPER-LEVEL CONDITIONS. AFTER TAU 36, INCREASING
VWS FROM THE PASSING TROUGH AND BUILDING RIDGE WILL BEGIN TO WEAKEN
THE SYSTEM. TORAJI IS FORECAST TO FIRST BEGIN INTERACTING WITH THE
BAROCLINIC ZONE AND MID-LATITUDE WESTERLIES AS IT IS DRIVEN POLEWARD
BY THE STR NEAR TAU 72. THIS INTERACTION WILL BEGIN THE
EXTRATROPICAL TRANSITION PROCESS.
C. IN THE EXTENDED TAUS, THE SYSTEM WILL BEGIN TO TRACK MORE
NORTHEASTWARD TOWARDS THE SEA OF JAPAN ONCE TORAJI CROSSES THE RIDGE
AXIS. EXTRATROPICAL TRANSITION IS EXPECTED TO BE COMPLETED BY TAU 96
AS THE SYSTEM WILL BE FULLY EMBEDDED IN THE BAROCLINIC ZONE. DYNAMIC
MODEL GUIDANCE IS IN FAIRLY TIGHT AGREEMENT WITH THE NORTHEAST TRACK
THROUGH TAU 24, ALTHOUGH AT VARYING TRACK SPEEDS. AFTER THE DEEP MID-
LATITUDE TROUGH PASSES, THERE IS SIGNIFICANT UNCERTAINTY IN THE
FORECAST TRACK AS MANY OF THE CONSENSUS MEMBERS BEGIN TO MEANDER
ABOUT DUE TO THE LACK OF A DOMINANT STEERING MECHANISM IN THE AREA.
THE NUMERICAL MODELS SHOW DIFFERING SOLUTIONS TO THE TIMING AND
STRENGTH OF THE STR THAT IS EXPECTED TO BUILD IN AFTER THE PASSAGE
OF THE TROUGH. NAVGEM, ECMWF, AND THE JAPANESE ENSEMBLE INDICATE A
STRONG STR, WHICH SIGNIFICANTLY WEAKENS THE SYSTEM AND DRIVES THE
WEAKENED VORTEX NORTHWEST IN THE EXTENDED TAUS. GFS, HWRF, AND THE
GFS ENSEMBLE, HOWEVER, CONTINUE TO QUICKLY ACCELERATE THE SYSTEM TO
THE NORTHEAST AHEAD THE TROUGH AND DO NOT BUILD THE RIDGE IN THE
EXTENDED TAUS. THE JTWC FORECAST TRACK IS LAID CLOSE TO THE MULTI-
MODEL CONSENSUS WITH OVERALL LOW CONFIDENCE DUE TO THE UNCERTAINTY
ASSOCIATED WITH THE WEAK STEERING MECHANISM AND THE REBUILDING STR
IN THE MODELS.//
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