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

From: SIU Weather Processor <[email-masked]>
Date: Sun, 17 Oct 2010 21:38:10 -0500

WDPN31 PGTW 180300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 15W (MEGI) WARNING NR
19//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. SUPER TYPHOON (STY) 15W (MEGI), LOCATED APPROXIMATELY 220 NM
NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 09 KNOTS
OVER THE PAST SIX HOURS ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL STEERING RIDGE. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
AND A 172242Z SSMIS 91H MICROWAVE IMAGE DEPICT A CIRCULAR 27 NM EYE
WITH A DEEP CONVECTIVE EYE WALL. THERE IS HIGH CONFIDENCE IN THE
CURRENT POSITION BASED ON CONCURRENT DVORAK EYE FIXES FROM PGTW AND
RJTD AT 18/00Z. THE CURRENT INTENSITY IS BASED ON DVORAK ESTIMATES
RANGING FROM 140 TO 155 KNOTS FROM PGTW, KNES, AND RJTD. WHILE THE
POLEWARD OUTFLOW CHANNEL AND EQUATORWARD OUTFLOW HAVE SUSTAINED OVER
THE PAST SIX HOURS, ENHANCED INFRARED SATELLITE IMAGERY INDICATES A
SLIGHT WEAKENING ALONG THE NORTHWESTERN QUADRANT OF THE SYSTEM DUE
TO INCREASED LAND INTERACTION.
3. FORECAST REASONING.
   A. THE FORECAST REASONING HAS NOT CHANGED SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. STY MEGI IS WITHIN SIX HOURS OF MAKING LANDFALL NEAR CAGAYAN
AND ISABELA PROVINCES IN NORTHERN LUZON. THE SYSTEM IS EXPECTED TO
WEAKEN CONSIDERABLY, BUT SUSTAIN TYPHOON STRENGTH AS CROSSES THE
CORDILLERA MOUNTAIN RANGE AND RE-EMERGES IN THE SOUTH CHINA SEA
BETWEEN TAU 12 AND TAU 24. STY MEGI IS EXPECTED TO RE-ORGANIZE AND
GRADUALLY RE-INTENSIFY AS IT TRACKS SLOWLY NORTH OF WEST TOWARD A
WEAKNESS IN THE SUBTROPICAL STEERING RIDGE. NUMERICAL MODEL GUIDANCE
IS IN GOOD AGREEMENT IN THE EARLY TAUS. GFS REMAINS THE ONLY
OUTLIER, STALLING THE SYSTEM OFF THE WESTERN COAST OF LUZON UNTIL
TAU 48, AND THEN DRIVING THE SYSTEM INTO THE DEEP-LAYER RIDGE TOWARD
TAIWAN. THIS DOES NOT SEEM TO MAKE SENSE, ESPECIALLY WITH INCREASING
500 MB HEIGHTS ANALYZED OVER SOUTH EASTERN CHINA AND TAIWAN OVER THE
PAST 36 HOURS.
   C. IN THE EXTENDED TAUS STY MEGI IS FORECAST TO SLOWLY INTENSIFY
THROUGH TAU 72, BUT THEN WEAKEN AS IT MOVES OVER COOLER WATERS ALONG
THE SOUTH CHINA COAST. THERE IS SOME UNCERTAINTY AS TO WHERE THE
SYSTEM WILL MAKE LANDFALL BASED ON THE SPREAD IN THE NUMERICAL MODEL
GUIDANCE IN THE LATER TAUS. UKMO AND ECMWF ARE ALONG THE THE
SOUTHERN EDGE OF THE AIDS ENVELOPE AND TRACK THE SYSTEM TOWARD
EASTERN HAINAN, NOGAPS AND WBAR LIE ALONG THE NORTHERN EDGE OF THE
AIDS ENVELOPE TRACKING THE SYSTEM TOWARD HONG KONG, AND GFDN IS
SPLIT IN THE MIDDLE. THIS FORECAST IS CONSISTENT WITH THE PREVIOUS
FORECAST AND SLIGHTLY SOUTH OF MODEL CONSENSUS.//

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