WDPN32 PGTW 252100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.9N 135.0E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 463 NM SOUTHEAST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS BANDS OF
DEEP CONVECTION WRAPPING IN TO AN OBSCURED LOW-LEVEL CIRCULATION
CENTER (LLCC) WITH A SLOT OF DRY AIR WRAPPING IN TO THE CENTER FROM
THE EAST. WATER VAPOR IMAGERY DEPICTS STRONG WESTWARD OUTFLOW
ENCOURAGED BY THE REMNANTS OF A TROPICAL UPPER-TROPOSPHERIC TROUGH
(TUTT) CELL. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON A 251730Z GPM GMI COLOR-PROCESSED 37GHZ IMAGE DEPICTS A
DISTINCT BANDING EYE. THE INITIAL INTENSITY OF 75 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON AN EARLIER ULTRA-HIGH RESOLUTION
METOP-B ASCAT IMAGE REVEALING MAXIMUM WIND SPEEDS BETWEEN 65-70KTS
AND IS SUPPLEMENTED BY THE AGENCY AND OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: THE SOUTHWESTERN PERIPHERY OF A
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS
   CIMSS SATCON: 76 KTS AT 251638Z
   CIMSS ADT: 69 KTS AT 251740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG WESTWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST TRACK IS SLOWER THAN IN
THE PREVIOUS WARNINGS BETWEEN TAU 24-72 AS TYPHOON (TY) 11W ROUNDS
THE SUBTROPICAL RIDGE. AS A RESULT, THE SYSTEM WILL START
EXTRATROPICAL TRANSITION LATER IN THE FORECAST AS IT ENTERS THE
BAROCLINIC ZONE AT A LATER TIME.

FORECAST DISCUSSION: TY 11W IS FORECAST TO TRACK WEST-NORTHWESTWARD
THROUGH TAU 48 AS THE SYSTEM APPROACHES THE AXIS OF THE STR TO THE
NORTHEAST. TRACK SPEED WILL INCREASE ONCE THE SYSTEM PASSES
NORTHWARD OF THE RIDGE AXIS. THE TRACK WILL REMAIN NORTHEASTWARD
AFTER TAU 72 THROUGH TAU 120. VERTICAL WIND SHEAR (VWS) WILL BE
MODERATE BETWEEN 10-15KTS ALLOWING FOR SLOW INTENSIFICATION FOR THE
FIRST 24 HOURS OF THE FORECAST WHILE OTHER ENVIRONMENTAL FEATURES
REMAIN FAVORABLE. A DROP IN VWS BETWEEN TAU 24-36 WILL ALLOW A
HIGHER RATE OF INTENSIFICATION TO A PEAK OF 110KTS BY TAU 36. TY
11W WILL START TO WEAKEN AS THE SYSTEM INTERACTS WITH THE
MOUNTAINOUS TERRAIN OF SOUTHERN JAPAN FROM TAU 72-120. INTERACTION
WITH AN UPPER-LEVEL TROUGH AT TAU 120 WILL CAUSE TY 11W TO BECOME
BAROCLINIC AND START EXTRATROPICAL TRANSITION.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT TY 11W WILL ROUND THE RIDGE AND PASS THE RIDGE AXIS BETWEEN
TAU 48-72 WITH A MINOR CROSS-TRACK SPREAD OF 140NM BY TAU 48. THE
ALONG-TRACK SPREAD AFTER TAU 72 OPENS SIGNIFICANTLY TO 820NM DUE TO
DRASTICALLY DIFFERENT TRACK SPEEDS REPRESENTED BY THE JTWC
CONSENSUS GUIDANCE. THE JTWC TRACK FORECAST IS SLIGHTLY FASTER THAN
THE MULTI-MODEL CONSENSUS. THE INTENSITY GUIDANCE IS ALSO IN STRONG
AGREEMENT THROUGH TAU 36 THAT VERTICAL WIND SHEAR WILL HINDER
INTENSIFICATION, BUT THE RATE OF INTENSIFICATION OPENS LARGELY BY
TAU 48 WITH A SPREAD OF 60KTS. HAFS-A AND GFS STAND OUT AS THE
STRONGEST MEMBERS WITH A PEAK OF 135 WHICH IS 25KTS ABOVE THE
MULTI-MODEL CONSENSUS. THE JTWC INTENSITY GUIDANCE LIES CLOSELY TO
THE MULTI-MODEL CONSENSUS MEAN.

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