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

From: SIU Weather Processor <[email-masked]>
Date: Sat, 16 Oct 2010 22:09:06 -0500

WDPN31 PGTW 170300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 15W (MEGI) WARNING NR
17//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. SUPER TYPHOON (STY) 15W (MEGI), LOCATED APPROXIMATELY 450 NM
NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT
12 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY AND A 162254Z SSMIS 91H MICROWAVE IMAGE DEPICT A WELL-
DEFINED 15 NM EYE WITH A CONCENTRIC EYE WALL AND EXCELLENT RADIAL
OUTFLOW. THERE IS HIGH CONFIDENCE IN THE CURRENT POSITION BASED ON
RJTD AND PGTW 17/00Z EYE FIXES. OVER THE PAST 12 HOURS, SUPER
TYPHOON MEGI HAS UNDERGONE RAPID INTENSIFICATION. THE CURRENT
INTENSITY IS BASED ON DVORAK INTENSITY ESTIMATES 0F 140 KNOTS FROM
PGTW AND RJTD, CIMSS SATELLITE CONSENSUS ESTIMATES OF 137 KNOTS AT
16/22Z, AND AN AIRCRAFT VORTEX MESSAGE AT 16/2339Z INDICATING
MAXIMUM OBSERVED SURFACE WINDS OF 120 KNOTS, MINIMUM SEA LEVEL
PRESSURE OF 908 MB (EQUIVALENT TO 153 KNOT VMAX ON THE KNAFF-ZEHR
SCALE), AND MAXIMUM OUTBOUND SURFACE WINDS OF 146 KNOTS. UPPER LEVEL
ANALYSIS REVEALS A SLIGHT WEAKENING IN POLEWARD OUTFLOW, HOWEVER
EQUATORWARD OUTFLOW INTO AN UPPER LEVEL LOW TO THE EAST REMAINS
VIGOROUS. THE TRACK HAS FLATTENED OUT AND STY MEGI IS NOW TRACKING
WESTWARD UNDER THE INFLUENCE A DEEP-LAYER SUBTROPICAL STEERING RIDGE.
3. FORECAST REASONING.
   A. THE FORECAST INTENSITY HAS BEEN INCREASED IN RESPONSE TO THE
PAST 12 HOURS OF RAPID INTENSIFICATION.
   B. STY MEGI IS FORECAST TO CONTINUE TRACKING WESTWARD TO WEST-
SOUTHWESTWARD TOWARD LUZON AND MAY INTENSIFY SLIGHTLY WITHIN THE
NEXT 12 TO 24 HOURS. THE SYSTEM IS EXPECTED TO MAKE LANDFALL OVER
NORTHERN LUZON WITHIN THE NEXT 24 TO 36 HOURS AT SUPER TYPHOON
INTENSITY AND WEAKEN CONSIDERABLY AS IT TRACKS ACROSS THE
MOUNTAINOUS TERRAIN. AFTER TAU 36, STY MEGI WILL RE-EMERGE IN THE
SOUTH CHINA SEA AT TYPHOON INTENSITY AND BEGIN TO STEADILY RE-
INTENSIFY.
   C. NEAR TAU 72, STY MEGI IS FORECAST TO SLOW AND TURN POLEWARD
TOWARD A WEAKNESS IN THE SUBTROPICAL STEERING RIDGE ASSOCIATED WITH
A SHORTWAVE MID-LATITUDE TROUGH PROPAGATING EASTWARD ACROSS CENTRAL
ASIA. NUMERICAL MODEL GUIDANCE HAS COME INTO EVEN BETTER AGREEMENT
FROM THE PREVIOUS FORECAST, HOWEVER THERE IS SOME SPREAD IN THE
MODELS AFTER TAU 72 AS TO THE TIMING OF THE POLEWARD TURN TOWARD
SOUTHERN CHINA. THIS FORECAST IS IN CLOSE AGREEMENT WITH MODEL
CONSENSUS.//

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