Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 15w (megi) Warning Nr 37//

From: SIU Weather Processor <[email-masked]>
Date: Thu, 21 Oct 2010 20:57:10 -0500

WDPN31 PGTW 220300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (MEGI) WARNING NR 37//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 15W (MEGI), LOCATED APPROXIMATELY 240 NM EAST-
SOUTHEAST OF HONG KONG, HAS TRACKED NORTHWARD AT 05 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS A 25-NM RAGGED EYE SURROUNDED BY A SYMMETRIC RING
OF INTENSE CONVECTION. IMAGERY INDICATES SOME PRESSURE ON THE
WESTERN PERIPHERY OF THE SYSTEM DUE TO UPPER-LEVEL WESTERLIES
AND MODERATE VERTICAL WIND SHEAR (VWS). ANIMATED WATER IMAGERY
CONTINUES TO DEPICT EXCELLENT POLEWARD OUTFLOW ENHANCED BY THE
STRONG SOUTHWESTERLY FLOW OVER EASTERN ASIA. THERE IS GOOD
CONFIDENCE IN THE CURRENT POSITION BASED ON THE EYE AND TAIWAN
RADAR FIXES. THE CURRENT INTENSITY OF 105 KNOTS IS BASED ON THE
THE PGTW CURRENT INTENSITY OF 102 KNOTS (FINAL T 77 KNOTS) AND
THE RJTD/KNES ESTIMATES OF 115 KNOTS.
3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY.
   B. TY 15W IS CURRENTLY TRACKING SLOWLY POLEWARD ALONG THE WESTERN
PERIPHERY OF THE MID-LEVEL SUBTROPICAL RIDGE (STR) POSITIONED EAST.
THE 21/12Z 500MB ANALYSIS AND SOUNDINGS (E.G., FROM ISHIGAKI-JIMA)
INDICATE WESTERLY FLOW OVER SOUTHEAST CHINA WITH A SHORTWAVE TROUGH
OVER EASTERN CHINA AND SUPPORT A STRONG STEERING STR. THE TROUGH IS
PROPAGATING NORTHEAST AND THE RIDGE IS MAINTAINING STRENGTH,
THEREFORE, THE SYSTEM IS EXPECTED TO CONTINUE TRACKING POLEWARD
THROUGH THE FORECAST PERIOD. DYNAMIC GUIDANCE IS TIGHTLY CLUSTERED
AND SUPPORTS THIS FORECAST. TY 15W IS EXPECTED TO WEAKEN THROUGH
THE PERIOD DUE TO INCREASING VWS AND SHOULD DISSIPATE OVER LAND
BETWEEN TAU 48 AND 72.//

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