Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 15w (megi) Warning Nr 31//

From: SIU Weather Processor <[email-masked]>
Date: Wed, 20 Oct 2010 08:48:05 -0500

WDPN31 PGTW 201500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (MEGI) WARNING NR 31//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 15W (MEGI), LOCATED APPROXIMATELY 285 NM SOUTH-
EAST OF HONG KONG, CHINA HAS TRACKED NORTHWARD AT 07 KNOTS OVER THE
PAST SIX HOURS. ANIMATED WATER VAPOR IMAGERY SHOWS THE SYSTEM HAS
BEGUN TO ERODE ALONG ITS NORTHERN PERIPHERY AS IT GETS EXPOSED TO THE
STRONG UPPER LEVEL WESTERLY WINDS. THERE IS ALSO A NOTED DECREASE IN
THE DEEP CONVECTION ALONG THE NORTHERN RIM OF THE EYEWALL. THIS IS
EVIDENT ON THE 201111Z SSSMI-S MICROWAVE IMAGERY THAT SHOWS A WELL-
DEFINED SYMMETRIC EYE WITH CONTINUOUS BANDING ALONG THE SOUTHERN
SEMI-CIRCLE. THE CURRENT POSITION IS BASED ON SATELLITE ANIMATION AND
EXTRAPOLATED FROM THE ABOVE MICROWAVE IMAGE. THE CURRENT INTENSITY IS
BASED ON DVORAK ESTIMATES FROM PGTW, RJTD, AND KNES. UPPER LEVEL
ANALYSIS INDICATES TY 15W IS APPROACHING THE BREAK IN THE RIDGE TO
THE NORTH CAUSED BY THE SHORT WAVE TROUGH CURRENTLY DIGGING SOUTHWARD
INTO SOUTHEASTERN CHINA.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK
PHILOSOPHY.
   B. TY 15W IS EXPECTED TO CONTINUE TRACKING NORTHWARD OVER THE NEXT
36 HOURS IN RESPONSE TO THE AFOREMENTIONED MID-LATITUDE TROUGH. THE
VERTICAL WIND SHEAR WILL GRADUALLY INCREASE WITH THE INCREASED UPPER
LEVEL WINDS AS THE SYSTEM APPROACHES THE SUBTROPICAL JET STREAM. THIS
WILL GRADUALLY ERODE AND WEAKEN THE SYSTEM. AFTER THE TROUGH PASSES
TO THE NORTHEAST AFTER TAU 36, THE SUBTROPICAL RIDGE WILL RE-BUILD
ALONG THE SOUTHERN BOUNDARY OF CHINA AND STEER THE SYSTEM TO THE
NORTHWEST.
   C. TYPHOON MEGI IS FORECAST TO MAKE LANDFALL EAST OF HONG KONG
AROUND TAU 60 THEN RAPIDLY DISSIPATE AS A SIGNIFICANT TROPICAL
CYCLONE. MODEL GUIDANCE IS IN LOOSE AGREEMENT WITH GFS AS THE
RIGHTMOST OUTLIER. THIS FORECAST IS JUST TO THE LEFT OF MODEL
CONSENSUS TO OFFSET GFS.//

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