WDPN31 PGTW 131500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (WUTIP) WARNING NR 
013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.8N 108.3E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 189 NM SOUTHEAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 01W (WUTIP) AS HAVING STAYED NEARLY STATIONARY OVER THE PAST
6 HOURS, STAYING WEST OF HAINAN. A 131102Z SSMIS 91 GHZ MICROWAVE
IMAGE SHOWS THE MICROWAVE EYE FEATURE WITH CONVECTIVE BANDING
SURROUNDING THE SOUTHERN SEMICIRCLE OF THE SYSTEM. CENTRAL
CONVECTION HAS BECOME A BIT LESS ORGANIZED COMPARED TO 6 HOURS AGO,
BUT THE CIRRUS FILAMENTS EXTENDING EQUATORWARD HAVE BECOME MORE
PRONOUNCED. ENVIRONMENTAL ANALYSIS INDICATES THAT 01W IS IN A
FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG EQUATORWARD OUTFLOW
ALOFT, LOW (10-15 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA
SURFACE TEMPERATURES. THE PROXIMITY TO LAND IS THE ONLY NEGATIVE
FACTOR AT THE MOMENT. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON ANIMATED RADAR IMAGERY AND THE MENTIONED SSMIS
MICROWAVE IMAGE. THE INITIAL INTENSITY OF 60 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND OBJECTIVE
INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTWARD EXTENSION OF A
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST.


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   DEMS: T4.0 - 65 KTS
   CIMSS ADT: 49 KTS AT 131110Z
   CIMSS AIDT: 57 KTS AT 131110Z
   CIMSS DPRINT: 60 KTS AT 131110Z
   CIMSS DMINT: 50 KTS AT 131101Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: TERRAIN INTERACTION WITH WESTERN HAINAN 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: 01W IS FORECAST TO BEGIN A NORTHWESTWARD TRACK
OVER THE NEXT 12 HOURS AS IT ROUNDS THE RIDGE AXIS. THE SYSTEM WILL
THEN CONTINUE ON A NORTHWESTWARD TRAJECTORY THROUGH THE REMAINDER
OF THE FORECAST PERIOD AS IT TRACKS ALONG THE WESTERN PERIPHERY OF
THE STR. LANDFALL IS FORECAST TO OCCUR JUST WEST OF THE LEIZHOU
PENINSULA BETWEEN TAU 18-24. REGARDING INTENSITY, 01W IS FORECAST
TO MAINTAIN ITS CURRENT INTENSITY OF 60 KTS THROUGH TAU 12 AND UP
UNTIL THE TIME OF LANDFALL DUE TO THE LOW VERTICAL WIND SHEAR AND
WARM WATERS WITHIN THE GULF OF TONKIN. HOWEVER, IF THE SYSTEM
MAINTAINS ITS SLUGGISH MOVEMENT, RAPID UPWELLING COULD CAUSE
WEAKENING OF THE VORTEX. AFTER LANDFALL, 01W WILL QUICKLY WEAKEN AS
TERRAIN INTERACTION DEGRADES THE SYSTEM. DISSIPATION IS FORECAST TO
OCCUR NEAR TAU 48 AS THE VORTEX ACCELERATES NORTHWESTWARD. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH A 60 NM CROSS-TRACK SPREAD AT TAU 24, NEAR THE TIME
OF LANDFALL. AFTER TAU 24, ALONG-TRACK SPREAD GREATLY INCREASES TO
AROUND 300 NM AS THE VORTEX BECOMES SHALLOW AND MOVES OFF TO THE
NORTHWEST. ECMWF IS THE FASTEST TRACKER WHILE GFS IS THE SLOWEST.
THE JTWC TRACK FORECAST IS PLACED WITH OVERALL HIGH CONFIDENCE,
THOUGH THERE IS SOME UNCERTAINTY NEAR THE END OF THE FORECAST
REGARDING TRACK SPEEDS. INTENSITY GUIDANCE IS IN MODERATE AGREEMENT
WITH HAFS-A AND GFS BOTH SUGGESTING WEAKENING FROM TAU 0 WHILE HWRF
SUGGESTS INTENSIFICATION TO 65 KTS AT TAU 12. ALL MODELS AGREE ON
WEAKENING AFTER TAU 12. THE JTWC INTENSITY FORECAST IS PLACED WITH
MEDIUM CONFIDENCE, CLOSE TO THE MULTI-MODEL CONSENSUS.

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