WDPN32 PGTW 192100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (PULASAN) 
WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.9N 121.4E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 19 NM SOUTH-SOUTHWEST OF SHANGHAI, CHINA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION 15W (PULASAN) WITH A COMPACT CORE OF CONVECTION OVER
LAND NEAR SHANGHAI. THERE IS ALSO ANOTHER LOW-LEVEL CIRCULATION
(LLC) THAT IS JUTTING OUT FROM UNDER THE CONVECTION, WHICH MAY
CAUSE A JUMP IN THE TRACK IF THE SYSTEM CONSOLIDATES AROUND THAT
CIRCULATION. THE STRONGEST WINDS CONTINUE TO BE DISPLACED ABOUT 80
NM TO THE NORTHEAST WITH SLIGHTLY WEAKER WINDS NEAR THE CENTER.
ENVIRONMENTAL ANALYSIS INDICATES THAT 15W IS IN A MARGINAL
ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD OUTFLOW ALOFT AND LOW
(5-10 KTS) VERTICAL WIND SHEAR OFFSET BY THE TERRAIN INTERACTION
WITH EASTERN CHINA. THE INITIAL POSITION IS PLACED WITH LOW
CONFIDENCE BASED ON THE ANIMATED EIR AND RADAR IMAGERY. THE
POSSIBILITY OF THE MENTIONED LLC BEING THE MAIN CENTER RATHER THAN
CLOSER TO THE CONVECTION IS THE CAUSE FOR THE LOWER POSITIONING
CERTAINTY. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE SUBJECTIVE AND OBJECTIVE INTENSITY
ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T1.5 - 25 KTS
   RCTP: T2.0 - 30 KTS
   DEMS: T1.5 - 25 KTS
   CIMSS DPRINT: 32 KTS AT 191800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: OVER LAND
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: TERRAIN INTERACTION

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: 15W IS FORECAST TO TRACK NORTHWESTWARD OVER
THE NEXT 12 HOURS. NEAR TAU 12, THE RIDGE EXTENSION THAT IS
CURRENTLY STEERING THE SYSTEM IS FORECAST TO BREAK DOWN AND THE
STEERING PATTERN WILL QUICKLY SHIFT AS THE RIDGE REORIENTS. AFTER
REORIENTATION, THE STR IS EXPECTED TO PULL 15W NORTHEASTWARD AS IT
ROUNDS THE RIDGE. 15W IS THEN EXPECTED TO BRISKLY TRAVERSE
THROUGH THE KOREA STRAIT, ALONG THE COAST OF SOUTHERN KOREA AND
INTO THE SEA OF JAPAN. EXTRATROPICAL TRANSITION IS FORECAST TO
BEGIN NEAR TAU 36 AS IT STARTS TO INTERACT WITH THE JET AND THE
BAROCLINIC ZONE WITH COMPLETION BY TAU 48. REGARDING INTENSITY, 15W
IS FORECAST TO MAINTAIN INTENSITY AS IT SKIRTS ALONG EASTERN CHINA.
AFTER REENTRY OVER WATER THE SYSTEM IS EXPECTED TO SLIGHTLY
INTENSIFY TO A PEAK OF 40 KTS NEAR TAU 36, JUST BEFORE IT INTERACTS
WITH THE COAST OF SOUTH KOREA. THE INTENSITY WILL BE CAPPED BY THE
HIGH SHEAR IN THE AREA DUE TO THE JET BEING LOWERED BY AN
APPROACHING TROUGH. AROUND TAU 48, 15W WILL TRANSITION TO AN
EXTRATROPICAL LOW AS IT SHOOTS OFF TO THE EAST-NORTHEAST. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN MUCH BETTER
AGREEMENT ON THE EASTWARD TURN AFTER TAU 12 WITH A TIGHT SPREAD
BETWEEN CONSENSUS MEMBERS. WITH THE EXCEPTION OF THE ECMWF
ENSEMBLE, WHICH SUGGESTS A SHARPER TURN ALMOST DIRECTLY EASTWARD,
THERE IS A 45 NM CROSS-TRACK SPREAD AT TAU 36. HOWEVER, IF A JUMP
IN POSITION FOR THE NEXT WARNING OCCURS, THE TRACK COULD BE ALTERED
IN RESPONSE. AS A RESULT, THE JTWC TRACK FORECAST IS PLACED WITH
ONLY MEDIUM CONFIDENCE TO ACCOUNT FOR THE POSITIONAL UNCERTAINTY.
INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT WITH MEMBERS SHOWING A
SLIGHT INTENSIFICATION TREND AFTER TAU 12 TO A PEAK OF 40-45 KTS AT
TAU 36. THE JTWC INTENSITY FORECAST IS PLACED WITH MEDIUM
CONFIDENCE TO ACCOUNT FOR THE POSSIBLE TRACK JUMP AS WELL. 

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