WDPN31 PGTW 170300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (RAI) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.0N 121.1E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 276 NM SOUTH OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN AREA OF FLARING DEEP CONVECTION EMBEDDED WITHIN A SLIGHTLY ELONGATED AND DISORGANIZED AREA OF HIGH-LEVEL CIRRUS BLOWOFF. THE MOST RECENT MICROWAVE IMAGERY AVAILABLE WAS FROM 162048Z AND DEPICTED A SMALL MICROWAVE EYE FEATURE, PARTICULARLY IN THE COLOR COMPOSITE 89GHZ IMAGE. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON BOTH THE CLOSE GROUPING OF AGENCY FIXES AND EXTRAPOLATION OF THE MICROWAVE EYE FEATURE. THE INITIAL INTENSITY IS ASSESSED AT A GENEROUS 100 KNOTS, RIGHT AT THE AVERAGE OF AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T5.5 AND THE ADT VALUE OF T5.3. THE SYSTEM HAS TAKEN A SLIGHTLY MORE WESTWARD COURSE AFTER MOVING INTO THE SULU SEA, BUT OVERALL REMAINS TRACKING WEST ALONG THE SOUTHERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) TO THE NORTH. ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE FOR DEVELOPMENT, WITH LOW TO MODERATE VERTICAL WIND SHEAR, GOOD WESTWARD AND POLEWARD OUTFLOW AND WARM SSTS. 

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS 
   RJTD: 
   KNES: T5.5 - 102 KTS
   CIMSS ADT: 93 KTS AT 162340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG WESTWARD
   OTHER FACTORS: MODERATE POLEWARD OUTFLOW

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 28W CONTINUES TO TRACK WESTWARD ALONG THE SOUTHERN SIDE OF A DEEP STR TO THE NORTH. THE SYSTEM IS FORECAST TO PASS OVER PALAWAN ISLAND WITHIN THE NEXT 12 HOURS, THEN GRADUALLY TURN NORTHWESTWARD IN A GRACEFUL ARC THROUGH TAU 48, WHERE IT WILL LIE JUST EAST OF CENTRAL VIETNAM. AS THE STEERING RIDGE RETREATS EASTWARD AFTER TAU 48, THE SYSTEM WILL TURN SHARPLY NORTH, THEN NORTHEAST THROUGH TAU 96. AS THE SYSTEM WEAKENS IT WILL COME UNDER THE STEERING INFLUENCE OF THE LOW LEVEL FLOW AND TURN EAST-SOUTHEAST BY TAU 120. NOW THAT TY 28W HAS EMERGED BACK OVER THE WARM WATERS OF THE SULU SEA, THE IMPROVED OUTFLOW, WARM SSTS AND REDUCED VWS WILL LEAD TO A PERIOD OF INTENSIFICATION, PEAKING AT 110 KNOTS AT TAU 36. THIS WILL BE THE HIGH WATER MARK, AS AFTER THE SYSTEM TURNS POLEWARD, DRAMATICALLY INCREASED SHEAR, DECREASED SSTS, AND DRY AIR ENTRAINMENT 
WILL CONSPIRE TO DECAPITATE AND SMOTHER THE SYSTEM AND ULTIMATELY LEAD TO ITS DEMISE NO LATER THAN TAU 120. 

MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN GOOD AGREEMENT THROUGH TAU 48, THEN NOT SURPRISINGLY BEGINS TO DIVERAGE DURING THE RECURVE. WHILE THE MODELS DO SPREAD AFTER TAU 48, OVERALL THE UNCERTAINTY IS FAIRLY MODEST, WITH ALL MODELS, WITH THE EXCEPTION OF GALWEM, CONSTRAINED WITHIN A 100NM ENVELOPE, EVEN AT TAU 120. OVERALL CONFIDENCE IS HIGH THROUGH TAU 48, BUT DECREASES TO MEDIUM THEREAFTER IN LIGHT OF THE CLIMATOLOGICAL UNCERTAINTY SURROUNDING RECURVE EVENTS, ESPECIALLY WHEN COMBINED WITH RAPID DISSIPATION. THE INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM WILL INTENSITY SLIGHTLY AS IT MOVES INTO THE SOUTH CHINA SEA, THEN RAPIDLY WEAKEN AFTER THE ONSET OF THE HIGH SHEAR AFTER TAU 48. THE JTWC FORECAST LIES ALONG THE HIGH END OF THE GUIDANCE PACKAGE, WITH MEDIUM CONFIDENCE. 

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