WDPN31 PGTW 231500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 02W (SURIGAE) WARNING 
NR 041//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 02W (SURIGAE), LOCATED APPROXIMATELY 223 NM SOUTH-
SOUTHEAST OF KADENA AB, HAS TRACKED EAST-NORTHEASTWARD AT 07 KNOTS 
OVER THE PAST SIX HOURS. THE CURRENT POSITION, INTENSITY AND WIND 
RADII ARE BASED ON A 231146Z METOP-A ASCAT PASS, WITH NEARLY FULL 
COVERAGE OF THE SYSTEM. TY 02W CONTINUES TO ROUND THE PERIPHERY OF 
DEEP-LAYER SUBTROPICAL RIDGING TO THE SOUTHEAST. OVER THE PAST SIX 
HOURS, TS 02W HAS TRANSITIONED TO A SUBTROPICAL STRUCTURE FEATURING 
A RAPIDLY EXPANDING WIND FIELD AND DISPLACEMENT OF REMAINING 
CONVECTION WELL TO THE EAST OF THE EXPOSED LOW-LEVEL CENTER. 
VERTICAL WIND SHEAR, DRIVEN BY THE FLOW ASSOCIATED WITH A SHORTWAVE 
TROUGH OVER THE SYSTEM, EXCEEDS 30 KNOTS, AND THE SYSTEM IS MOVING 
OVER AN AREA OF COOLER SEA SURFACE TEMPERATURES BELOW 26 DEGREES 
CELSIUS.
3. FORECAST REASONING.
   A. FORECAST WIND RADII SIZES HAVE INCREASED BASED ON RECENT 
EXPANSION AND MODEL GUIDANCE, AND EXTRATROPICAL TRANSITION IS NOW 
EXPECTED TO BE COMPLETE BY TAU 48. OTHERWISE, THERE IS NO 
SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TY 02W WILL CONTINUE TO WEAKEN IN THE NEAR-TERM AS VERTICAL 
WIND SHEAR PERSISTS AND THE SYSTEM PASSES OVER SLIGHTLY COOLER OCEAN 
WATER. HOWEVER, THE WEAKENING TREND WILL BE LIMITED AS INTERACTION 
WITH AFOREMENTIONED SHORTWAVE TROUGH OVER THE SYSTEM PROVIDES 
BAROCLINIC SUPPORT. TS 02W IS EXPECTED TO TURN EASTWARD AND SLIGHTLY 
EQUATORWARD OVER THE NEXT 36 HOURS FOLLOWING THE FLOW ASSOCIATED 
WITH REORIENTING SUBTROPICAL RIDGING TO THE SOUTH AND WEST, AND 
AHEAD OF AN AMPLIFYING, DEEP-LAYER MID-LATITUDE TROUGH DEVELOPING TO 
THE NORTH. AROUND OR JUST AFTER TAU 36, THIS AMPLIFYING TROUGH IS 
EXPECTED TO DIG FAR ENOUGH EQUATORWARD TO DIRECTLY INTERACT WITH TS 
02W. TRANSITION FROM A SUBTROPICAL TO EXTRATROPICAL STRUCTURE WILL 
OCCUR AS 02W MERGES WITH THIS TROUGH, WITH FULL TRANSITION 
ANTICIPATED BY TAU 48. FAVORABLE BAROCLINIC INTERACTION BETWEEN THE 
MID-LATITUDE TROUGH AND 02W WILL AID STRENGTHENING OF THE WIND FIELD 
AFTER TAU 36, RESULTING IN A REINTENSIFICATION TO STORM FORCE (50 
KNOTS) OR ABOVE. THE MAJORITY OF AVAILABLE NUMERICAL MODEL TRACK 
FORECAST GUIDANCE FAVORS ACCELERATION INTO THE MID-LATITUDE FLOW 
PATTERN FOLLOWING EXTRATROPICAL TRANSITION. THIS GUIDANCE IS IN VERY 
GOOD AGREEMENT THROUGH TAU 48, AND DIVERGES A BIT THEREAFTER DUE TO 
DIFFERING RATES OF ACCELERATION. THE JTWC TRACK FORECAST REMAINS 
NEAR THE MULTI-MODEL CONSENSUS, WITH HIGH CONFIDENCE OVERALL.//
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