Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 12w Warning Nr 10//

From: SIU Weather Processor <[email-masked]>
Date: Fri, 17 Sep 2010 06:05:05 -0500

WDPN31 PGTW 170300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W WARNING NR 10//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 12W (FANAPI), LOCATED APPROXIMATELY 400 NM EAST-
SOUTHEAST OF TAIPEI, TAIWAN, HAS TRACKED NORTH-NORTHWESTWARD AT 04
KNOTS OVER THE PAST SIX HOURS. THE SUBTROPICAL RIDGE OVER CHINA HAS
BUILT RAPIDLY THROUGHOUT THE DAY, CAUSING THE CYCLONE TO TURN MORE
NORTHWESTWARD. THERE IS HIGH CONFIDENCE IN THE CURRENT POSITION
BASED ON ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND A HIGH-
RESOLUTION 162228Z MICROWAVE IMAGE. TY 12W HAS ALSO INTENSIFIED BY
20 KNOTS OVER THE PAST 12 HOURS DUE TO IMPROVED POLEWARD OUTFLOW
INTO THE PASSING MID-LATITUDE TROUGH. THE RECENT VISIBLE IMAGERY AND
AVAILABLE MICROWAVE IMAGES INDICATE WELL CONSOLIDATED CONVECTION AND
THE BEGINNING STAGES OF AN EYE. THEREFORE, THE CURRENT INTENSITY OF
75 KNOTS IS BASED ON THE STRONG CONVECTIVE SIGNATURE AND SUPPORTED
BY DVORAK ESTIMATES FROM KNES AND RJTD OF 4.5 AND PGTW OF 4.0.
CURRENTLY, ANIMATED WATER VAPOR IMAGERY DOES SHOW THAT THE POLEWARD
OUTFLOW HAS STARTED TO WANE AS THE TROUGH HAS LIFTED TO THE
NORTHEAST AND THE SYSTEM IS PASSING OVER AN AREA OF LOWER OCEAN HEAT
CONTENT.
 3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY AND TRACK SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. AS THE MID-LATITUDE SHORT-WAVE TROUGH HAS PROPAGATED
NORTHEASTWARD OF JAPAN, THE SUBTROPICAL STEERING RIDGE POSITIONED
NORTH OF THE SYSTEM IS BECOMING THE DOMINANT STEERING INFLUENCE.
THIS WILL ALLOW THE SYSTEM TO TRACK INCREASINGLY WESTWARD AND TO
ACCELERATE UP TO 8-10 KNOTS OVER THE NEXT DAY. FANAPI SHOULD
INTENSIFY TO A PEAK NEAR 90 KNOTS AROUND TAU 24 DUE TO A POCKET OF
ROBUST OCEAN HEAT CONTENT. HOWEVER, THE SYSTEM IS NOT EXPECTED TO
INTENSIFY FURTHER DUE TO INCREASING NORTHERLY VERTICAL WIND SHEAR
ASSOCIATED WITH THE BUILDING RIDGE AND A LOSS OF POLEWARD OUTFLOW.
THE AVAILABLE NUMERICAL GUIDANCE IS IN VERY TIGHT AGREEMENT, EVEN
WBAR, WHICH NOW ALSO TRACKS THE SYSTEM OVER CENTRAL TAIWAN.
   C. IN THE EXTENDED PERIOD, TY 12W IS EXPECTED TO WEAKEN AFTER
CROSSING TAIWAN BETWEEN TAU 48 AND TAU 72 BUT SHOULD MAINTAIN 55-60
KNOT INTENSITY AS IT CROSSES THE TAIWAN STRAIT. THE SYSTEM IS
FORECAST TO MAKE LANDFALL OVER MAINLAND CHINA AFTER TAU 72 AND WILL
DISSIPATE BY TAU 120.//

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
To unsubscribe from WX-TROPL send e-mail to [email-masked] with
"unsub wx-tropl" in the body of your message. For help with WX-TROPL
write to [email-masked]. For more information on tropical weather products, see the NHC Homepage at http://www.nhc.noaa.gov.