Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 12w Warning Nr 12//

From: SIU Weather Processor <[email-masked]>
Date: Fri, 17 Sep 2010 08:58:06 -0500

WDPN31 PGTW 171500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W WARNING NR 12//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 12W (FANAPI), LOCATED APPROXIMATELY 360 NM EAST-
SOUTHEAST OF TAIPEI, TAIWAN, HAS TRACKED NORTHWESTWARD AT 05 KNOTS
OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY
INDICATES THAT THE SYSTEM HAS CONTINUED TO CONSOLIDATE AND NOW
HAS AN 11 NM EYE. A 170944Z SSMIS IMAGE SHOWS A NEAR COMPLETE
EYEWALL WITH A SMALL GAP IN THE NORTH QUADRANT, AND EXCELLENT
MULTIPLE CONVECTIVE BANDING OVER THE EASTERN SEMI-CIRCLE. UPPER-
LEVEL FEATURE TRACK WINDS INDICATE THAT CONVERGENT NORTHEASTERLY
FLOW ASSOCIATED WITH THE STRONG HIGH BUILDING NORTH OF THE SYSTEM
IS LIKELY HINDERING DEVELOPMENT OVER THE NORTHWEST QUADRANT.
VERTICAL WIND SHEAR (VWS) VALUES HAVE INCREASED 5-10 KNOTS OVER
THE PAST 24 HOURS. THERE IS HIGH CONFIDENCE IN THE CURRENT
POSITION AND 6-HOUR MOTION BASED ON THE EYE FEATURE. IN FACT,
THE SYSTEM IS TRACKING WEST-NORTHWESTWARD OVER THE PAST FEW
HOURS. THE CURRENT INTENSITY IS ASSESSED AT 85 KNOTS BASED ON
AN AVERAGE OF DVORAK ESTIMATES RANGING FROM 77 TO 90 KNOTS FROM
PGTW AND RJTD.
3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY AND TRACK SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. THE 500MB ANALYSES OVER THE PAST 24 HOURS INDICATE THAT THE
SUBTROPICAL RIDGE (STR) IS BUILDING ACROSS THE EAST CHINA SEA INTO
WESTERN JAPAN (24-HOUR HEIGHT RISES OF 20-30 METERS) BEHIND THE
MIDLATITUDE SHORT-WAVE TROUGH (WHICH HAD BRIEFLY INTERACTED WITH
THE SYSTEM CAUSING A SHORT-TERM NORTHEASTWARD TRACK). THIS
TROUGH IS FILLING AND KICKING OUT NORTHEASTWARD INTO NORTHEAST
JAPAN. UPPER-LEVEL WINDS AT NAZE (28N 129E) HAVE SUBSEQUENTLY
STRENGTHENED AND SHIFTED TO THE NORTH-NORTHEAST WITH INCREASING
SUBSIDENCE THROUGH THE MID- AND UPPER-LEVELS. BASED ON THIS
ANALYSIS AND THE TIGHT MODEL AGREEMENT, TY 12W IS FORECAST TO
TRACK WESTWARD UNDER THE STEERING INFLUENCE OF THE DEEP STR
THROUGH THE FORECAST PERIOD. TY 12W IS EXPECTED TO PEAK IN
INTENSITY IN THE NEXT 12-24 HOURS AT 90-100 KNOTS. THE SYSTEM
RETAINS GOOD EQUATORWARD OUTFLOW, HOWEVER, POLEWARD OUTFLOW IS
WEAKENING AS THE HIGH BUILDS TO THE NORTH. VWS IS EXPECTED TO
INCREASE AND WILL LIMIT INTENSIFICATION AFTER TAU 24 BUT PERHAPS
AS EARLY AS TAU 12. THE SYSTEM WILL MAKE LANDFALL OVER TAIWAN AFTER
TAU 36 AND SHOULD WEAKEN SIGNIFICANTLY BEFORE RE-EMERGING OVER
THE THE TAIWAN STRAIT AS A 50-60 KNOT SYSTEM. FANAPI WILL
CONTINUE TRACKING WESTWARD AND SHOULD MAKE LANDFALL OVER CHINA
BY TAU 72.
   C. IN THE EXTENDED PERIOD, TY 12W IS EXPECTED TO DISSIPATE BY
TAU 96.//

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