WDPN31 PGTW 211500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (WIPHA) WARNING NR 
013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.1N 108.3E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 135 NM EAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY REVEALS A LARGE,
SLIGHTLY ASYMMETRICAL CENTRAL DENSE OVERCAST (CDO) FEATURE
ASSOCIATED WITH TROPICAL STORM (TS) 09W (WIPHA), WITH COLDEST CLOUD
TOPS REACHING -82.7 C. THE INITIAL POSITION IS DETERMINED WITH MEDIUM 
CONFIDENCE BASED ON RADAR IMAGERY, AS WELL AS EXTRAPOLATION FROM A 
211047Z F16 SSMIS MICROWAVE SUITE, INDICATING VORTEX TILT BETWEEN THE 
37 GHZ AND 89 GHZ. INITIAL INTENSITY IS ESTIMATED AT 50 KTS WITH 
MEDIUM CONFIDENCE, SUPPORTED BY PERSISTENT DEEP CENTRAL CONVECTION, 
AGENCY DVORAK FIXES, AND OBJECTIVE SATELLITE INTENSITY ESTIMATES 
LISTED BELOW. ENVIRONMENTAL ANALYSIS DEPICT A MARGINALLY CONDUCIVE 
SETUP FOR FURTHER DEVELOPMENT, CHARACTERIZED BY VERY WARM (30-31 C) 
SEA SURFACE TEMPERATURES (SST), MODERATE EQUATORWARD UPPER-LEVEL 
OUTFLOW, ABUNDANT MOISTURE IN THE ATMOSPHERIC COLUMN, OFFSET BY HIGH 
NORTHEASTERLY VERTICAL WIND SHEAR (VWS) CURRENTLY ANALYZED AT 25-30 
KTS.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHEASTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) LOCATED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS ADT: 49 KTS AT 211130Z
   CIMSS D-MINT: 53 KTS AT 211047Z
   CIMSS D-PRINT: 56 KTS AT 211210Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 25-30 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: PROXIMITY TO LAND

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: TS 09W IS FORECAST TO CONTINUE TRACKING
WEST-SOUTHWESTWARD, STEERED BY A WEAK SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTHEAST. AS THE SYSTEM REMAINS OVER VERY WARM
SSTS OF THE GULF OF TONKIN, SLIGHT INTENSIFICATION IS POSSIBLE WITH
PEAK SUSTAINED WINDS REACHING 55 KTS WITHIN THE NEXT 6-12 HOURS,
BEFORE TERRAIN INTERACTION STARTS AFFECTING THE WIND FIELD AND
ULTIMATELY STRUCTURE OF THE VORTEX. ADDITIONALLY, THE ONGOING
IMPACT OF HIGH VWS WILL IMPOSE A LIMIT ON POTENTIAL STRENGTHENING.
LANDFALL IS FORECAST TO OCCUR SOON AFTER TAU 12, RESULTING IN A
STEADY DEGRADATION OF THE LOW-LEVEL CIRCULATION OVER LAND, DUE TO
THE INTERACTION WITH THE COMPLEX TERRAIN OF NORTHERN VIETNAM AND
INCREASINGLY HOSTILE SHEAR. COMPLETE DISSIPATION IS ANTICIPATED BY
OR BEFORE TAU 48.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE EXHIBITS STRONG CONSENSUS 
ON THE SYNOPTIC TRACK SCENARIO, WITH A CROSS-TRACK SPREAD OF 
APPROXIMATELY 15 NM AT LANDFALL JUST EAST OF HANOI, VIETNAM. THE JTWC 
TRACK FORECAST IS THEREFORE POSITIONED NEAR THE MULTI-MODEL CONSENSUS 
WITH HIGH CONFIDENCE. INTENSITY GUIDANCE REMAINS IN GOOD AGREEMENT AS 
WELL, HOWEVER WITH NONE OF THE GUIDANCE MODELS INDICATING SHORT-TERM 
INTENSIFICATION. JTWC INTENSITY FORECAST IS THEREFORE HELD 5-10 KTS 
ABOVE CONSENSUS DUE TO THE MARGINALLY FAVORABLE CONDITIONS IN THE 
NEAR-TERM MARITIME ENVIRONMENT OF THE NORTHERN GULF OF TONKIN. AS SOON 
AS THE SYSTEM MAKES LANDFALL, JTWC INTENSITY FORECAST TREND CLOSELY 
FOLLOWS THAT OF THE MULTI-MODEL CONSENSUS.

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