WDPN31 PGTW 120300
MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W WARNING NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. OVER THE PAST 12 HOURS, THE SYSTEM HAS QUICKLY CONSOLIDATED
INTO A TROPICAL STORM (TS) AND SLOWED TO APPROXIMATELY 10 KNOTS SOA.
ANIMATED MULTISPECTRAL IMAGERY DEPICTS A LARGE CDO FEATURE WITH THE
LOW-LEVEL CIRCULATION CENTER POSITIONED UNDER THE NORTHWESTERN EDGE
OF THE CDO. IMAGERY ALSO SHOWS IMPROVED INFLOW ALONG THE SOUTHERN
FLANK. ANIMATED WATER IMAGERY SHOWS FAIR BUT IMPROVED OUTFLOW WITH
A WEAK POLEWARD CHANNEL DEVELOPING AND IMPROVED EQUATORWARD OUT-
FLOW. AN 112352Z AMSU IMAGE SHOWED INTENSE DEEP CONVECTION PRIMARILY
OVER THE EASTERN SEMI-CIRCLE. AN 112033Z QUIKSCAT IMAGE AND THE
GUAM VAD WIND PROFILE DATA SHOW THAT THE SYSTEM HAS MODIFIED THE
SURROUNDING WINDFLOW, WHICH IS NOW FEEDING INTO THE STORM RATHER
THAN HINDERING DEVELOPMENT. 
   B. THE CURRENT POSITION IS BASED ON FIXES FROM PGTW AND KNES
DERIVED FROM RECENT ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND
MICROWAVE IMAGES. THE INTENSITY ESTIMATE OF 35 KNOTS IS BASED ON
THE LOWER RANGE OF DVORAK ESTIMATES OF 35 TO 45 KNOTS SUPPORTED
BY 25-30 KNOT UNFLAGGED WINDS ON THE LATEST QUIKSCAT IMAGE PLUS
SOME FLAGGED 35 KNOT WINDS. OVERALL, THE SYSTEM IS SITUATED WITHIN
A FAVORABLE ENVIRONMENT WITH WEAK VERTICAL WIND SHEAR (VWS), FAIR
OUTFLOW, HIGH SST AND OCEAN HEAT CONTENT. ADDITIONALLY, THE TOTAL
PRECIPITABLE WATER PRODUCT INDICATES AN EXPANDING MOISTURE ENVELOPE
SURROUNDING THE SYSTEM, WHICH WILL ALLOW THE SYSTEM TO DEVELOP
FURTHER.
3. FORECAST REASONING.
   A. THERE HAS BEEN A SIGNIFICANT SHIFT IN FORECAST PHILOSOPHY WITH
FORECAST INTENSITIES INCREASED UP TO 55 KNOTS AND THE EXTENDED FORE-
CAST TRACK INDICATING A MORE WEST-NORTHWESTWARD TRACK TOWARD CENTRAL
LUZON, PHILIPPINES.  
   B. TS 27W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF THE LOW- 
TO MID-LEVEL SUBTROPICAL RIDGE (STR) TO THE NORTH AND IS FORECAST TO
CONTINUE TRACKING GENERALLY WESTWARD THROUGH TAU 72. THE AVAILABLE
MODEL GUIDANCE IS LIMITED TO UK MET OFFICE, ECMWF, AND GFS. NEAR TAU
72, THE SYSTEM WILL BEGIN TO TRACK WEST-NORTHWESTWARD TOWARD A WEAK-
NESS IN THE STR BUT IS ALSO EXPECTED TO ENCOUNTER STRENGTHENING
NORTHERLY WINDS, COOLER, DRIER AIR AND HIGH VWS WHICH WILL SERVE
TO WEAKEN THE SYSTEM. THERE IS A HIGH DEGREE OF UNCERTAINTY IN
THE PEAK INTENSITY WITH THE POSSIBILITY THAT THE SYSTEM MAY REACH
AND EXCEED TYPHOON STRENGTH BY TAU 60. THE AIDS ARE LIMITED AND
THE CURRENT TRACK IS BASED PRIMARILY ON THE UK MET AND ECMWF
SOLUTIONS.
   C. THE EXTENDED TRACK IS MORE UNCERTAIN AND WILL DEPEND ON THE
PEAK INTENSITY AND THE STRENGTH OF THE NORTHEASTERLY SURGE. THE
CURRENT FORECAST SHOWS A WEST-NORTHWESTWARD TRACK AND WEAKENING
TREND DUE TO INCREASING VWS ASSOCIATED WITH THE NORTHERLY SURGE
AND INCREASING UPPER-LEVEL WESTERLY FLOW. THE SYSTEM IS EXPECTED
TO SLOW AS IT ENCOUNTERS THE HIGHER VWS. THERE IS A POSSIBILITY
REFLECTED IN SEVERAL MODELS THAT THE SYSTEM MAY TRACK MORE
NORTHWESTWARD PRIOR TO WEAKENING THEREFORE THERE IS HIGH
UNCERTAINTY IN THIS EXTENDED FORECAST.     
FORECAST TEAM: CHARLIE//
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