Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 12w Warning Nr 08//

From: SIU Weather Processor <[email-masked]>
Date: Thu, 16 Sep 2010 09:14:05 -0500

WDPN31 PGTW 161500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W WARNING NR 08//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 12W (FANAPI), LOCATED APPROXIMATELY 270 NM SOUTH
OF OKINAWA, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT 03 KNOTS OVER
THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY AND A 161145Z
SSMIS IMAGE DEPICT A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER
(LLCC) WITH A MICROWAVE EYE FEATURE AND IMPROVED CONVECTIVE BANDING
OVER THE EASTERN SEMI-CIRCLE. ANIMATED WATER VAPOR IMAGERY SHOWS
IMPROVED POLEWARD OUTFLOW ASSOCIATED WITH A MIDLATITUDE SHORT-WAVE
TROUGH PROPAGATING EASTWARD INTO CENTRAL JAPAN. BASED ON SEVERAL HIGH
RESOLUTION MICROWAVE IMAGES (160707Z TRMM, 160956Z SSMIS AND 161145Z
SSMIS), TY 12W IS SLOWING AND TURNING NORTHWARD TO NORTHWESTWARD.
RECENT INFRARED IMAGERY SUGGESTS THAT THE SYSTEM MAY EVEN BE
BEGINNING TO TRACK WEST-NORTHWESTWARD AS ANTICIPATED. THERE IS GOOD
CONFIDENCE IN THE CURRENT POSITION BASED ON THE WELL-DEFINED LLCC IN
THE 161145Z SSMIS IMAGE. THE SYSTEM HAS BEEN UPGRADED TO TYPHOON
STRENGTH (65 KNOTS) BASED ON DVORAK ESTIMATES OF 65 KNOTS FROM PGTW
AND RJTD, AND ON THE MUCH IMPROVED SATELLITE SIGNATURE.
3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY AND TRACK SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. THE 16/00Z 500MB ANALYSIS AS WELL AS RECENT SATELLITE IMAGERY
INDICATE THAT THE SUBTROPICAL RIDGE IS RAPIDLY BUILDING ACROSS THE
EAST CHINA SEA. THE MIDLATITUDE SHORT-WAVE TROUGH, WHICH HAD A
SHORT-TERM INFLUENCE ON THE TRACK IS PROPAGATING NORTHEASTWARD INTO
CENTRAL JAPAN. THEREFORE, THE SUBTROPICAL STEERING RIDGE POSITIONED
NORTH OF THE SYSTEM IS EXPECTED TO BECOME THE DOMINANT STEERING
INFLUENCE OVER THE NEXT 12-24 HOURS. THIS WILL ALLOW THE SYSTEM
TO TRACK WESTWARD AND TO ACCELERATE UP TO 8-10 KNOTS. TY 12W IS
EXPECTED TO MAKE LANDFALL OVER TAIWAN PRIOR TO TAU 72. FANAPI
SHOULD CONTINUE TO INTENSIFY AT A 15-20 KNOT PER DAY RATE BUT IS
EXPECTED TO PEAK AT 90 KNOTS BETWEEN TAU 36 AND 48 DUE TO INCREASING
NORTHERLY VERTICAL WIND SHEAR ASSOCIATED WITH THE BUILDING RIDGE.
THE AVAILABLE NUMERICAL GUIDANCE IS IN TIGHT AGREEMENT WITH THE
EXCEPTION OF WBAR, WHICH IS THE ONLY MODEL INDICATING A TRACK
NORTH OF TAIWAN (REMAINS THE ONLY OUTLIER). ALL THE OTHER MODELS
TRACK THE SYSTEM OVER TAIWAN.
   C. IN THE EXTENDED PERIOD, TY 12W IS EXPECTED TO WEAKEN AFTER
CROSSING TAIWAN BUT SHOULD MAINTAIN 55-60 KNOT INTENSITY AS IT
CROSSES THE TAIWAN STRAIT. THE SYSTEM IS FORECAST TO MAKE LANDFALL
OVER MAINLAND CHINA BY TAU 96 AND SHOULD DISSIPATE BY TAU 120.//

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