Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 15w (megi) Warning Nr 27//

From: SIU Weather Processor <[email-masked]>
Date: Tue, 19 Oct 2010 09:22:19 -0500

WDPN31 PGTW 191500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (MEGI) WARNING NR 27//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 15W (MEGI), LOCATED APPROXIMATELY 395 NM SOUTHEAST
OF HONG KONG, HAS TRACKED WEST-NORTHWESTWARD AT 05 KNOTS OVER THE
PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY SHOWS THE SYSTEM
HAS MAINTAINED AN EYE THAT HAS BECOME MORE RAGGED AND ENLARGED.
ADDITIONALLY, WATER VAPOR ANIMATION DEPICTS EXCELLENT RADIAL OUTFLOW,
ESPECIALLY ON THE POLEWARD SIDE. THE CURRENT POSITION AND INTENSITY
ARE BASED ON DVORAK EYE FIXES FROM PGTW, RJTD, AND KNES. THESE ARE
SUPPORTED BY A 191154Z SSMI-S IMAGE SHOWING A CLOSED MICROWAVE EYE.
UPPER LEVEL ANALYSIS INDICATES TY 15W IS APPROXIMATELY 5 DEGREES TO
THE SOUTH OF A RIDGE AXIS WITH A MESOCALE ANTICYCLONE DIRECTLY OVER
THE SYSTEM. IT IS CURRENTLY TRACKING ALONG THE SOUTHWEST PERIPHERY OF
A DEEP-LAYERED SUBTROPICAL RIDGE (STR)TO THE NORTHEAST. TYPHOON MEGI
HAS BEGUN TO DRIFT MORE POLEWARD IN RESPONSE TO A MID-LATITUDE TROUGH
THAT IS DIGGING SOUTHEASTWARD INTO EAST CENTRAL CHINA.
3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY, HOWEVER, THE TRACK HAS
BEEN ADJUSTED MORE POLEWARD.
   B. TY 15W IS EXPECTED TO TRACK MORE NORTH-NORTHWESTWARD AFTER
TAU 12 AS THE AFOREMENTIONED TROUGH DEEPENS AND DIGS FURTHER SOUTH.
ENVIRONMENTAL CONDITIONS WILL REMAIN FAVORABLE FOR A SLIGHT INCREASE
IN INTENSITY FROM TAU 36 TO 48. AFTER TAU 48, THE SYSTEM WILL TURN
MORE NORTHWESTWARD AS AN EXTENSION OF THE STR TO THE NORTH BUILDS.
THE AVAILABLE NUMERIC GUIDANCE ARE IN POOR AGREEMENT WITH JGSM AND
EGRR FAVORING A DRASTIC POLEWARD TUG TOWARDS TAIWAN AND ECMWF
FAVORING A MORE WESTWARD TRAJECTORY. THIS FORECAST IS TO THE LEFT OF
JTWC CONSENSUS WITH BIAS TOWARDS ECMWF. THIS SOLUTION STAYS WITH
CURRENT FORECAST PHILOSOPHY FAVORING A LESS INTENSE POLEWARD MOTION
ALTHOUGH THE OVERALL TREND HAS BEEN TO THE RIGHT AND POLEWARD OF THE
PREVIOUS FORECAST.
   C. AS THE STR RE-BUILDS NORTH NEAR TAU 48, TYPHOON MEGI IS
EXPECTED TO GRADUALLY WEAKEN DUE TO INCREASING VERTICAL WIND SHEAR,
AND EVEN MORE RAPIDLY AFTER MAKING LANDFALL NEAR HONG KONG BEFORE TAU
96.//

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