WDPN31 PGTW 190900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (WIPHA) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.5N 118.9E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 284 NM EAST-SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A MAINLY
OBSCURED LOW-LEVEL CIRCULATION CENTER WITH SYNOPTIC SCALE SPIRAL BANDS 
OF DEEP CONVECTION, ASSOCIATED WITH TROPICAL STORM (TS) 09W (WIPHA). 
STRONG EQUATORWARD OUTFLOW CAN BE OBSERVED ON THE WATER VAPOR AND 
VISIBLE SPECTRUM SATELLITE IMAGERY. THE INITIAL POSITION IS PLACED 
WITH MEDIUM CONFIDENCE DUE TO INTENSE CONVECTIVE OBSCURATION, AND IS 
BASED ON 190552Z ATMS MICROWAVE IMAGE, IN CONJUNCTION WITH THE POSITION 
EXTRAPOLATION FROM A 190211Z METOP-C UHR ASCAT PASS. THE INITIAL 
INTENSITY OF 50 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON A 
COMBINATION OF AGENCY DVORAK FIXES AND OBJECTIVE ESTIMATES LISTED 
BELOW, SUPPORTED BY THE AFOREMENTIONED UHR ASCAT PASS DATA. ADDITIONAL 
ENVIRONMENTAL ANALYSIS REVEALS FAVORABLE CONDITIONS, INCLUDING DEEP-
LAYER MOISTURE AVAILABLE THROUGHOUT THE ATMOSPHERIC COLUMN, WARM (29-
30 C) SEA SURFACE TEMPERATURES AND STRONG UPPER-LEVEL OUTFLOW, OFFSET 
ONLY BY A MODERATE TO HIGH (20-25 KTS) VERTICAL WIND SHEAR (VWS).

INITIAL WIND RADII BASIS: A 190214Z METOP-C ASCAT PASS

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 51 KTS AT 190600Z
   CIMSS ADT: 45 KTS AT 190530Z
   CIMSS AIDT: 42 KTS AT 190600Z
   CIMSS D-MINT: 47 KTS AT 190528Z
   CIMSS D-PRINT: 47 KTS AT 190630Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

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-NORTHWESTWARD
ALONG THE SOUTHWESTERN PERIPHERY OF A STR LOCATED TO THE NORTHEAST
OF THE SYSTEM. AFTER TAU 24, THE RIDGING IS EXPECTED TO BUILD AND
EXTEND FURTHER WEST, RESULTING IN THE CIRCULATION MAKING A SLIGHT TURN 
TOWARD THE WEST. DURING THAT TIME, THE SYSTEM WILL REMAIN WITHIN 
MOSTLY FAVORABLE ENVIRONMENT LEADING TO POTENTIAL INTENSIFICATION AND 
REACHING PEAK WIND SPEEDS OF 55-60 KTS BETWEEN TAUS 12 AND 24. AS THE 
RIDGING BUILDS, THE TRACK IS EXPECTED TO SHIFT WEST-SOUTHWESTWARD AND 
CONTINUE ALONG THE COASTLINE OF SOUTHERN CHINA, UNTIL THE SYSTEM 
REACHES NORTHEASTERN VIETNAM, WHERE IT IS EXPECTED TO MAKE LANDFALL. TS 
09W IS FORECAST TO BEGIN WEAKENING AFTER TAU 24, AS A RESULT OF TERRAIN 
INTERACTION AND SLIGHTLY INCREASING VWS, HOWEVER AS SOON AS THE TS 
REACHES THE GULF OF TONKIN, IT WILL ENCOUNTER EXCEPTIONALLY WARM (30-
31 C) SEA SURFACE TEMPERATURES. THIS WILL RESULT IN MAINTAINED OR 
POTENTIALLY SLIGHTLY INCREASED WIND SPEEDS MAXIMA. AFTERWARD HOWEVER, 
THE SYSTEM IS EXPECTED TO BEGIN DISSIPATING, SHORTLY AFTER LANDFALL 
EAST OF HANOI, VIETNAM. FULL DISSIPATION IS EXPECTED AROUND TAU 96.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT FOR THE SHORT TERM, AS WITNESSED BY A 65 NM CROSS-TRACK
SPREAD AT TAU 72, WITH MAJORITY OF THE MODELS ENCLOSED WITHIN A 30 NM
ENVELOPE. THE TWO OPPOSITE OUTLIERS ARE GALWEM, TAKING THE SYSTEM
ON A TRACK FURTHER NORTH, AND NAVGEM SUGGESTING A PASS CLOSER TO
HAINAN ISLAND. LONG TERM GUIDANCE IS NOT SIGNIFICANTLY WORSE, WITH
A CROSS-TRACK SPREAD OF JUST 110 NM AT TAU 96, HOWEVER THE FORECAST
CONFIDENCE IS REDUCED TO MEDIUM, DUE TO SOME MODELS (PAST RUNS OF
THE DETERMINISTIC GFS, AND GFS ENSEMBLE) INDICATING POTENTIAL FOR
THE SYSTEM TURNING AROUND AT OR SOON AFTER LANDFALL. INTENSITY 
GUIDANCE IS IN FAIR AGREEMENT, WITH MAJORITY OF THE MODELS SUGGESTING 
45-55 KTS FOR THE NEXT 24 HOURS, FOLLOWED BY WEAKENING AND EVENTUAL 
DISSIPATION. JTWC FORECAST IS LAID CLOSE TO THE MULTI-MODEL CONSENSUS 
THROUGHOUT THE FORECAST. LOW INTENSITY PREDICTION CONFIDENCE IS 
ASSOCIATED WITH THE SLIGHTLY INCREASED UNCERTAINTY IN REGARD TO THE 
TRACK OF THE SYSTEM AROUND THE TIME OF LANDFALL.

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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