WDPN32 PGTW 170900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (PULASAN) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.4N 136.4E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 598 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 29 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD AND
ASYMMETRIC LOW-LEVEL CIRCULATION CENTER (LLCC) WITH CONVECTION
LOCATED TO THE EASTERN PERIPHERY OF THE SYSTEM, WHICH COMBINED WITH
A MAXIMUM WIND RADIUS OF 145NM IS CHARACTERISTIC OF A MONSOON
DEPRESSION. A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL TO THE
WEST IS THE PRIMARY SOURCE OF SUBSIDENT DRY AIR WHICH FULLY EXPOSES
THE LLCC. AN EARLIER 170336Z PARTIAL GCOM W1 AMSR2 IMAGE CONFIRMS
ELEVATED WIND SPEEDS ABOVE 40KTS 145NM FROM THE LLCC IN THE WESTERN
SEMICIRCLE OF TROPICAL STORM (TS) 15W. THE FURTHEST EXTENT OF 35KT
WINDS IS 260NM NORTHWEST OF CENTER. THE INITIAL POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED ANIMATED MSI
REVEALING THE LLCC SOUTH OF A VORTICITY MAXIMUM POSITIONED TO THE
NORTH. THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE AFOREMENTIONED AMSR2 IMAGERY AND
SUPPLEMENTED BY THE AGENCY FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: AMSR2 WIND SPEED DATA

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

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

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: THE STRUCTURAL DEFINITION OF TS 15W PERSISTS
AND CONTINUES TO CARRY THE CHARACTERISTICS OF A MONSOON DEPRESSION
GIVEN THE AFOREMENTIONED BROAD CIRCULATION WITH A BAND OF ENHANCED
WINDS DISPLACED 145NM-260NM FROM CENTER. WARNINGS CONTINUE DUE TO
THE POTENTIAL FOR TS 15W TO TRANSITION INTO A TROPICAL CYCLONE AND
POTENTIAL IMPACTS TO OKINAWA WITHIN 24-36 HOURS. THE TRACK IS
FORECASTED TO CONTINUE NORTHWESTWARD WHILE DRIVEN BY A STR TO THE
NORTH. THE CONSTRUCTIVE INTERFERENCE OF THE TUTT AND THE STR
ENHANCES THE TRACK SPEED OF TS 15W UNCHARACTERISTICALLY HIGHER THAN
MOST TROPICAL STORM TRACK SPEEDS. THE SYSTEM IS ANTICIPATED TO
TRACK SOUTH OF OKINAWA BETWEEN 24-36 HOURS, CONTINUING FORWARD AND
MAKING LANDFALL SHORTLY AFTER TAU 48. THE SYSTEM IS EXPECTED TO
MAINTAIN THE CURRENT INTENSITY OF 45KTS THROUGH THE NEXT 24 HOURS
BEFORE GRADUALLY WEAKENING AS THE SYSTEM STRUGGLES WITH DRY AIR AND
THE GRADIENT BETWEEN THE SYSTEM AND THE NORTHERN STR. THE ENHANCED
WINDS TO THE WEST WOULD SHIFT TO WRAP AROUND THE NORTHERN PERIPHERY
OF THE SYSTEM, POTENTIALLY PLACING OKINAWA WITHIN THE HIGHEST
RADIUS OF WINDS AT THAT TIME. GIVEN THE LARGE DISPLACEMENT BETWEEN
THE CENTER AND THE WIND RADII, ANY TRACK DEVIATIONS SOUTH MAY
RESULT IN LARGER IMPACTS TO OKINAWA.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN STRONG TRACK
AGREEMENT NORTHWESTWARD OVER THE COURSE OF THE NEXT 96 HOURS WITH A
CROSS-TRACK DISCREPANCY OF 130NM BY THE END OF THE FORECAST PERIOD.
THE INTENSITY GUIDANCE IS SLIGHTLY BROADER WITH TWO OUTLIERS, HWRF
AND HAFS-A, FORECASTING INTENSIFICATION WHILE ALL OTHER JTWC
MULTI-MODEL CONSENSUS MEMBERS PREDICT A GRADUAL WEAKENING. THIS IS
LIKELY ATTRIBUTED TO THE UNUSUAL NATURE OF THE MONSOON DEPRESSION
AND THE DRY AIR THAT CONTINUOUSLY FEEDS INTO THE SYSTEM THROUGH
LANDFALL. 

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