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

From: SIU Weather Processor <[email-masked]>
Date: Sun, 17 Oct 2010 09:25:07 -0500

WDPN31 PGTW 171500
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 310 NM
NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-SOUTHWESTWARD AT
11 KNOTS OVER THE PAST 06 HOURS ALONG THE SOUTHERN PERIPHERY OF THE
DEEP LAYER SUBTROPICAL RIDGE TO THE NORTH. MEGI HAS INTENSIFIED TO
THE UPPER REACHES OF SUPER TYPHOON STRENGTH. CURRENT DVORAK EYE
FIXES FROM PGTW AND RJTD ESTIMATE MAXIMUM SUSTAINED SURFACE WINDS
HAVE ELEVATED 10 KNOTS FROM THE PREVIOUS FORECAST TO 155 KNOTS. A
STRENGTHENED POLEWARD OUTFLOW CHANNEL HAS SUPPORTED THIS
INTENSIFICATION, IN ADDITION TO SUSTAINED EQUATORWARD OUTFLOW INTO A
TROPICAL UPPER LEVEL TROPOSPHERIC TROUGH CELL TO THE EAST. EYE
TEMPERATURES HAVE REMAINED STEADY AT AROUND 15 DEG CELCIUS AND THE
EYE DIAMETER HAS RANGED FROM 20 TO 25 NM.
3. FORECAST REASONING.
   A. THIS FORECAST REFLECTS A HIGHER INITIAL INTENSITY THAN
PREVIOUSLY FORECAST.
   B. OUTER RAINBANDS HAVE ALREADY BEGUN TO AFFECT LUZON. THE SYSTEM
CENTER IS EXPECTED TO TRACK OVER LUZON IN LESS THAN 12 HOURS AND
WILL WEAKEN CONSIDERABLY OVER THE RUGGED TOPOGRAPHY. IT WILL EMERGE
INTO THE SOUTH CHINA SEA AROUND 18/12Z, REORGANIZE, AND GRADUALLY
STRENGTHEN. AROUND THIS TIME THE STEERING RIDGE WILL BEGIN TO WEAKEN
AND THE SYSTEM WILL SLOW AND TURN NORTH OF WEST TO THE EAST OF
HAINAN. MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT FROM SIX HOURS
AGO. GFS REMAINS THE LONE OUTLIER THROUGH THE FIRST 48 HOURS AND
STALLS THE CYCLONE OFF THE WEST COAST OF LUZON FOR 1 TO 2 DAYS, THEN
JERKS THE TRACK PECULIARLY NORTHEAST. THE REST OF THE MODEL PACKING
RIDES THE SOUTHERN PERIPHERY OF THE WEAKENING/RETREATING STEERING
RIDGE TO THE WEST THEN NORTHWEST, TO INCLUDE NOGAPS.
   C. IN THE EXTENDED FORECAST MEGI WILL TURN TOWARDS A BUILDING
WEAKENESS IN THE STEERING RIDGE OVER SOUTHERN CHINA. MODEL FIELDS
INDICATE A SHORT WAVE TROUGH AS THE SOURCE OF THIS WEAKNESS. THERE
IS INCREASED UNCERTAINTY IN THE INTENSITY FORECAST GIVEN THE WIDE
RANGE AMONG THE INTENSITY GUIDANCE. NONTHELESS, THE 15Z JTWC
FORECAST REMAINS CONSISTENT WITH A REINTENSIFICATION SCENARIO.//

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
To unsubscribe from WX-TROPL send e-mail to [email-masked] with
"unsub wx-tropl" in the body of your message. For help with WX-TROPL
write to [email-masked]. For more information on tropical weather products, see the NHC Homepage at http://www.nhc.noaa.gov.