WDPN32 PGTW 170300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (PULASAN) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.5N 138.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 771 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 19 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN
ILL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC), WITH A DIFFUSE AND
BROAD REGION OF LOW WIND SPEEDS CHARACTERISTIC OF A MONSOON
DEPRESSION. THE SYSTEM REMAINS ASYMMETRIC, WITH DEEP CONVECTION
CONFINED ON THE EASTERN SIDE OF THE CIRCULATION DUE TO CONTINUING
WESTERLY VERTICAL SHEAR OF 20-25 KT. THE MAXIMUM WIND BAND
CONTINUES TO EXTEND MORE THAN 200 NM FROM THE LLCC IN THE EASTERN
SEMICIRCLE. THE OVERALL STRUCTURE HAS NOT CHANGED SIGNIFICANTLY,
AND THE INITIAL INTENSITY REMAINS SET AT 35 KT. UPPER-LEVEL OUTFLOW
REMAINS RESTRICTED TO THE EAST AND SOUTH.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE OVER JAPAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RCTP: T1.5 - 25 KTS
   KNES: T1.0 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DEEP-LAYER DRY AIR MASS TO THE WEST AND NORTHWEST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: 15W (PULASAN) IS ASSESSED TO BE A MONSOON
DEPRESSION WITH A CHARACTERISTICALLY BROAD CIRCULATION STRUCTURE,
CONSISTING OF A MAX WIND BAND LOCATED 130 TO 230 NM EAST OF THE
CENTER. DUE TO THE POTENTIAL FOR TRANSITION INTO A TROPICAL CYCLONE
AND IMPACTS TO OKINAWA WITHIN 36 HOURS, WARNINGS ARE BEING ISSUED
ON 15W (PULASAN). THE STORM'S FORWARD HEADING CONTINUES TO BE
SOMEWHAT ERRATIC DUE TO ITS BROAD NATURE, BUT THE OVERALL 12-HOUR
MEAN MOTION IS NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE
SUBTROPICAL RIDGE OVER JAPAN. THE TRACK FORECAST PHILOSOPHY IS
STRAIGHT-FORWARD AND UNCHANGED FROM THE PREVIOUS WARNING, AS THIS
SAME RIDGE SHOULD DIRECT PULASAN BRISKLY NORTHWESTWARD INTO THE
EAST CHINA SEA IN 36 TO 48 HOURS. SOME TRACK ADJUSTMENTS ARE
POSSIBLE IF THE BROAD VORTEX RECONSOLIDATES AROUND A DIFFERENT
LOCATION DUE TO THE INFLUENCE OF DEEP CONVECTION. THE JTWC TRACK
FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS AND PASSES WITHIN 30 
NM SOUTH OF OKINAWA IN ABOUT 36 HOURS. INTENSIFICATION, IF ANY IS 
EXPECTED TO BE LIMITED DURING THIS TIME DUE TO WIND SHEAR AND DRY AIR 
ASSOCIATED WITH AN UPPER-LEVEL LOW TO THE STORM'S NORTHWEST. SHEAR 
VALUES MAY DECREASE AFTER 12 TO 24 HOURS, BUT EXTENSIVE DRY 
ENTRAINMENT COULD PREVENT THE FORMATION OF A COMPACT INNER CORE 
DESPITE LOWER SHEAR. MOST MODELS AGREE ON THIS EVOLUTION, BUT IF A 
COMPACT INNER CORE DOES FORM, PULASAN'S INTENSITY COULD BE HIGHER. 
THE MAX WIND BAND IS EXPECTED TO GRADUALLY ROTATE FROM THE EASTERN 
SIDE OF THE CIRCULATION TO THE NORTHERN SIDE AS PULASAN APPROACHES 
OKINAWA. IT SHOULD BE STRESSED THAT THE CPA VALUE MAY DO A POORER JOB 
THAN USUAL OF CONVEYING RISK IN THIS CASE, AS THE STRONGEST WINDS 
COULD REMAIN ANOMALOUSLY FAR FROM THE CENTER BASED ON CURRENT MODEL
GUIDANCE. 15W'S INTENSITY IS EXPECTED TO GRADUALLY DECREASE AFTER
24 HOURS DUE TO A SLACKENING GRADIENT BETWEEN THE STORM AND THE
SUBTROPICAL RIDGE OVER JAPAN, BUT SHOULD A COMPACT CONVECTIVE INNER
CORE DEVELOP, THE INTENSITY WOULD LIKELY BE A BIT HIGHER THAN
FORECAST. AFTER 36 HOURS, A TRACK THROUGH THE EAST CHINA SEA IS
EXPECTED TO CARRY 15W INTO MAINLAND CHINA BY 72 HOURS, WHERE IT
WOULD QUICKLY DISSIPATE INLAND.

MODEL DISCUSSION: DYNAMICAL MODEL TRACK GUIDANCE REMAINS CLOSELY
CLUSTERED, AND THE JTWC FORECAST IS CLOSE TO THE MULTI-MODEL
CONSENSUS WITH HIGH CONFIDENCE THROUGH 72 HOURS. THE JTWC INTENSITY
FORECAST REMAINS CLOSE TO A BLEND OF THE GFS, ECMWF, AND HAFS-A
WITH AVERAGE CONFIDENCE.

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