Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 15w (megi) Warning Nr 39//

From: SIU Weather Processor <[email-masked]>
Date: Fri, 22 Oct 2010 09:04:10 -0500

WDPN31 PGTW 221500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (MEGI) WARNING NR 39//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 15W (MEGI), LOCATED APPROXIMATELY 235 NM EAST OF
HONG KONG, HAS TRACKED NORTHWARD AT 06 KNOTS OVER THE PAST SIX
HOURS. THE TY HAS CONTINUED TO TRACK ALONG THE WESTERN EXTENT OF A
DEEP LAYER STEERING RIDGE TO THE EAST TOWARDS THE CHINESE COASTLINE.
LANDFALL IS EXPECTED TO OCCUR IN MUCH THE SAME PLACE AND SAME
INTENSITY AS FORECAST TWELVE HOURS AGO. THE SYSTEM HAS BEGUN TO
WEAKEN UNDER THE INFLUENCE OF MODERATE VERTICAL WIND SHEAR AND
INCREASED SUBSIDENCE. THE CENTRAL CONVECTION HAS SHALLOWED AND
CONTRACTED TOWARDS THE CENTER AND THE LARGE EYE HAS BECOME
COMPLETELY CLOUD FILLED. THE INITIAL INTENSITY IS BASED ON FALLING
DVORAK ESTIMATES FROM PGTW, WHICH INDICATE THE INTENSITY RANGES FROM
77 TO 102 KNOTS. THE CURRENT POSITION IS BASED ON A 221047Z SSMIS
MICROWAVE IMAGE, IN ADDITION TO POSITION FIXES FROM PGTW AND RJTD,
AND PLACES THE SYSTEM TO THE SOUTH OF A STATIONARY BOUNDARY.
COMPARISON OF HIGH AND LOW MICROWAVE FREQUENCIES SUGGESTS THAT THE
UPPER LEVEL CIRCULATION IS BEGINNING TO TILT TO THE NORTHEAST OF THE
LOW LEVEL CIRCULATION CENTER.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY.
   B. TY 15W WILL CONTINUE TO WEAKEN AS IT TRACKS NORTH TOWARDS
CHINA. A SHORTWAVE TROUGH IS CURRENTLY DIGGING TO THE WEST OF THE TY
AND IS INCITING INCREASED VERTICAL WIND SHEAR AND SUBSIDENCE. THE
BASE OF THE TROUGH IS WELL SOUTH OF THE TY'S CURRENT LATITUDE.
LANDFALL IS EXPECTED WITHIN TWELVE HOURS NEAR 75 KNOTS. THE SYSTEM
WILL QUICKLY DISSIPATE OVER CHINA WITHIN TWELVE TO EIGHTEEN HOURS OF
LANDFALL, AND INCORPORATE INTO THE STATIONARY BOUNDARY. ALL THE
MODEL TRACKERS BRING THE TY ASHORE WITHIN TWELVE HOURS WITH THE
EXCEPTION OF THE EGRR TRACKER. THE 22/1500Z FORECAST LIES NEAR THE
PREVIOUS FORECAST AND CLOSE TO THE MODEL CONSENSUS.//

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