Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Storm 11w Warning Nr 03//

From: SIU Weather Processor <[email-masked]>
Date: Wed, 8 Sep 2010 09:02:16 -0500

WDPN31 PGTW 081500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W WARNING NR 03//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 11W (ELEVEN), LOCATED APPROXIMATELY 305 NM
EAST-SOUTHEAST OF HONG KONG, HAS TRACKED WESTWARD AT 08 KNOTS OVER
THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY INDICATES
A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH DEEP
CONVECTIVE BANDING PRIMARILY OVER THE SOUTHERN SEMI-CIRCLE. ANIMATED
WATER VAPOR IMAGERY INDICATES THAT THE TUTT CELL, WHICH HAD PROVIDED
IMPROVED POLEWARD (EASTWARD) OUTFLOW, HAS TRACKED WEST OVER TAIWAN
AND IS PRODUCING WEAK TO MODERATE (10-15 KNOT) NORTHERLY VERTICAL
WIND SHEAR (VWS). A 080849Z SSMIS COMPOSITE IMAGE AND A 081059Z
AMSU IMAGE SHOW CURVED BANDING WRAPPING INTO THE EXPOSED LLCC,
WHICH IS LOCATED ON THE NORTHERN EDGE OF THE DEEP CONVECTION. RADAR
IMAGERY ALSO SUPPORTS THE CURRENT POSITION WITH GOOD CONFIDENCE.
THE CURRENT INTENSITY IS BASED ON DVORAK ESTIMATES OF 35 KNOTS
FROM BOTH PGTW AND KNES AS WELL AS AN EARLIER 080211Z ASCAT IMAGE
SHOWING NUMEROUS 30-35 KNOT WIND VECTORS AROUND THE CENTER.
3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 11W IS TRACKING WESTWARD UNDER THE STEERING INFLUENCE OF
THE LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR), WHICH EXTENDS WESTWARD
ALONG 28-30N LATITUDE INTO EASTERN CHINA FROM A HIGH CENTERED NEAR
27N 140E. GFS IS INDICATING A SHARP TURN NORTHWARD AFTER TAU
12. MODEL FIELDS INDICATE GFS IS WEAKENING THE SYSTEM TOO RAPIDLY AND
IS LOSING THE CIRCULATION COMPLETELY BY TAU 36. NOGAPS IS TURNING
THE SYSTEM SHARPLY NORTHWARD AFTER TAU 24 AND ALSO WEAKENS THE
SYSTEM TOO RAPIDLY. NOGAPS/GFS ARE INITIALIZING THE STR WELL BUT
APPEAR TO BE WEAKENING THE STR TOO RAPIDLY, DRIVING THE SYSTEM
DIRECTLY INTO THE EXISTING STR. THIS HAS BEEN A CONTINUING PROBLEM
OVER THE PAST 24 HOURS. THE REMAINING MODELS (ECMWF, JGSM, GFDN AND
WBAR) ARE IN GOOD AGREEMENT AND INDICATE A NORTHWESTWARD TRACK THAT
MAKES SENSE WITH THE LATEST 500/700MB ANALYSIS OF THE STR. TS 11W IS
EXPECTED TO STRENGTHEN TO A PEAK INTENSITY OF 40 TO 45 KNOTS BY TAU
24 AS THE TUTT CELL WEAKENS AND NORTHERLY VWS DECREASES. THE SYSTEM
IS FORECAST TO MAKE LANDFALL BY TAU 36 AND WILL DISSIPATE BY TAU 48.
THE FORECAST TRACK IS FASTER THAN THE MODEL CONSENSUS AND LEFT OF
CONSENSUS DUE TO THE AFOREMENTIONED NOGAPS/GFS POLEWARD BIAS.//

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