WDPN32 PGTW 242100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (SAOLA) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.1N 123.9E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 328 NM SOUTH-SOUTHEAST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT LOW-LEVEL CIRCULATION WITH CURVED CONVECTIVE BANDING AROUND
ALL BUT THE NORTHWESTERN QUADRANT, WHICH REMAINS DEVOID OF
THUNDERSTORMS DUE TO ONGOING NORTHERLY SHEAR OF 15-20 KT.
CONVENTIONAL SATELLITE IMAGERY AND A 241926Z SSMIS MICROWAVE PASS
SUGGEST THAT THE VORTEX MAY BE TILTED SLIGHTLY SOUTHEASTWARD WITH
HEIGHT. THIS HAS PRECESSED CYCLONICALLY FROM THE MORE SOUTHWESTWARD
TILT OBSERVED 24 HOURS AGO, SUGGESTING THAT CONVECTION MAY BEGIN TO
PROPAGATE INTO THE UPSHEAR QUADRANTS IN THE NEAR FUTURE, GIVEN THAT
VERTICAL SHEAR IS ONLY MODERATE IN MAGNITUDE. COUNTER-ROTATING DEEP
CONVECTIVE BURSTS IN THE SOUTHWESTERN AND NORTHEASTERN QUADRANTS
HAVE EXPANDED DEEP CONVECTIVE COVERAGE IN THE LAST 3 HOURS,
SUGGESTING THAT INTENSIFICATION MAY BE ONGOING. THE INITIAL
INTENSITY IS SET AT 45 KT BASED ON A BLEND OF AGENCY DVORAK
ESTIMATES.

INITIAL WIND RADII BASIS: OTHER 

CURRENT STEERING MECHANISM: MID- TO UPPER-LEVEL RIDGE WEST OF
TAIWAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 37 KTS AT 241730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   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 09W (SAOLA) APPEARS TO BE
UNDERGOING A GRADUAL PROCESS OF VORTEX ALIGNMENT, AFTER BEING
TILTED FOR THE PAST 24 HOURS. THE MID- TO UPPER-LEVEL RIDGE TO THE
NORTHWEST WILL CONTINUE PUSHING THE STORM GENERALLY SOUTHWARD JUST
OFFSHORE OF EASTERN LUZON, EVENTUALLY PUTTING SOME DISTANCE BETWEEN
THE STORM AND THE NORTHERLY SHEAR BELT THAT IS CURRENTLY IMPACTING
THE VORTEX. THE PRESENCE OF A COMPACT CORE WIND FIELD OVER OCEAN
HEAT CONTENT VALUES IN EXCESS OF 100 KJ PER SQUARE CENTIMETER,
COMBINED WITH THE EXPECTED REDUCTION IN VERTICAL SHEAR OVER THE
NEXT 24-48 HOURS, MAKES RAPID INTENSIFICATION A DISTINCT
POSSIBILITY. THE JTWC FORECAST MAKES SAOLA A TYPHOON BY 24 HOURS.
DURING THE 24-48 HOUR PERIOD, A REDUCTION IN THE INTENSIFICATION
RATE IS FORECAST DUE TO PROXIMITY TO THE HIGH TERRAIN OF EASTERN
LUZON CAUSING DISRUPTIONS TO THE INNER CORE, ALONG WITH THE
POSSIBILITY OF MILD OCEAN COOLING DUE TO THE VERY SLOW TRACK.
HOWEVER, THE ENVIRONMENT WILL REMAIN FAVORABLE AND OCEAN HEAT
CONTENT HIGH, SO INTENSIFICATION IS EXPECTED TO GENERALLY CONTINUE
THROUGHOUT THE FORECAST PERIOD SO LONG AS THERE IS NOT TOO MUCH
LAND INTERACTION. ONCE SAOLA MOVES FAR ENOUGH SOUTH, THE INFLUENCE
OF THE RIDGE TO ITS NORTHWEST WILL WANE, AND THE SOUTHWESTERLY
MONSOONAL FLOW BELT THROUGH THE PHILIPPINES WILL BEGIN PUSHING THE
STORM BACK NORTHWARD, FORMING A SORT OF SLOW LOOPING TRACK. A TURN
NORTHWESTWARD IS EXPECTED BY MOST DYNAMICAL MODEL GUIDANCE BY
96-120 HOURS DUE TO THE SUBTROPICAL RIDGE OFF OF JAPAN, BUT MODEL
SPREAD IS QUITE HIGH DURING THIS TIME. THIS IS DUE TO THE GENERALLY
WEAK STEERING CURRENTS DURING MOST OF THE FORECAST PERIOD, ALONG
WITH THE POSSIBILITY OF A SEPARATE, LARGE TROPICAL CYCLONE
DEVELOPING ABOUT 1000 NM EAST OF 09W (SAOLA) IN 3 TO 5 DAYS, WHICH
MAY IMPACT THE STEERING FLOW FOR SAOLA IN AN UNCERTAIN WAY.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS FAIRLY CLOSE TO THE
MULTI-MODEL CONSENSUS, WHICH HAS SIGNIFICANT SPREAD IN THE 72-120
HOUR RANGE. THE ENSEMBLE ENVELOPES OF THE ECMWF AND GFS ENSEMBLES
ARE ALSO RATHER WIDE DURING THAT PERIOD, CONTRIBUTING TO LOWER THAN
AVERAGE CONFIDENCE. THE JTWC INTENSITY FORECAST IS SLIGHTLY ABOVE
THE MULTI-MODEL CONSENSUS, STICKING CLOSE TO A BLEND OF HAFS,
COAMPS-TC, GFS, AND ECMWF.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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