WDPN31 PGTW 210900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (WIPHA) WARNING NR 
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.3N 109.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 174 NM EAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LOW-LEVEL 
CIRCULATION CENTER (LLCC) ASSOCIATED WITH TROPICAL STORM (TS) 09W 
(WIPHA) REEMERGING OVER THE NORTHEASTERN PORTION OF THE GULF OF 
TONKIN. AS THE SYSTEM TAPS INTO THE WARM (30-31 C) WATERS, THE SPIRAL 
BANDS OF DEEP CONVECTION ARE STARTING TO CONSOLIDATE AND ARE CURRENTLY 
FULLY OBSCURING THE LLCC. THE INITIAL POSITION IS THEREFORE PLACED 
WITH MEDIUM CONFIDENCE BASED ON RADAR IMAGERY, AS WELL AS 
EXTRAPOLATION FROM A PARTIAL 210223Z METOP-B ASCAT PASS. THE INITIAL 
INTENSITY OF 45 KTS IS ALSO ASSESSED WITH MEDIUM CONFIDENCE BASED ON 
SUSTAINED CONVECTIVE STRUCTURE ASSOCIATED WITH THE REEMERGENCE OVER 
WATER, COMBINED WITH THE AGENCY FIXES AND OBJECTIVE ESTIMATES LISTED 
BELOW. ENVIRONMENTAL ANALYSIS REVEALS A MARGINALLY FAVORABLE 
ENVIRONMENT, WITH AFOREMENTIONED WARM SEA SURFACE TEMPERATURES (SST), 
MODERATE EQUATORWARD OUTFLOW, OFFSET HOWEVER BY INCREASING 
NORTHEASTERLY SHEAR, CURRENTLY ASSESSED AT 20-25 KTS.

INITIAL WIND RADII BASIS: A 210223Z METOP-B ASCAT

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   CIMSS SATCON: 49 KTS AT 210700Z
   CIMSS ADT: 45 KTS AT 210530Z
   CIMSS AIDT: 41 KTS AT 210600Z
   CIMSS D-MINT: 46 KTS AT 210606Z
   CIMSS D-PRINT: 44 KTS AT 210630Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: PROXIMITY TO LAND

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TS 09W IS FORECAST TO TRACK WEST-SOUTHWESTWARD
UNDER THE WEAK INFLUENCE FROM A STR TO THE NORTHEAST. AS IT TRANSITS 
OVER THE VERY WARM WATERS OF THE GULF OF TONKIN IT IS EXPECTED TO 
SLIGHTLY INTENSIFY, REACHING 50-55 KTS WITHIN THE NEXT 12 HOURS. 
CONVECTIVE BANDING IS EXPECTED TO IMPROVE, HOWEVER IMPACTS FROM THE 
VWS WILL PLACE A CAP ON THE AMOUNT OF INTENSIFICATION. AFTERWARD, AS 
THE SYSTEM APPROACHES THE COAST OF NORTHERN VIETNAM, FURTHER 
INCREASING VWS AND THE IMPACTS FROM TERRAIN INTERACTION WILL RESULT IN 
GRADUAL WEAKENING. LANDFALL IS EXPECTED BETWEEN TAUS 12 AND 24, 
FOLLOWED BY STEADY WEAKENING AS THE SYSTEM MOVES FURTHER INLAND. FULL 
DISSIPATION IS EXPECTED AT OR BEFORE TAU 48.

MODEL DISCUSSION: NUMERICAL TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT, 
WITH A CROSS-TRACK SPREAD OF 40 NM AT THE TIME OF LANDFALL, WITH THE 
EXCEPTION OF JGSM, WHICH IS CURRENTLY PROJECTING A TRACK FURTHER SOUTH 
THAN THE REST OF THE GUIDANCE. ALL AVAILABLE MODELS PREDICT THAT TS 
09W WILL MOVE OVER LAND EAST OR SOUTHEAST OF HANOI AND TRANSIT 
WESTWARD AFTERWARD. JTWC TRACK IS LAID WITH HIGH CONFIDENCE AND CLOSE 
TO THE MULTI-MODEL CONSENSUS. INTENSITY IS ASSESSED WITH MEDIUM 
CONFIDENCE, AS NONE OF THE AVAILABLE MODELS INDICATE AN UPTICK IN 
INTENSITY OVER THE NEXT 12 HOURS, BUT SUGGEST SLIGHT WEAKENING, 
FOLLOWED BY A MORE RAPID INTENSITY DECREASE AFTER TAU 12. JTWC 
INTENSITY FORECAST IS ASSESSED 5-10 KTS HIGHER THAN THE CONSENSUS, DUE 
TO A RELATIVELY SMALL SCALE, BUT FAVORABLE IMPACTS OF THE ENVIRONMENT 
WITHIN THE NORTHERN GULF OF TONKIN.

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