Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 12w Warning Nr 14//

From: SIU Weather Processor <[email-masked]>
Date: Fri, 17 Sep 2010 21:17:05 -0500

WDPN31 PGTW 180300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W WARNING NR 14//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 12W (FANAPI), LOCATED APPROXIMATELY 270 NM EAST-
SOUTHEAST OF TAIPEI, TAIWAN, HAS TRACKED WESTWARD AT 07 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL IMAGERY SHOWS A 20
NM EYE AND A 172216Z SSMIS MICROWAVE IMAGE DEPICTS MULTIPLE
CONVECTIVE BANDS ALONG THE EASTERN PERIPHERY. THERE IS HIGH
CONFIDENCE IN THE INITIAL POSITION BASED ON AN EYE FIX. THE INITIAL
INTENSITY IS BASED ON THE 172301Z AND 180006Z VORTEX DATA MESSAGES
INDICATING SURFACE WIND SPEED ESTIMATES OF 93 AND 95 KNOTS. THERE IS
ALSO HIGH CONFIDENCE IN THE WIND RADII STRUCTURE, WHICH WAS BASED ON
DOTSTAR DROPSONDE OBSERVATIONS. UPPER LEVEL ANALYSIS INDICATES
INCREASED NORTHEASTERLY VERTICAL WIND SHEAR ALONG THE NORTHERN
PERIPHERY OF THE SYSTEM. ADDITIONALLY, WATER VAPOR SATELLITE IMAGERY
SHOWS EXCELLENT UPPER LEVEL EQUATORWARD OUTFLOW AND DECREASING
POLEWARD OUTFLOW AS A MID-LATITUDE TROUGH MOVES FARTHER
NORTHEASTWARD. TY 12W IS CURRENTLY TRACKING ALONG THE SOUTHERN
PERIPHERY OF A SUBTROPICAL STEERING RIDGE LOCATED TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY AND TRACK SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 12W IS FORECAST TO CONTINUE TRACKING WESTWARD ALONG THE
SOUTHERN PERIPHERY OF THE SUBTROPICAL STEERING RIDGE THROUGHOUT THE
FORECAST PERIOD. ALTHOUGH POLEWARD OUTFLOW IS DECREASING, FAVORABLE
EQUATORWARD OUTFLOW WILL ALLOW TY FANAPI TO SLIGHTLY INCREASE IN
INTENSITY WITHIN THE NEXT 12 HOURS. AFTER TAU 24, TY FANAPI IS
EXPECTED TO MAKE LANDFALL OVER TAIWAN, WHERE IT WILL WEAKEN
SIGNIFICANTLY. THE SYSTEM SHOULD CONTINUE WESTWARD MAKING LANDFALL
OVER CHINA BY TAU 48. NUMERICAL MODEL GUIDANCE IS IN TIGHT
AGREEMENT, THEREFORE THERE IS HIGH CONFIDENCE IN THE TRACK FORECAST.
   C. IN THE EXTENDED PERIOD, TY 12W IS EXPECTED TO DISSIPATE BY
TAU 96.//

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