Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 15w (megi) Warning Nr 33//

From: SIU Weather Processor <[email-masked]>
Date: Wed, 20 Oct 2010 21:08:06 -0500

WDPN31 PGTW 210300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (MEGI) WARNING NR 33//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 15W (MEGI), LOCATED APPROXIMATELY 250 NM SOUTHEAST
OF HONG KONG, HAS TRACKED NORTHWARD AT 06 KNOTS OVER THE PAST SIX
HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A LARGE,
RAGGED 40NM EYE SURROUNDED BY A FAIRLY SYMMETRIC RING OF DEEP
CONVECTION. ANIMATED WATER VAPOR IMAGERY DEPICTS EXCELLENT RADIAL
OUTFLOW WITH ENHANCED POLEWARD OUTFLOW ASSOCIATED WITH A MIDLATITUDE
SHORTWAVE TROUGH DEEPENING OVER SOUTHEAST CHINA. THERE IS GOOD
CONFIDENCE IN THE CURRENT POSITION BASED ON THE EYE. THE CURRENT
INTENSITY OF 100 KNOTS IS BASED ON AN AVERAGE OF DVORAK ESTIMATES
RANGING FROM 90 TO 115 KNOTS AS WELL AS THE RECENT SATCON ESTIMATE
OF 97 KNOTS.
3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY.
   B. THE 20/12Z 500MB ANALYSIS DEPICTS A SHARP MIDLATITUDE
SHORTWAVE TROUGH OVER EASTERN CHINA WITH WESTERLY FLOW ACROSS
SOUTHEAST CHINA AND A SUBTROPICAL RIDGE POSITIONED EAST OF THE
SYSTEM. OVER THE PAST 24 HOURS, THE DYNAMIC MODELS HAVE BECOME
MORE STABLE AND ARE IN GOOD AGREEMENT THROUGH TAU 48, SUPPORTING THE
POLEWARD TRACK. AFTER TAU 36, TY 15W IS FORECAST TO ENCOUNTER STRONG
VERTICAL WIND SHEAR AND SHOULD WEAKEN RAPIDLY AND DE-COUPLE.
SUBSEQUENTLY, MODEL GUIDANCE DIVERGES AND THERE IS INCREASED
UNCERTAINTY IN THE LATER TAUS. THE CURRENT FORECAST FAVORS A
NORTHWESTWARD TURN INTO CHINA UNDER THE STEERING INFLUENCE OF LOW-
LEVEL NORTHEASTERLY FLOW ASSOCIATED WITH A BROAD HIGH PRESSURE
SYSTEM OVER KOREA/JAPAN.
   C. TY 15W IS FORECAST TO DISSIPATE BY TAU 96.//

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