WDPN32 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (PULASAN) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.2N 134.7E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 494 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A BROAD
MONSOON DEPRESSION WITH SUBSIDENT DRY AIR REVEALING THE LOW-LEVEL
CIRCULATION CENTER (LLCC). A BAND OF ENHANCED WIND WRAPS AROUND THE
EASTERN PERIPHERY OF TROPICAL STORM (TS) 15W WITH ASSOCIATED DEEP
CONVECTION WHILE THE CENTER REMAINS CLEAR AND FED WITH DRY AIR FROM
THE TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL LOCATED TO THE
WEST.  THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED
ON THE ANIMATED EIR DEPICTING A BROAD AREA OF TURNING AND A CLEAR
CENTER OF DRY AIR, MAKING PINNING DOWN A CENTER LOCATION DIFFICULT.
WHILE FNMOC IS EXPERIENCING A SYSTEM DEGRADATION, DATA FOR TS 15W
HAS BEEN SPARSE UNTIL A 170857Z RCM-2 SYNTHETIC APERTURE RADAR
(SAR) PASS REVEALED MUCH STRONGER WINDS (60-70KTS) THAN ASSESSED IN
THE PREVIOUS WARNING. THE ELEVATED INTENSITY WAS FURTHER SUPPORTED
BY A SIMILARLY TIMED 170911Z SMOS PASS DISCLOSING DATA ABOVE 55KTS,
NAILING DOWN THE INTENSITY ASSESSMENT TO BE 60KTS. NEVERTHELESS,
BOTH IMAGES WERE PARTIAL PASSES DUE TO THE LARGE DIAMETER OF THE
SYSTEM WITH A MAXIMUM 35KT WIND RADIUS OF 310NM. THE INITIAL
INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AFOREMENTIONED SMOS AND SAR PARTIAL IMAGERY AND THE INABILITY TO
CAPTURE THE INTENSITY THROUGHOUT THE ENTIRE SYSTEM.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: 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: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE INTENSITY FORECAST HAS CHANGED
SIGNIFICANTLY SINCE THE PREVIOUS WARNING DUE TO UPDATED WIND SPEED
DATA FROM RCM-2 AT 170857Z THAT INDICATES WIND SPEEDS UP TO 60KTS
IN THE NORTHERN AND EASTERN PERIPHERY OF THE SYSTEM. AS A RESULT,
THE OVERALL TRACK INTENSITY IS HIGHER UNTIL LANDFALL, WHEN RAPID
WEAKENING WILL OCCUR. SINCE THE CURRENT INTENSITY IS HIGHEST IN THE
NORTHERN AND NORTHWESTERN PERIPHERY OF THE SYSTEM, THE IMPACTS TO
OKINAWA MAY BE GREATER THAN IN THE PREVIOUS WARNING AS THE SYSTEM
TRACKS SOUTH OF THE ISLAND.

FORECAST DISCUSSION: TS 15W CONTINUES TO MAINTAIN THE
CHARACTERISTICS OF A MONSOON DEPRESSION GIVEN THE AFOREMENTIONED
BROAD CIRCULATION AND ENHANCED WINDS DISPLACED 145NM-310NM FROM
CENTER. WARNINGS CONTINUE DUE TO THE POTENTIAL IMPACTS TS 15W MAY
BRING TO OKINAWA WITHIN 24 HOURS. TS 15W IS FORECAST TO TRACK
NORTHWESTWARD WHILE DRIVEN BY A STR TO THE NORTH. THE TRACK SPEED
IS EXPECTED TO BE ENHANCED ABOVE THE TYPICAL NATURE FOR A TROPICAL
SYSTEM DUE TO CONSTRUCTIVE INTERFERENCE BETWEEN THE STR AND A TUTT
CELL TO THE WEST DRIVING THE SYSTEM FORWARD. THE SYSTEM IS EXPECTED
TO TRACK APPROXIMATELY 50NM SOUTH OF OKINAWA WITHIN 24 HOURS, BUT
GIVEN THE LARGE NATURE OF THE MONSOON DEPRESSION THE WIND FIELD
WILL BE DISPLACED FAR FROM CENTER AND IS MORE LIKELY TO IMPACT
OKINAWA WHILE PASSING SOUTH. GIVEN THE CURRENT 145NM RADIUS OF
MAXIMUM WIND, IF THE SYSTEM WERE TO DEVIATE FARTHER SOUTH, THE
INTENSITY MAY INCREASE. THROUGH THE FIRST 48 HOURS, THE SYSTEM WILL
GRADUALLY WEAKEN UNTIL MAKING LANDFALL. THE PRESSURE GRADIENT
BETWEEN THE STR TO THE NORTH AND THE MONSOON DEPRESSION WILL
DIMINISH, INITIATING THE PROGRESSIVE WEAKENING TREND. THE WEAKENING
WILL FURTHER AS THE TUTT CELL CONTINUES TO FEED CONTINENTAL DRY AIR
INTO THE SYSTEM AND VERTICAL WIND SHEAR INCREASES, WEARING AWAY AT
CONVECTIVE DEVELOPMENT. ONCE MAKING LANDFALL, THE SYSTEM WILL
RAPIDLY WEAKEN TO DISSIPATION BY TAU 96 DUE TO TOPOGRAPHIC
INTERACTION. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN TIGHT
AGREEMENT AS THE SYSTEM TRACKS NORTHWESTWARD WITH A MAXIMUM
CROSS-TRACK SPREAD OF 100NM BY TAU 72, AND BIFURCATING VARIABLY BY
TAU 96 DUE TO RAPID WEAKENING AND DIFFICULTY FOR THE MODELS TO
TRACK THE WEAK AND ALREADY BROAD SYSTEM. THE INTENSITY GUIDANCE IS
UNRELIABLE GIVEN THE DIFFICULTY IN TRACKING THE CORE OF THE SYSTEM
AND THE DISLOCATED CIRCULATION CENTER. HAFS-A FORECASTS
INTENSIFICATION JUST ABOVE 60KTS FOR THE FIRST 36 HOURS WHILE HWRF
INDICATES RAPID WEAKENING WITH SPURIOUS INTENSIFICATION AT TAU 36
BEFORE MEETING THE SAME TREND OF WEAKENING AS HAFS-A. 

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