WDPN31 PGTW 200300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (RAI) WARNING NR 029//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.3N 110.9E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 353 NM SOUTH-SOUTHWEST OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AS THE SUN HAS RISEN OVER TY 28W, IT HAS REVEALED A RAPIDLY
WEAKENING CYCLONE, THOUGH THE CENTRAL CIRCULATION APPEARS TO BE
RELATIVELY INTACT. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS A WELL DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) WITH A
SMALL POCKET OF FLARING CONVECTION BLOOMING NEAR THE ASSESSED
CENTER AND BEING SHEARED TO THE NORTH, WHILE THE REMAINDER OF THE
CIRCULATION IS DEVOID OF SIGNIFICANT CONVECTION. A 192247Z SSMIS
37GHZ MICROWAVE IMAGE SHOWED A WELL DEFINED LOW EMISSIVITY REGION
IDENTIFYING THE LLCC, WITH SHALLOW BANDING TO THE EAST AND SOUTH,
WRAPPING INTO THE TIGHT CIRCULATION CENTER. EXTRAPOLATION OF THE
MICROWAVE IMAGERY PROVIDED HIGH CONFIDENCE TO THE INITIAL POSITION.
THE INITIAL INTENSITY IS A BIT MORE TRICKY DUE TO THE VERY RAPID
UNRAVELING OF THE SYSTEM. AGENCY FIXES RANGE FROM A POSITION ONLY
FIX FROM KNES, TO RJTD T5.5. MEANWHILE, ADT WAS T4.7 USING THE
SHEAR METHOD, THROUGH THE RAW ADT WAS ONLY T1.5. SATCON WAS TOOL
OLD FOR USE IN THIS ANALYSIS, AND THE AI ADJUSTED ADT WAS 63 KNOTS.
THE INITIAL INTENSITY IS THUS SET AT A GENEROUS 70 KNOTS, BASED ON
A BLEND OF THE AVAILABLE DATA WITH LOW CONFIDENCE. THE SYSTEM IS
MOVING INTO AN EVEN MORE UNFAVORABLE ENVIRONMENT, WITH SSTS BELOW
25C, MODERATE VWS AND DRY AIR ENTRAINMENT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: GRADIENT BETWEEN MID-LATITUDE TROUGH TO
THE WEST AND WESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE
(STR) TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T5.5 - 102 KTS
   CIMSS ADT: 84 KTS AT 192340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 20-25 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING. HOWEVER THE WARNING HAS
BEEN TRUNCATED TO 48 HOURS. 

FORECAST DISCUSSION: TY 28W CONTINUES ITS PRECIPITOUS WEAKENING
TREND. THE SYSTEM IS FORECAST TO CONTINUE TRACKING NORTHEAST
THROUGH THE NEXT 12 HOURS THEN TURN EASTWARD IN A GRACEFUL ARC
THROUGH TAU 48. AS THE SYSTEM WEAKENS AND THE LOW LEVEL CENTER
BECOMES EXPOSED, THE SYSTEM WILL SLOW DOWN AND TURN EASTWARD UNDER
THE INFLUENCE OF THE LOWER LEVEL FLOW. SHEAR IS ALREADY AT 20 KNOTS
OR SLIGHTLY HIGHER BASED ON THE CIMSS ANALYSIS, AND WILL ONLY GET
WORSE FROM HERE ON OUT. BY TAU 12 SHEAR IS EXPECTED TO BE ABOVE 35
KNOTS AS THE SYSTEM STARTS TO FEEL THE SOUTHERN SIDE OF THE STRONG
WESTERLIES PRESENT IN A BAND OVER CENTRAL CHINA. BY TAU 24, IF NOT
BEFORE, THE SHEAR WILL DECAPITATE TY 28W, EXPOSE THE LLCC AND
INITIATE THE SYSTEMS DEMISE. THE RESIDUAL CIRCULATION WILL TAKE
SOME TIME TO SPIN DOWN TO LESS THAN 25 KNOTS, BUT NEVERTHELESS, IT
IS EXPECTED TO FULLY DISSIPATE BELOW WARNING THRESHOLD NO LATER
THAN TAU 48, TO THE SOUTHWEST OF TAIWAN. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH
THE FORECAST PERIOD, THOUGH SOME ALONG-TRACK SPREAD IS INTRODUCED
BY TAU 48 AS THE MODELS STRUGGLE WITH THE DISSIPATING VORTEX. THE
JTWC FORECAST REMAINS CONSISTENT WITH THE PREVIOUS FORECAST AND
TRACKS THE LEFT SIDE OF THE GUIDANCE ENVELOPE THROUGH TAU 36 THEN
MOVES TO THE RIGHT SIDE BY TAU 48 AS THE BULK OF THE GUIDANCE IS
MISSING THE TURN SOUTHEASTWARD. OVERALL CONFIDENCE IS MEDIUM DUE TO
THE UNCERTAINTY IN THE ULTIMATE DISSIPATION TIMELINE AND THE IMPACT
OF THE LOW-LEVEL FLOW ON THE REMNANT VORTEX AFTER TAU 36. INTENSITY
GUIDANCE IS IN GOOD AGREEMENT, AND THE JTWC FORECAST IS RIGHT DOWN
THE MIDDLE OF THE ENVELOPE, WITH MEDIUM CONFIDENCE. 

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