Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 15w (megi) Warning Nr 35//

From: SIU Weather Processor <[email-masked]>
Date: Thu, 21 Oct 2010 09:14:05 -0500

WDPN31 PGTW 211500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (MEGI) WARNING NR 35//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 15W (MEGI), LOCATED APPROXIMATELY 245 NM EAST-
SOUTHEAST OF HONG KONG, HAS TRACKED NORTH-NORTHEASTWARD AT 04 KNOTS
OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY SHOWS A
RAGGED 40 NM EYE THAT IS RINGED BY FLARING POCKETS OF DEEP
CONVECTION EMBEDDED WITHIN A SHALLOWER CLOUD DECK. THE SYSTEM HAS
MAINTAINED A 100 KNOT INTENSITY BASED ON DVORAK FIXES FROM PGTW AND
RJTD THAT INDICATE THE SYSTEM RANGES FROM 100 TO 115 KNOTS. BECAUSE
THE EYE HAS ENLARGED THE CURRENT POSITION IS BASED ON A 211131Z
SSMIS 37H MICROWAVE IMAGE, WHICH SHOWS THAT THE LOW LEVEL
CIRCULATION CENTER IS TO THE EAST OF BOTH THE PGTW AND RJTD
POSITIONS. THE CYCLONE CONTINUES TO TRACK POLEWARD TOWARDS A
WEAKNESS IN THE DEEP LAYER STEERING RIDGE TO THE NORTH ALONG THE
WESTERN EXTENT OF A DEEP LAYER STEERING RIDGE TO THE EAST. STRONG
POLEWARD VENTING HAS AIDED THE CYCLONE IN MAINTAINING ITS INTENSITY
OF 100 KNOTS.
3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY.
   B. MODEL GUIDANCE CONTIUNES TO SUPPORT A POLEWARD TRACK TOWARDS
CHINA. THE CURRENT FORECAST HAS BEEN SHIFTED FURTHER EAST IN
RESPONSE TO THE CURRENT MOTION OF THE SYSTEM TO THE NORTH-NORTHEAST.
THIS PLACES THE FORECAST CLOSER TO THE MODEL CONSENSUS, BUT STILL TO
THE WEST. THE SYSTEM WILL CONTINUE TO TRACK JUST EAST OF NORTH ALONG
THE DEEP LAYER RIDGE TOWARDS THE BASE OF MID TO UPPER LEVEL
SHORTWAVE TROUGH OVER SOUTHEASTERN ASIA. VERTICAL WIND SHEAR WILL
BEGIN TO AFFECT THE SYSTEM JUST PRIOR TO LANDFALL. IN THE INTERIM,
MODERATE TO STRONG POLEWARD OUTFLOW WILL MODIFY THE RATE OF
WEAKENING. THE CYCLONE WILL QUICKLY DISSIPATE OVER SOUTHEASTERN ASIA
ONCE DECOUPLED FROM ITS SHEARD DEEP CONVECTION, TRACKING WESTWARD
WITH THE LOW LEVEL FLOW OUT OF THE ANTICYCLONE TO THE NORTH.
   C. TY 15W IS FORECAST TO DISSIPATE BY TAU 72.//

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