WDPN31 PGTW 150900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (TALIM)         
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.0N 118.0E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 267 NM NORTHWEST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AFTER A SHORT 12-HOUR STALL EVIDENT IN THE 141351Z ASCAT-C AND
150129Z ASCAT-B IMAGES, TROPICAL STORM (TS) 04W HAS RESUMED A SLOW
NORTHWESTWARD TRACK. THIS STALL WAS LIKELY ASSOCIATED WITH THE
PASSAGE OF AN UPPER-LEVEL SHORTWAVE TROUGH TO THE NORTH, WHICH HAS
TEMPORARILY WEAKENED THE SUBTROPICAL STEERING RIDGE. BASED ON THE
150129Z ASCAT-B AND 150221Z ASCAT-C IMAGES, THE 150000Z WARNING
POSITION WAS RELOCATED ABOUT 84NM EAST-SOUTHEAST WITH NO
SIGNIFICANT CHANGE IN THE JTWC TRACK FORECAST. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) CONTINUES TO DEPICT A BROAD
LOW-LEVEL CIRCULATION CENTER (LLCC) WITH DEEP CONVECTIVE BANDING
PRIMARILY OVER THE WESTERN AND SOUTHERN SEMICIRCLES DUE TO
NORTHEASTERLY VERTICAL WIND SHEAR AT LOW TO MODERATE LEVELS. THIS
STRUCTURE IS ALSO EVIDENT IN THE 150505Z AMSR2 89GHZ AND 37GHZ
MICROWAVE IMAGES WHICH REVEAL DISORGANIZED, ISOLATED CORE
CONVECTION AND WEAK BANDING OVER THE NORTHERN SEMICIRCLE.
ENVIRONMENTAL CONDITIONS REMAIN GENERALLY FAVORABLE WITH STRONG
WESTWARD OUTFLOW, AIDED BY AN UPPER-LOW NEAR HAINAN ISLAND, AND
VIGOROUS EQUATORWARD OUTFLOW. POLEWARD OUTFLOW IS LIMITED DUE TO
CONVERGENT FLOW ALONG THE NORTHERN PERIPHERY OF THE SYSTEM. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
AFOREMENTIONED ASCAT IMAGES AND MSI. THE INITIAL INTENSITY OF 35
KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE ASCAT DATA AND
THE PGTW, KNES DVORAK ESTIMATES AS WELL AS THE UW-CIMSS ADT AND
AIDT ESTIMATES (33-37 KNOTS).

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WEAK EXTENSION OF THE LOW- TO MID-LEVEL
SUBTROPICAL RIDGE POSITIONED TO THE NORTH AND NORTHEAST WITH AN
UPPER-LEVEL SHORTWAVE TROUGH OVER EAST CENTRAL CHINA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 36 KTS AT 150558Z
   CIMSS ADT: 33 KTS AT 150530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   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 04W IS EXPECTED TO TRACK STEADILY
WEST-NORTHWESTWARD ALONG THE SOUTHWESTERN FLANK OF THE SUBTROPICAL
RIDGE, WHICH IS FORECAST TO RE-BUILD AS THE SHORTWAVE TROUGH FILLS 
AND PROPAGATES NORTHEASTWARD OVER THE NEXT 12 HOURS. ENVIRONMENTAL 
CONDITIONS ARE EXPECTED TO GRADUALLY IMPROVE WITH DECREASING 
NORTHEASTERLY VERTICAL WIND SHEAR AND IMPROVED POLEWARD OUTFLOW INTO 
THE SUBTROPICAL WESTERLIES OVER CENTRAL CHINA. THIS SHOULD ALLOW THE 
SYSTEM TIME TO RAPIDLY CONSOLIDATE AFTER TAU 12 WITH A HIGH 
PROBABILITY OF RAPID INTENSIFICATION PRIOR TO LANDFALL NEAR TAU 60. 
THUS THE PEAK OF 90 KNOTS IS EXPECTED IN THE TAU 48 TO TAU 60 WINDOW. 
AFTER TAU 60, TS 04W WILL WEAKEN SIGNIFICANTLY AS IT INTERACTS WITH 
HAINAN ISLAND AND SOUTHERN CHINA THEN QUICKLY CROSSES THE GULF OF 
TONKIN MAKING LANDFALL OVER VIETNAM NEAR TAU 72. THE SYSTEM WILL 
RAPIDLY DISSIPATE OVER NORTHERN VIETNAM THROUGH THE EXTENDED FORECAST 
PERIOD.       

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
THROUGH TAU 72 WITH A 135NM CROSS-TRACK SPREAD AT TAU 72. NAVGEM
AND ECMWF REMAIN ON THE SOUTHERN EDGE OF THE AIDS ENVELOPE WITH A
TRACK OVER NORTHERN HAINAN ISLAND WHILE THE BULK OF THE MODELS
INDICATE A MORE WEST-NORTHWESTWARD TRACK OVER OR TO THE NORTH OF
THE LEIZHOU PENINSULA. AFTER TAU 72, NUMERICAL MODEL GUIDANCE 
DIVERGES DUE TO THE WEAKENING LOW-LEVEL VORTEX. THE 150000Z COAMPS-TC 
ENSEMBLE CONTINUES TO INDICATE A PEAK RAPID INTENSIFICATION 
PROBABILITY OF 80 PERCENT IN THE TAU 24 TO TAU 54 PERIOD.    

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: HIGH//
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