WDPN33 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (TORAJI) WARNING NR 
014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.8N 117.5E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 238 NM SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
IRREGULAR SHAPED DENSE OVERCAST FEATURE, DISPLACED TO THE WEST OF
THE PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC). THE LACK
OF ANY SIGNIFICANT CONVECTION IN THE EIR AND THE DRY AIR SEEN IN
THE TOTAL PRECIPITABLE WATER (TPW) LOOP SUGGESTS A SIGNIFICANT
WEDGE OF DRY AIR IS PRESENT IN THE EASTERN PORTION OF THE
CIRCULATION. A 121036Z SSMIS 37GHZ MICROWAVE IMAGE REVEALED A
MICROWAVE EYE FEATURE, COMPLETELY CLOSED BUT VERY WEAK ON THE
SOUTHEASTERN SIDE WHICH FACES THE SHEAR VECTOR. OTHERWISE, THE
MICROWAVE IMAGERY CONFIRMS THE HIGHLY ASYMMETRIC NATURE OF THE
CONVECTIVE STRUCTURE, WITH THE BULK OF THE DEEP CONVECTION TO THE
NORTH AND WEST OF THE LLCC, ORGANIZED INTO A LARGE COMMA-HEAD. THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON AN
EXTRAPOLATION OF THE MICROWAVE FEATURES NOTED ABOVE. THE INITIAL
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, HEDGED SLIGHTLY
HIGHER THAN THE BULK OF THE SUBJECTIVE AND OBJECTIVE ESTIMATES
NOTED ABOVE DUE TO PERSISTENCE. THE WIND FIELD CONTINUES TO EXPAND,
ESPECIALLY TO THE NORTHWEST, WITH SURFACE OBSERVATIONS FROM PRATAS
ISLAND NOW SHOWING SUSTAINED NORTHEASTERLY WINDS OF 41 KNOTS. THE
ENVIRONMENT REMAINS MARGINAL, WITH LOW VWS, WARM SSTS AND GOOD
POLEWARD OUTFLOW BEING OFFSET BY THE TILTED NATURE OF THE VORTEX
AND A WEDGE OF DRY MID-LEVEL AIR WHICH IS CLEARLY BEING INGESTED
INTO THE EASTERN PART OF THE VORTEX FROM THE SOUTH.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   DEMS: T4.0 - 65 KTS
   CIMSS ADT: 35 KTS AT 121130Z
   CIMSS AIDT: 35 KTS AT 121130Z
   CIMSS D-MINT: 37 KTS AT 121038Z
   CIMSS D-PRINT: 39 KTS AT 121230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 (TS) 26W WILL CONTINUE TO TRACK
TOWARDS THE NORTHWEST FOR THE NEXT 12 TO 24 HOURS, ALONG THE
SOUTHWESTERN SIDE OF THE STEERING RIDGE TO THE NORTH-NORTHEAST.
SHORTLY AFTER TAU 24, THE STEERING GRADIENT IS EXPECTED TO WEAKEN
DUE TO DEVELOPMENT OF A WEAKNESS OR BREAK IN THE RIDGING PATTERN.
TS 24W WILL SLOW DOWN AS IT APPROACHES THIS INFLECTION POINT JUST
SOUTH OF HONG KONG AND BEGIN TO TRACK SLOWLY TOWARDS THE WEST.
SIMULTANEOUS TO THIS SLOW-DOWN AND TURN TOWARDS THE WEST, THE
ENVIRONMENT WILL SIGNIFICANTLY DEGRADE. IN THE FIRST 24 HOURS OF
THE FORECAST, TS 24W MAY BE ABLE TO INTENSIFY SLIGHTLY, IF IT CAN
OVERCOME THE INFLUENCE OF THE DRY AIR CURRENTLY BEING PULLED INTO
THE SYSTEM FROM THE SOUTH. SOME OF THE MODELS SUGGEST THE SYSTEM
COULD ISOLATE ITSELF AND THUS BE ABLE TO SUSTAIN A BRIEF PERIOD OF
INTENSIFICATION UP TO 50 KNOTS. SHORTLY AFTER TAU 24 HOWEVER,
MID-LEVEL SOUTHWESTERLY SHEAR BEGINS TO PICK UP, WHICH MARKS THE
START OF A RAPID WEAKENING PHASE. BY TAU 36, DEEP-LAYER
SOUTHWESTERLY SHEAR IS EXPECTED TO APPROACH 30 KNOTS, WHICH WILL
COMPLETELY DECAPITATE THE VORTEX. AT THE SAME TIME, A MASSIVE
INFLUX OF DRY AIR WILL ENGULF THE SYSTEM. AS THE VORTEX SHALLOWS
OUT AND RAPIDLY WEAKENS, IT TURNS TOWARDS THE SOUTHWEST, THEN SOUTH
BY THE END OF THE FORECAST PERIOD. DISSIPATION BELOW WARNING
CRITERIA IS FORECAST NO LATER THAN TAU 72, TO THE EAST OF HAINAN.

MODEL DISCUSSION: TRACK GUIDANCE IS IN OVERALL GOOD AGREEMENT ON
THE OVERALL TRACK SCENARIO. CROSS-TRACK SPREAD HAS REMAINED VERY
CONSISTENT WITH THE PREVIOUS MODEL RUN, GRADUALLY OPENING UP TO
150NM BY TAU 72. THE NAVGEM REMAINS THE SOUTHERN OUTLIER, WHILE THE
JGSM SITS ON THE NORTHERN EDGE OF THE ENVELOPE. THE JGSM IS THE
ONLY MODEL SHOWING A LANDFALL IN NORTHEAST HAINAN BY THE END OF THE
FORECAST PERIOD, WITH THE REMAINDER OF THE GUIDANCE KEEPING THE
REMNANT VORTEX WELL OFFSHORE TO THE EAST. THE JTWC FORECAST IS
CONSISTENT WITH THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD,
WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN VERY GOOD AGREEMENT,
WITH VERY LITTLE (LESS THAN 5 KNOTS) SPREAD THROUGH THE FORECAST
PERIOD, LENDING HIGH CONFIDENCE TO THE JTWC FORECAST. 

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