WDPN31 PGTW 181500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (RAI) WARNING NR 023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.9N 113.5E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 390 NM SOUTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 29 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) DEPICTS A BROAD, 
SYMMETRIC SYSTEM THAT HAS DEVELOPED AN EYE ABOUT 25-30 NM IN 
DIAMETER. TY 28W IS IN A MARGINALLY FAVORABLE ENVIRONMENT WITH STRONG 
EQUATORWARD AND POLEWARD OUTFLOW ALOFT, MODERATE (15-25 KTS) VERTICAL 
WIND SHEAR, AND WARM (27-28 C) SEA SURFACE TEMPERATURES. THE INITIAL 
POSITION AND INITIAL INTENSITY OF 115 KTS IS BASED ON THE PGTW 
POSITION FIX AND DVORAK CURRENT INTENSITY ESTIMATE OF T6.0 (115 KTS).

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER 
SUBTROPICAL RIDGE TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   KNES: T6.5 - 127 KTS
   CIMSS ADT: 146 KTS AT 181210Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG EQUATORWARD AND POLEWARD

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: TY 28W IS EXPECTED TO CONTINUE A GENERALLY  
NORTHWEST TRACK AS IT APPROACHES THE SUBTROPICAL RIDGE AXIS OVER THE  
NEXT 12 HOURS. AFTER TAU 12, IT WILL CROSS INTO SEA SURFACE 
TEMPERATURES OF <26C WHICH WILL BEGIN TO RAPIDLY WEAKEN THE SYSTEM, 
WHICH WILL REMAIN OVER COOLER WATERS FOR THE REMAINDER OF THE 
FORECAST. AROUND TAU 24, TY 28W WILL BEGIN TO ROUND THE RIDGE AXIS 
AND BEGIN TO EXPERIENCE INCREASED VERTICAL WIND SHEAR (>30 KTS). BY 
TAU 48, THE SYSTEM WILL TURN NORTHEASTWARD AND BEGIN TO ENCOUNTER 
DRIER AIR FROM THE WEST, FURTHER DECREASING THE INTENSITY TO 50 KTS. 
FOR THE REMAINDER OF FORECAST, THE SYSTEM WILL TRACK NORTHEASTWARD 
UNDER THE INFLUENCE OF STRONG WESTERLIES AND DISSIPATE BY TAU 72.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE CONTINUES TO BE IN 
RELATIVELY GOOD AGREEMENT IN REGARDS TO THE NEAR PORTION OF THE 
FORECAST TRACK WITH ONLY A 30 NM CROSS-TRACK SPREAD AT TAU 24. THE 
SPREAD INCREASES AFTERWARDS BUT ALL MODELS AGREE ON THE SAME GENERAL 
TRACK DIRECTION FOR THE REMAINDER OF THE JTWC FORECAST PERIOD. 
THEREFORE, THE JTWC FORECAST TRACK IS PLACED CLOSE TO CONSENSUS. 
INTENSITY GUIDANCE IS IN GOOD AGREEMENT WITH ALL MODELS SHOWING THE 
SYSTEM AT CURRENT PEAK INTENSITY FOLLOWED BY A RAPID DECREASE IN 
INTENSITY FROM NOW UNTIL TAU 72. THE JTWC FORECAST INTENSITY IS 
PLACED CLOSE TO CONSENSUS. 

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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