WDPN32 PGTW 190300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (PULASAN) WARNING NR 
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.7N 126.1E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 323 NM SOUTHWEST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 23 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS 15W
(PULASAN) WITH A FEATURES MORE CONSISTENT WITH A TROPICAL CYCLONE
VICE A MONSOON DEPRESSION. THE LOW-LEVEL CIRCULATION CENTER (LLCC)
HAS CONTINUED TO CONSOLIDATE WITH PERSISTENT CONVECTION OVER THE
CENTER. ENVIRONMENTAL ANALYSIS INDICATES THAT 15W IS CURRENTLY IN A
MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE OUTFLOW
ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA
SURFACE TEMPERATURES OFFSET BY DRY AIR ENTRAINMENT. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED MSI
SHOWING THE CONSOLIDATING LLCC. THE INITIAL INTENSITY OF 40 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE HIGH END OF INTENSITY 
ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T1.5 - 25 KTS
   CIMSS ADT: 37 KTS AT 190030Z
   CIMSS AIDT: 38 KTS AT 190030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT ALONG THE SOUTHWESTERN
QUADRANT.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: 15W IS FORECAST TO CONTINUE TRACKING
NORTHWESTWARD ALONG THE PERIPHERY OF THE STR TO THE NORTHEAST
THROUGH TAU 24. NEAR TAU 24, 15W IS ANTICIPATED TO MAKE LANDFALL
NEAR SHANGHAI AND A TROUGH THAT BEGINS TO BREAK DOWN AN EXTENSION
OF THE RIDGE CREATES A WEAK STEERING ENVIRONMENT CAUSING VERY SLOW
TRACK SPEEDS AROUND THAT TIME. AT TAU 36, 15W IS FORECAST TO THEN
START AN EAST-NORTHEASTWARD TRACK AS THE RIDGE TAKES OVER AS THE
PRIMARY STEERING INFLUENCE ONCE AGAIN. AROUND TAU 48, TRACK SPEEDS
ARE EXPECTED TO GREATLY INCREASE DUE TO INTERACTION WITH THE JET
MARKING THE BEGINNING OF EXTRATROPICAL TRANSITION. THE SYSTEM WILL
THEN TRACK BRISKLY ALONG THE SOUTHERN COAST OF SOUTH KOREA IN THE
KOREA STRAIT AND INTO THE SEA OF JAPAN. AS A RESULT OF THE
BAROCLINIC ZONE BEING PUSHED SOUTH BY THE TROUGH, 15W IS FORECAST
TO QUICKLY COMPLETE EXTRATROPICAL TRANSITION NEAR TAU 72. REGARDING
INTENSITY, 15W IS EXPECTED TO GRADUALLY WEAKEN AS IT HEADS TOWARD
SHANGHAI WHERE IT MAKES LANDFALL AS A BORDERLINE TROPICAL STORM.
ONCE THE SYSTEM MAKES IT BACK OUT OVER WATER, A STEADY
INTENSIFICATION TREND WILL ENSUE, HOWEVER STRONG VERTICAL WIND
SHEAR WILL CAP THE INTENSITY TO A PEAK OF 40 KTS. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN BETTER AGREEMENT
WITH A LARGER BULK OF GUIDANCE SHOWING THE SHARP TURN BACK OVER
WATER RATHER THAN DISSIPATION OVER EASTERN CHINA. AFTER TAU 36,
MODELS VARY IN THE SHARPNESS OF THE TURN WITH HWRF AND HAFS-A BOTH
TRACKING THE VORTEX THROUGH SOUTHERN SOUTH KOREA WHILE GFS AND ITS
ENSEMBLE MEAN A BIT FURTHER SOUTH, OFF THE COAST OF SOUTH KOREA.
THE JTWC TRACK FORECAST IS PLACED WITH OVERALL LOW CONFIDENCE DUE
TO THE CONTINUED POSSIBILITY OF DISSIPATION IN EASTERN CHINA.
INTENSITY GUIDANCE IS IN MODERATE AGREEMENT WITH SOME VARIANCE DUE
TO TRACK DIFFERENCES AND TIME OVER LAND. THE JTWC INTENSITY
FORECAST IS PLACED CLOSE TO CONSENSUS WITH LOW CONFIDENCE AS WELL
FOR SIMILAR REASONS.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   INTENSITY 0 - 72 HR: LOW//
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