WDPN32 PGTW 310300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (TWENTYSEVEN) WARNING 
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 7.8N 134.1E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 35 NM NORTH-NORTHWEST OF KOROR
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM 27W IS LIKE THE LITTLE ENGINE THAT COULD, STUBBORNLY
INTENSIFYING IN THE FACE OF STRONG AND PERSISTENT NORTHEASTERLY
FLOW ALOFT. AN IMPRESSIVE CENTRAL DENSE OVERCAST OF DEEP CONVECTION
HAS DEVELOPED OVER THE PAST SIX HOURS, WITH CLOUD TOP TEMPS AS COLD
AS -95C AND LARGE, PERSISTENT BURSTS OF LIGHTNING IN THE VICINITY
OF KOROR. SURFACE OBSERVATIONS FROM KOROR HAVE DESCRIBED FREQUENT
LIGHTNING, THUNDERSTORMS, AND HEAVY RAIN, WITH PRESSURES FALLING TO
AS LOW AS 1001MB AS THE CENTER OF TS 27W PASSED. WINDS ARE NOW OUT
OF THE SOUTH AND PRESSURES ARE RISING, INDICATING THE CENTER IS NOW TO
THE WEST OF THE ISLANDS. WHILE THE LOW LEVEL CIRCULATION CENTER IS
OBSCURED UNDER THE CDO, A PARTIAL 310007Z ASCAT-B SCATTEROMETER
PASS PROVIDED MUCH NEEDED CLARITY TO THE INITIAL POSITION. THE
INITIAL INTENSITY IS INCREASED TO 35 KNOTS BASED ON THE
SCATTEROMETER DATA, WITH NON-QC FLAGGED WINDS OF 35 KNOTS EVIDENT
TO THE SOUTH AND SOUTHWEST OF THE CENTER, WHICH ALIGNS WITH THE ADT
AND THE MID-POINT OF THE AGENCY FIXES. THE OVERALL ENVIRONMENT IS
MARGINAL, WITH WARM SSTS AND STRONG EQUATORWARD OUTFLOW BEING
OFFSET BY STRONG NORTHEASTERLY FLOW ALOFT. HOWEVER, THE 310000Z
KOROR SOUNDING SHOWS DIVERGENT FLOW AT THE 200MB LEVEL, WITH WINDS
OUT OF THE SOUTHWEST AT JUST 10-20 KNOTS. THE YAP SOUNDING ALSO
SHOWED LIGHTER 200MB WINDS THAN THE GFS WOULD SUGGEST, MORE IN LINE
WITH THE ECMWF FIELDS. FINALLY THE CIMSS ANALYSIS SHOWS STRONG
DIVERGENT FLOW OVER TOP OF THE SYSTEM, LIKELY IN RESPONSE TO THE
SURGING CONVECTION PUSHING BACK ON THE ENVIRONMENTAL FLOW. BOTTOM
LINE, THE SYSTEM HAS COCOONED ITSELF IN A MESOSCALE POUCH OF LOWER
SHEAR, ALLOWING FOR THE RECENT INTENSIFICATION.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 32 KTS AT 302340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM 27W, HAVING SLID WEST-SOUTHWEST
OVER THE PAST SIX HOURS, IS STILL EXPECTED TO MAKE A GRADUAL TURN
TO THE WEST OVER THE NEXT 12 HOURS. THEN, AS THE STEERING RIDGE
SLIDES A BIT TO THE EAST AND THE WESTERN PERIPHERY OF IT ORIENTS TO
A MORE NORTHWEST-SOUTHEAST DIRECTION, TS 27W WILL TURN ONTO A MORE
NORTHWESTWARD TRACK THROUGH THE END OF THE FORECAST PERIOD. THE
IMPRESSIVE BURST OF CONVECTIVE ACTIVITY HAS CREATED A NICE COCOON
OF RELATIVELY LESS SHEAR IN WHICH TS 27W HAS BEEN ABLE TO INTENSIFY
OVER THE PAST SIX HOURS. THE ECMWF MODEL SUGGESTS THE SYSTEM WILL
BE ABLE TO SUSTAIN THIS SETUP FOR ANOTHER 12 HOURS OR SO, AND BASED
ON THE FACT THAT LATEST SOUNDINGS SEEM TO SHOW THAT THE ECMWF IS
CAPTURING THE ENVIRONMENT THE BEST, THE FORECAST CALLS FOR THE
SYSTEM TO MAINTAIN MINIMAL TS STRENGTH FOR THE FIRST 12 HOURS OF
THE FORECAST. THEN, MID-LEVEL DRY AIR AND UPPER-LEVEL CONVERGENCE
CURRENTLY SEEN IN THE YAP SOUNDINGS, WILL PUSH SOUTH OVER THE
SYSTEM, AND THIS WILL SERVE TO SLOWLY WEAKEN THE SYSTEM AFTER TAU
24. THE SYSTEM IS EXPECTED TO ULTIMATELY DISSIPATE AS A TROPICAL
CYCLONE NO LATER THAN TAU 48, TO THE EAST OF MINDANAO.  

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT, WITH ALL
CONSENSUS MEMBERS SAVE FOR NAVGEM, CONTAINED IN A TIGHT ENVELOPE
WITH MINIMAL SPREAD, LENDING HIGH CONFIDENCE TO THE JTWC FORECAST
TRACK. INTENSITY GUIDANCE REMAINS MIXED, WITH THE DECAY-SHIPS (BOTH
GFS AND NAVGEM) INTENSIFYING THE SYSTEM UNREALISTICALLY TO A PEAK
OVER 55 KNOTS. MEANWHILE, THE MESOSCALE MODELS INCLUDING HWRF AND
THE MESOSCALE GFS, INDICATE A FLAT INTENSITY TREND THROUGH ABOUT
TAU 12 FOLLOWED BY STEADY WEAKENING TO THE END OF THE FORECAST. THE
JTWC FORECAST FOLLOWS THE MESOSCALE GUIDANCE WITH MEDIUM
CONFIDENCE. 

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