Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 15w Warning Nr 41//

From: SIU Weather Processor <[email-masked]>
Date: Fri, 22 Oct 2010 21:56:13 -0500

WDPN31 PGTW 230300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W WARNING NR 41//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON 15W (MEGI), LOCATED APPROXIMATELY 230 NM EAST-
NORTHEAST OF HONG KONG, HAS TRACKED NORTHWARD AT 06 KNOTS DURING THE
PAST SIX HOURS. ANIMATED MULTI-SPECTRAL IMAGERY INDICATES THE
EYEWALL HAS COLLAPSED AND CORE CONVECTION HAS DECREASED MARKEDLY,
ESPECIALLY OVER THE WESTERN HALF OF THE STORM. INFRARED
ANIMATION SHOWS MARKED WARMING OF THE CLOUD TOPS OVER THE LOW LEVEL
CIRCULATION CENTER, YET WATER VAPOR ANIMATION VERIFIES THAT BOTH
POLEWARD AND EQUATORIAL OUTFLOW CHANNELS REMAIN WELL-DEVELOPED.
RECENT MICROWAVE IMAGERY FROM A 222116Z SSMI/S PASS ALSO VERIFIES
THAT THE MICROWAVE EYE HAS MAINTAINED INTEGRITY, BUT THE 91 GHZ
IMAGE INDICATES THAT THE UPPER LEVELS ARE BEGINNING TO TILT AWAY
FROM THE LLCC. THE SYSTEM REMAINS IN A REGION OF FAVORABLE SEA
SURFACE TEMPERATURES AND LIGHT VERTICAL WINDSHEAR, BUT AT THE
BOUNDARY LEVELS IT IS BEGINNING TO INGEST MODIFIED CONTINENTAL
POLAR (CP) AIR FLOWING OFF THE SOUTHEAST COAST OF CHINA. SURFACE
RADAR IMAGERY FROM TAIWAN INDICATES THE STORM IS MAINTAINING A
NORTHERLY TRACK TOWARD THE CHAOZHOU PROVINCE. POSITION IS BASED
PRIMARILY ON MULTISPECTRAL IMAGERY, WITH HELP FROM WEATHER RADAR
IMAGERY FROM TAIWAN. INTENSITY ANALYSIS IS BASED ON A COMBINATION OF
A DVORAK INTENSITY RATING OF 3.5 FROM PGTW AND SURFACE OBSERVATIONS
FROM COASTAL CHINA.
3. A. THE FORECAST REASONING HAS NOT CHANGED SINCE THE PREVIOUS
PROGNOSTIC REASOING BULLETIN.
   B. TYPHOON 15W IS EXPECTED TO MAKE LANDFALL OVER SOUTHEASTERN
CHINA NEAR TAU 12 AND STEADILY DISSIPATE OVER LAND. A DEEPENING
UPPER LEVEL TROUGH OVER SOUTHEASTERN CHINA WILL SUPPRESS CONVECTION
OVER THE NORTHWEST QUADRANT WHILE ENTRAINMENT OF CP AIR AT THE
BOUNDARY LEVEL WILL WEAKEN THE STORM AS IT TRACKS INLAND. THE STORM
IS EXPECTED TO TRACK ALONG THE WESTERN PERIPHERY OF A MID-LEVEL
STEERING RIDGE AND DISSIPATE OVER LAND BY TAU 36. THE DYNAMIC AIDS
ARE IN GOOD AGREEMENT THROUGH TAU 24 BUT DIVERGE SHARPLY AFTERWARD
DUE TO DIFFERENT RESPONSES TO INTERACTION WITH THE BAROCLINIC ZONE.
THE JGSM MODEL PRESENTS THE MOST COHERENT SCENARIO. THE FORECAST
THROUGH TAU 24 IS BASED ON CONSENSUS, AND AFTERWARD ON THE JGSM
MODEL AND CONSTANT RATE OF MOVEMENT.//

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