WDPN31 PGTW 130900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (WUTIP) WARNING NR 
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.7N 108.3E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 193 NM SOUTHEAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 01W (WUTIP) WITH CENTRALIZED CONVECTION BEGINNING TO ENCIRCLE
THE OBSCURED LOW-LEVEL CIRCULATION CENTER. SPIRAL BANDING HAS ALSO
BECOME MORE DEFINED OVER THE PAST 6 HOURS. ADDITIONALLY, VERTICAL
WIND SHEAR HAS LESSENED, ALLOWING FOR THE SYSTEM TO BECOME MORE
VERTICALLY ALIGNED. TRACK DIRECTION APPEARS TO BE SHIFTING TO A
MORE NORTHWARD TRAJECTORY, HINTING AT THE BEGINNING OF THE
NORTHWESTWARD TURN. 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 ENVIRONMENT IS SLIGHTLY HINDERED DUE TO
THE PROXIMITY OF THE SYSTEM TO LAND, AS IT IS NOW JUST OFF THE
WESTERN COAST OF HAINAN. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE ANIMATED MSI AND RADAR IMAGERY. THE INITIAL
INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. A
130258Z ASCAT UHR WIND SPEED IMAGE DEPICTED SLIGHTLY WEAKER WINDS
(AROUND 50 KTS) WITHIN THE SOUTHERN SEMICIRCLE BUT COULD BE
DEGRADED DUE TO THE PROXIMITY TO HAINAN.

INITIAL WIND RADII BASIS: 130300Z METOP-C SCATTEROMETER DATA 

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
   KNES: T4.0 - 65 KTS
   DEMS: T4.0 - 65 KTS
   CIMSS ADT: 57 KTS AT 130600Z
   CIMSS AIDT: 43 KTS AT 130600Z
   CIMSS DPRINT: 62 KTS AT 130600Z
   CIMSS DMINT: 68 KTS AT 130616Z

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

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: 01W IS FORECAST TO ROUND THE RIDGE AXIS OVER
THE NEXT 12 HOURS WITH A NORTHWESTWARD TURN. LANDFALL IS FORECAST
TO OCCUR JUST WEST OF THE LEIZHOU PENINSULA NEAR TAU 24. THE SYSTEM
WILL THEN CONTINUE ON A NORTHWESTWARD TRACK THROUGHOUT THE REMAINDER
OF THE FORECAST PERIOD AS IT TRAVELS FURTHER INLAND. REGARDING
INTENSITY, 01W IS FORECAST TO MAINTAIN INTENSITY, OR SLIGHTLY
INTENSIFY OVER THE NEXT 12 HOURS DUE TO THE OVERALL FAVORABLE
ENVIRONMENT WITHIN THE GULF OF TONKIN. SHEAR IS EXPECTED TO REMAIN
RIGHT AROUND 10 KTS THROUGH TAU 24. AS THE SYSTEM MAKES LANDFALL,
INCREASING TERRAIN INTERACTION WILL CAUSE THE VORTEX TO BEGIN
WEAKENING. 01W WILL THEN RAPIDLY WEAKEN AND ACCELERATE
NORTHWESTWARD OVER MAINLAND CHINA WITH DISSIPATION FORECAST TO
OCCUR AROUND TAU 48. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH A 65 NM CROSS-TRACK SPREAD AT TAU 24, WHEN THE
SYSTEM IS JUST OFF THE COAST. AT TAU 48, ALONG-TRACK SPREAD
SIGNIFICANTLY INCREASES TO AROUND 160 NM AS THE VORTEX SHALLOWS AND
ACCELERATES NORTHWESTWARD. THE GFS DETERMINISTIC IS THE SLOWEST
TRACKER WHILE ECMWF AND NAVGEM ARE THE FASTEST. OVERALL, THE JTWC
TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE, CLOSE TO THE MULTI-
MODEL CONSENSUS. INTENSITY GUIDANCE IS SPLIT, WITH HAFS-A AND GFS 
SUGGESTING WEAKENING FROM TAU 0 WHILE HWRF AND STATISTICAL DYNAMICAL 
MODELS SUGGEST A STEADY INTENSITY THROUGH TAU 24. ALL MODELS THEN 
AGREE ON WEAKENING AFTER TAU 24. THE JWC INTENSITY FORECAST IS PLACED 
CLOSER TO HWRF THROUGH TAU 24 AND THEN CLOSE TO CONSENSUS THROUGH TAU 
48 WITH MEDIUM CONFIDENCE.

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