WDPN31 PGTW 182100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (RAI) WARNING NR 024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.5N 112.2E
   INITIAL INTENSITY: 145 KTS
   GEOGRAPHIC REFERENCE: 309 NM SOUTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 33 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TY RAI HAS UNDERGONE RAPID INTENSIFICATION OVER THE PAST 12 HOURS
WHICH WAS NOT PREVIOUSLY FORECASTED. ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY DEPICTS A BROAD, SYMMETRIC SYSTEM WITH A
WELL DEFINED EYE ABOUT 21 NM IN DIAMETER. TY 28W IS IN A FAVORABLE
ENVIRONMENT WITH STRONG WESTWARD AND POLEWARD OUTFLOW ALOFT, LOW
(10-15 KTS) VERTICAL WIND SHEAR, AND WARM (27-28 C) SEA SURFACE
TEMPERATURES. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON EYE POSITION VISIBLE IN EIR IMAGERY. THE INITIAL INTENSITY
OF 145 KTS IS SET WITH MEDIUM CONFIDENCE DUE TO LACK OF MICROWAVE
IMAGERY OVER THE PAST 9 HOURS AND BASED ON STRUCTURE NOTED IN
AFOREMENTIONED EIR IMAGERY. IN ADDITION, THE INITIAL INTENSITY IS
ALIGNED WITH MULTI-AGENCY AND AUTOMATED DVORAK ESTIMATES. 

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS
   KNES: T7.0 - 140 KTS
   RJTD: T7.0 - 140 KTS
   CIMMS SATCON: 131 KTS AT 181427Z
   CIMSS ADT: 155 KTS AT 181910Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG WESTWARD 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 STR AXIS OVER THE NEXT 12 HOURS.
AFTER TAU 12, THE SYSTEM WILL CROSS OVER RELATIVELY COOLER SEA
SURFACE TEMPERATURES OF <26C AND BEGIN TO ENCOUNTER MODERATE (20-25
KT) VWS WHICH WILL CONTRIBUTE TO RAPIDLY WEAKEN THE SYSTEM. BY TAU
18, TY 28W WILL BEGIN TO ROUND THE RIDGE AXIS TO BEGIN ITS TRACK
NORTHEASTWARD AND WILL BEGIN TO EXPERIENCE UNFAVORABLE (>30 KTS)
VERTICAL WIND SHEAR. BY TAU 24, TY RAI WILL BE INTRODUCED TO DRIER
AIR FROM THE WEST, FURTHER DECREASING THE INTENSITY TO 50 KTS. BY TAU
48, THE SYSTEM WILL FALL UNDER THE INFLUENCE OF STRONG WESTERLIES AND
DISSIPATE COMPLETELY 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 33 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. THIS
LENDS HIGH CONFIDENCE TO THE JTWC FORECAST TRACK. 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 DUE TO THE SYSTEM ENTERING AN UNFAVORABLE
ENVIRONMENT THROUGHOUT THE FORECAST PERIOD. THE JTWC INTENSITY
FORECAST IS HEDGED SLIGHTLY HIGHER THAN MODEL CONSENSUS.

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