Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 15w (megi) Warning Nr 13//

From: SIU Weather Processor <[email-masked]>
Date: Fri, 15 Oct 2010 22:08:08 -0500

WDPN31 PGTW 160300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (MEGI) WARNING NR 13//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON 15W (MEGI), LOCATED APPROXIMATELY 705 NM EAST-
NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT
15 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY AND A 152017Z SSMIS 91H MICROWAVE IMAGE DEPICT A WELL
DEFINED LOW-LEVEL CIRCULATION CENTER WITH TIGHTLY CURVED CONVECTIVE
BANDING (TCB) WRAPPING IN FROM THE SOUTHEASTERN QUADRANT. ANIMATED
WATER VAPOR IMAGERY INDICATES GOOD EQUATORWARD OUTFLOW, WHILE
POLEWARD OUTFLOW HAS YET TO BE ENHANCED BY A PASSING MID-LATITUDE
SHORTWAVE TROUGH NORTH OF THE SYSTEM. TY 15W IS CURRENTLY
EXPERIENCING SOME DEFORMATION ALONG ITS NORTHWESTERN QUADRANT
ASSOCIATED WITH AN UPPER LEVEL LOW, WHICH APPEARS TO BE FILLING
SLOWLY. THERE IS HIGH CONFIDENCE IN THE CURRENT POSITION BASED ON
THE TCB AND A MICROWAVE EYE IN A PARTIAL 160032Z TRMM 37H MICROWAVE
PASS. THE CURRENT INTENSITY IS BASED ON DVORAK ESTIMATES OF 90 KNOTS
FROM RJTD, PGTW, AND KNES.
3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY.
   B. TY 15W HAS CONTINUED TO TRACK NORTHWESTWARD ALONG THE
SOUTHWESTERN PERIPHERY OF THE MID-LEVEL SUBTROPICAL RIDGE (STR)
TOWARD A WEAKNESS ASSOCIATED WITH A PASSING MID-LATITUDE SHORTWAVE
TROUGH. WITHIN THE NEXT 12 HOURS, AS THE TROUGH CONTINUES TO
PROPAGATE NORTHEASTWARD, THE STR IS EXPECTED TO RE-BUILD TO THE WEST
ALLOWING THE SYSTEM TO TRACK WESTWARD TOWARD LUZON. POLEWARD OUTFLOW
IS EXPECTED TO INCREASE AND THE UPPER LEVEL LOW TO THE WEST OF TY
15W IS EXPECTED TO FILL, RELIEVING THE PRESSURE ALONG THE
NORTHWESTERN QUADRANT, AND ALLOWING THE SYSTEM TO UNDERGO STEADY
INTENSIFICATION THROUGH TAU 48. TY MEGI IS FORECAST TO MAKE LANDFALL
OVER NORTHERN LUZON BETWEEN TAU 48 AND TAU 72 AT OR NEAR SUPER
TYPHOON INTENSITY AND SHOULD WEAKEN CONSIDERABLY AS IT CROSSES THE
MOUNTAINOUS TERRAIN OF LUZON. UKMO, JGSM, ECMWF AND GFS MODEL
TRACKERS REMAIN TIGHTLY CLUSTERED AND CONSISTENT WITH A GENERALLY
WESTWARD TRACK OVER LUZON. GFDN HAS CONSISTENTLY INDICATED A WEST-
NORTHWESTWARD TRACK TOWARD TAIWAN, WHILE NOGAPS HAS SETTLED ON A
POLEWARD TRACK TOWARD OKINAWA OVER THE PAST 3 MODEL RUNS. THE
NOGAPS TRACK CONTINUES TO MAKE LITTLE SENSE AS IT APPEARS TO BE
EXAGGERATING THE SOUTHERN EXTENT OF THE MID-LATITUDE TROUGH AS WELL
AS DRIVING THE SYSTEM INTO A STRONG, BROAD LOW-LEVEL HIGH SITUATED
OVER EASTERN CHINA. THE GFDN MODEL SOLUTION ALSO REMAINS
QUESTIONABLE AS IT CONTINUES TO TRACK THE SYSTEM INTO A FAIRLY
STRONG LOW TO MID-LEVEL STEERING RIDGE SITUATED OVER EASTERN CHINA.
BASED ON THIS ANALYSIS, THE CURRENT FORECAST FAVORS A TRACK SLIGHTLY
SOUTH AND FASTER THEN MODEL CONSENSUS, SIMILAR TO THE UKMO, JGSM,
ECMWF, AND GFS MODEL TRACKERS.
   C. NEAR TAU 72, TY 15W IS FORECAST TO RE-EMERGE IN THE SOUTH
CHINA SEA AT TYPHOON INTENSITY AND TRACK GENERALLY WESTWARD TOWARD
HAINAN. THIS FORECAST CONTINUES TO FAVOR THE SOUTHERN CLUSTER OF
MODELS.//

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