WDPN31 PGTW 132100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 28W (RAI) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 6.8N 138.6E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 165 NM SOUTH OF YAP
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CENTRAL DENSE OVERCAST (CDO) FEATURE, WITH VORTICAL HOT TOWERS
(VHTS) WITH CLOUD TOP TEMPERATURES APPROACHED -100C FLARING NEAR
THE ASSESSED CENTER POSITION. THE HIGH RESOLUTION EIR DATA SHOWS
IMPRESSIVE GRAVITY WAVES EMANATING OUTWARD FROM THE CENTRAL UPDRAFT
REGION, WHICH ALSO HELPS TO OUTLINE THE PRESENCE OF SOME MID TO
HIGH-LEVEL EASTERLY SHEAR, AS THE GRAVITY WAVES COME TO AN ABRUPT
STOP ABOUT 100NM EAST OF THE CENTER. AS EXPECTED WITH A CDO
FEATURE, THE LLCC IS DIFFICULT TO NAIL DOWN WITH ANY CERTAINTY. THE
ONLY MICROWAVE IMAGE IN THE PAST 13 HOURS HAS BEEN A 131649Z
PARTIAL AMSR2, WHICH SHOWED AN IMPRESSIVE AMOUNT OF CONVECTION IN
THE CORE, AND A FALSE MICROWAVE EYE IN THE 37GHZ BAND, SO THE
INITIAL POSITION IS STILL UNCERTAIN AND ASSESSED WITH LOW
CONFIDENCE. THE INITIAL INTENSITY HAS BEEN INCREASED TO 45 KNOTS,
HEDGED CLOSER TO THE PGTW AND KNES SUBJECTIVE FIXES AND THE ADT AND
SATCON OBJECTIVE ESTIMATES, WITH MEDIUM CONFIDENCE.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 43 KTS AT 131605Z
   CIMSS ADT: 45 KTS AT 131740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND 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 28W IS FORECAST TO CONTINUE
TRACKING ALONG THE SOUTH-SOUTHWEST PERIPHERY OF THE DEEP-LAYER STR
THROUGH THE FORECAST PERIOD. SOME SLOWING IS EXPECTED AS IT CROSSES
THROUGH THE PHILIPPINES ARCHIPELAGO, BUT OTHERWISE NO SIGNIFICANT
CHANGES IN THE TRACK ARE EXPECTED. THE SYSTEM IS EXPECTED TO MOVE
THROUGH THE SOUTHERN PHILIPPINES BETWEEN TAU 60 AND TAU 96, THEN
EMERGE INTO THE SOUTH CHINA SEA JUST NORTH OF PALAWAN. OVER THE
PAST SIX HOURS, TS 28W HAS CONTINUED TO RAPIDLY CONSOLIDATE AND IS
SHOWING THE FIRST HINTS OF POTENTIAL RAPID INTENSIFICATION, WITH
THE OVERNIGHT DEVELOPMENT OF A CENTRAL DENSE OVERCAST FEATURE WITH
VERY COLD OVERSHOOTING TOPS. HOWEVER, AT ANALYSIS TIME, THE VHTS
WITH THE COLDEST CLOUD TOPS CURRENTLY LACK ANY SIGN OF ROTATION,
WHICH WOULD BE A CLEAR INDICATOR THAT THE CORE WAS CONSOLIDATING.
GFS AND HWRF MODEL FIELDS SUGGEST THE POSSIBILITY OF A DUAL
VORTICITY CENTER SETUP, WITH ONE NEAR THE STRONG UPDRAFT REGION IN
THE EIR, AND ANOTHER JUST TO THE EAST. THE DEARTH OF MICROWAVE AND
SCATTEROMETER DATA PRECLUDES VERIFICATION AT PRESENT, BUT IF THE
MODELS REPRESENT ACTUAL CONDITIONS, THIS COULD HINDER THE
DEVELOPMENT SOMEWHAT, AT LEAST IN THE NEAR-TERM. THE MODELS SUGGEST
FULL CONSOLIDATION OF THESE TWO AREAS WITHIN THE NEXT 6 TO 12
HOURS. ONCE THE CORE FULLY CONSOLIDATES, EXPECT RAPID
INTENSIFICATION TO COMMENCE IN EARNEST. ENVIRONMENTAL CONDITIONS
ARE FAVORABLE, WITH MODERATE EASTERLY VWS, VERY WARM SSTS AND
ROBUST, NEAR-RADIAL, OUTFLOW ALOFT. WHILE EASTERLY SHEAR IS
FORECAST TO REMAIN IN THE 15-20 KNOT RANGE, THE SETUP IS RIPE FOR A
RAPID INTENSIFICATION UNDER MODERATE SHEAR SCENARIO, AND THUS THE
VWS IS NOT EXPECTED TO SEVERELY IMPACT THE SYSTEM THROUGH TAU 48.
THE RATE OF INTENSIFICATION COULD SLOW SLIGHTLY AFTER TAU 48, AS
THE POLEWARD OUTFLOW CHANNEL IS REDUCED OR CUT OFF, GENERATING LESS
DIVERGENCE ALOFT, AND ONCE THE SYSTEM MOVES INTO THE PHILIPPINE
ISLANDS, LAND INTERACTION WILL SERVE TO WEAKEN THE SYSTEM DOWN TO
ABOUT 85 KNOTS. INCREASED OUTFLOW ALOFT WILL OFFSET SLIGHTLY HIGHER
VWS BY TAU 120, AND THE SYSTEM IS EXPECTED TO MAINTAIN INTENSITY
THROUGH THIS PERIOD. 

MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN GOOD AGREEMENT WITH
LESS THAN 100NM SPREAD THROUGH TAU 96, INCREASING SLIGHTLY TO 150NM
BY TAU 120. THE GFS AND ECMWF ENSEMBLE RUNS HAVE COME INTO MUCH
BETTER AGREEMENT SINCE THE OVERNIGHT RUNS, AND NOW ARE SHOWING
ROUGHLY THE SAME AMOUNT OF SPREAD AS THE DETERMINISTIC MEMBERS OF
THE CONSENSUS. THE JTWC FORECAST REMAINS CONSISTENT WITH THE
PREVIOUS FORECAST WITH HIGH CONFIDENCE. INTENSITY GUIDANCE HAS
SHOWN AND MARKED AND SIGNIFICANT UPTICK SINCE THE PREVIOUS RUN. ALL
RAPID INTENSIFICATION AIDS HAVE NOW BEEN TRIGGERED, WITH THE RIPA
INDICATING A PEAK INTENSITY OF 115 KNOTS BY TAU 48. THE REMAINDER
OF THE CONSENSUS GUIDANCE IS LESS BULLISH, PEAKING BETWEEN 75-95
KNOTS, FOLLOWED BY A WEAKENING WHILE CROSSING THE PHILIPPINES AND
MODEST INTENSIFICATION IN THE SOUTH CHINA SEA. THE JTWC FORECAST
FOLLOWS THE RAPID INTENSIFICATION GUIDANCE THROUGH TAU 36, TO A
PEAK OF 100 KNOTS BEFORE LEVELING OFF TO 85 KNOTS THROUGH TAU 120.
THE JTWC FORECAST LIES 15-20 KNOTS ABOVE THE CONSENSUS MEAN.
CONFIDENCE IS MEDIUM THROUGH TAU 72, AND LOW THEREAFTER DUE TO THE
LARGE SPREAD AND UNCERTAINTY IN THE GUIDANCE. 

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