Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 15w (megi) Warning Nr 11//

From: SIU Weather Processor <[email-masked]>
Date: Fri, 15 Oct 2010 09:28:12 -0500

WDPN31 PGTW 151500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (MEGI) WARNING NR 11//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON 15W (MEGI), LOCATED APPROXIMATELY 850 NM EAST OF
MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 11 KNOTS OVER THE
PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY AND A 151059Z
SSMIS 37H IMAGE DEPICT A WELL-DEFINED LOW-LEVEL CIRCULATION CENTER
(LLCC) WITH TIGHTLY-CURVED BANDING (TCB). ANIMATED WATER VAPOR
IMAGERY INDICATES GOOD OVERALL OUTFLOW WITH THE EXCEPTION OF THE
NORTHWEST QUADRANT, WHERE OUTFLOW IS HINDERED BY A TUTT LOW NEAR 20N
130E AND UPPER-LEVEL TROUGHING EXTENDING SOUTHWESTWARD. THERE IS
HIGH CONFIDENCE IN THE CURRENT POSITION BASED ON THE TCB AND
AFOREMENTIONED SSMIS IMAGE. THE CURRENT INTENSITY OF 90 KNOTS IS
BASED ON DVORAK ESTIMATES OF 90 KNOTS FROM BOTH KNES AND PGTW. RJTD
IS CURRENTLY AT 70 KNOTS.
3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY.
   B. TY 15W HAS CONTINUED TO TRACK NORTHWESTWARD ALONG THE SOUTHWEST
PERIPHERY OF THE MID-LEVEL SUBTROPICAL RIDGE (STR) TOWARD A WEAKNESS
POSITIONED JUST SOUTH OF OKINAWA. THE 15/00Z UPPER AIR ANALYSES SHOW
A MAJOR MIDLATITUDE SHORTWAVE TROUGH OVER NORTHEASTERN ASIA WITH THE
AXIS ALONG 128E. THE STR HAS REMAINED STRONG AND EXTENDS FROM A HIGH
CENTERED NEAR 24N 133E WESTWARD TO 130E. THIS STR IS EXPECTED TO
STRENGTHEN AS THE TROUGH PROPAGATES NORTHEASTWARD IN THE NEXT 24
HOURS. THIS WILL ALLOW TY 15W TO TURN MORE WESTWARD TOWARD NORTHERN
LUZON. TY 15W SHOULD CONTINUE TO INTENSIFY UNDER FAVORABLE (INCLUDING
IMPROVING OUTFLOW AS THE TUTT LOW WEAKENS) CONDITIONS THROUGH TAU 72,
AND IS EXPECTED TO REACH SUPER TYPHOON STRENGTH BEFORE MAKING
LANDFALL OVER LUZON. MODEL GUIDANCE, INCLUDING UKMO, JGSM, ECMWF AND
GFS (AS WELL AS ALMOST ALL ENSEMBLE SOLUTIONS), IS TIGHTLY CLUSTERED
AND SHOWS A GENERALLY WESTWARD TRACK. THE ONLY OUTLIERS ARE NOGAPS,
WBAR AND GFDN. GFDN HAS CONSISTENTLY INDICATED A WEST-NORTHWESTWARD
TRACK TOWARD TAIWAN WHILE NOGAPS HAS BEEN HIGHLY ERRATIC OVER THE
PAST 5 RUNS AND NOW INDICATES A RE-CURVE TRACK TOWARD OKINAWA. THE
CURRENT NOGAPS TRACK MAKES LITTLE SENSE AS THE SYSTEM IS TRACKING
INTO A STRONG, BROAD LOW-LEVEL HIGH SITUATED OVER NORTHEAST ASIA
(INTO LOW-LEVEL NORTHEASTERLY FLOW) AND ALSO TRACKS THE SYSTEM
THROUGH AN UPPER-LEVEL RIDGE. THEREFORE, THE NOGAPS SOLUTION IS
DISCOUNTED. THE GFDN SOLUTION IS ALSO PROBLEMATIC WITH A TRACK INTO
THE WESTERN STEERING RIDGE. BASED ON THIS ANALYSIS, THE CURRENT
FORECAST IS POSITIONED SOUTH AND FASTER THAN THE CONSENSUS TO OFFSET
THESE OUTLIERS AND FAVORS THE TIGHT CLUSTER OF UKMO, ECMWF, GFS AND
JGSM.
   C. AFTER TAU 72, TY 15W IS FORECAST TO MAKE LANDFALL OVER LUZON
AT OR NEAR SUPER TYPHOON STRENGTH. THE SYSTEM SHOULD WEAKEN
CONSIDERABLY WHILE CROSSING THE MOUNTAINOUS TERRAIN OF LUZON BUT IS
EXPECTED TO RE-EMERGE INTO THE SOUTH CHINA SEA AT TYPHOON STRENGTH.
THIS FORECAST CONTINUES TO FAVOR THE SOUTHERN CLUSTER OF MODELS.//

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