WDPN32 PGTW 182100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (PULASAN) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.0N 127.8E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 30 NM NORTH OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS 15W
(PULASAN) WITH A LOW-LEVEL CIRCULATION CENTER (LLCC) THAT IS
SEEMINGLY BEGINNING TO CONSOLIDATE WITH MUCH TIGHTER WRAPPING ALONG
THE SOUTHWESTERN QUADRANT. CENTRAL CONVECTION HAS RECENTLY STARTED
TO FORM OVER THE CIRCULATION CENTER AS WELL. NONETHELESS, THE
STRONGER WINDS STILL REMAIN DISPLACED ABOUT 100 NM IN NORTHEASTERN
AND NORTHERN PERIPHERIES OF THE SYSTEM WITH WEAKER WINDS NEAR THE
CENTER CHARACTERISTIC OF A MONSOON DEPRESSION. ENVIRONMENTAL
ANALYSIS INDICATES THAT 15W IS IN A MARGINALLY FAVORABLE
ENVIRONMENT CHARACTERIZED BY WEAK OUTFLOW ALOFT, LOW VERTICAL WIND
SHEAR (5-10 KTS), DRY AIR PRESENT IN THE SOUTHWESTERN QUADRANT, AND
WARM (30-31 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED EIR IMAGERY.
THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON PERSISTENCE FROM A COMBINATION OF A 181314Z ASCAT-C IMAGE
SHOWING 40 KTS ON THE EDGE OF THE SWATH, NORTH OF OKINAWA, AND A
181535Z OSCAT IMAGE SHOWING A MAX OF 40 KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) POSITIONED TO
THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: WEAK POLEWARD AND EQUATORWARD
   OTHER FACTORS: PRESENCE OF DRY AIR IN THE SOUTHWESTERN
PERIPHERY.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: TRACK WAS SIGNIFICANTLY CHANGED AND
LENGTHENED DUE TO VORTEX TRACKERS CONTINUING TO SHOW A MORE BRIEF
LANDFALL AND A TURN BACK OVER WATER EAST OF SHANGHAI WITH SLIGHT
INTENSIFICATION.

FORECAST DISCUSSION: 15W IS FORECAST TO CONTINUE TRACKING
NORTHWESTWARD OVER THE NEXT 36 HOURS WITH LANDFALL OCCURRING BETWEEN
TAUS 24 AND 36, SOUTH OF SHANGHAI. AFTER TAU 36 A TROUGH BEGINS TO
BREAK DOWN THE RIDGE AND CAUSES A WEAK STEERING ENVIRONMENT THROUGH
TAU 48. AFTER TAU 48, THE WESTERN PERIPHERY OF THE STR WILL BECOME
THE PRIMARY STEERING MECHANISM AND DRIVE THE SYSTEM
EAST-NORTHEASTWARD FOR THE REMAINDER OF THE FORECAST PERIOD.
BETWEEN TAU 72 AND 96 15W IS FORECAST TO TRACK THROUGH THE KOREA
STRAIGHT WITH A SECOND LANDFALL WEST OF IWAKUNI. EXTRATROPICAL
TRANSITION IS EXPECTED TO BEGIN NEAR AROUND TAU 72 WITH COMPLETION
NEAR TAU 96 AS IT BEGINS TO INTERACT WITH THE JET AND BAROCLINIC
ZONE THAT IS PUSHED FURTHER SOUTH DUE TO THE TROUGHING. REGARDING
INTENSITY, 15W IS FORECAST TO GRADUALLY WEAKEN TO AROUND 35 KTS
JUST BEFORE LANDFALL NEAR SHANGHAI AND THEN WEAKEN TO 25 KTS AS IT
REMAINS OVER LAND. NEAR TAU 48, AS 15W BEGINS TO BE PICKED UP BY
THE STR AND PULLED BACK OVER WATER, A BRIEF INTENSIFICATION PHASE
WILL ENSUE. THIS WILL BE CAPPED BY THE VERY HIGH SHEAR THAT WILL BE
ACTING ON THE SYSTEM AT TAU 72. THEREFORE, A PEAK OF 40 KTS IS
FORECAST BEFORE THE SYSTEM MAKES ITS FINAL LANDFALL AND BEGINS TO
QUICKLY DUE TO LAND INTERACTION.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN POOR AGREEMENT
AFTER TAU 36 WITH SOME MODELS HAVING THE SYSTEM DISSIPATE OVER
EASTERN CHINA, HOWEVER THE BULK OF GUIDANCE DEPICTS THE
REINTENSIFICATION OVER WATER SCENARIO. THE GEFS AND ECENS ENSEMBLES
ALSO DIVERGE WITH MEMBERS SPLIT BETWEEN THE TWO SCENARIOS. THE JTWC
TRACK FORECAST IS PLACED WITH LOW CONFIDENCE AND FOLLOWS MORE
CLOSELY TO THE CONSENSUS AS THE ENVIRONMENT AND STEERING PATTERN
SEEM CONDUCIVE FOR THAT TYPE OF TRACK. THE SECOND LANDFALL IS
VARIED BETWEEN MODELS WITH HWRF MAKING LANDFALL ALONG THE SOUTHERN
COAST OF KOREA AND THE GFS TRACKS THE VORTEX CLOSER TO SASEBO.
INTENSITY GUIDANCE IS ALSO IN POOR AGREEMENT DUE TO THE HIGH
VARIANCE IN TRACKS. HWRF IS THE MOST AGGRESSIVE WITH A PEAK OF
AROUND 65 KTS BEFORE MAKING LANDFALL IN SOUTH KOREA. THE REMAINDER
OF GUIDANCE SUGGESTS A MORE MELLOW INTENSIFICATION AND THE JTWC
INTENSITY FORECAST FOLLOWS MORE CLOSELY TO THAT DUE TO THE VERY
HIGH SHEAR IN THE AREA.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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