Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 12w Warning Nr 18//

From: SIU Weather Processor <[email-masked]>
Date: Sun, 19 Sep 2010 09:39:10 -0500

WDPN31 PGTW 190300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W WARNING NR 18//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
TYPHOON (TY) 12W (FANAPI), LOCATED APPROXIMATELY 140 NM SOUTHWEST OF
TAIPEI, TAIWAN, HAS TRACKED WESTWARD AT 11 KNOTS OVER THE PAST SIX
HOURS. ANIMATED INFRARED (IR) SATELLITE IMAGERY AND A TAIWAN RADAR
LOOP INDICATE TY 12W HAS RE-EMERGED OVER WATER IN THE TAIWAN STRAIT.
THE AFOREMENTIONED RADAR LOOP AND IR IMAGERY AS WELL AS A 191100Z 91
GHZ SSMIS MICROWAVE IMAGE SHOW A MAJORITY OF THE DEEP CONVECTION
ALONG THE SOUTHERN SEMI-CIRCLE OF THE SYSTEM, WHILE CONVECTION ALONG
THE NORTHERN SEMI-CIRCLE HAS WEAKENED CONSIDERABLY DUE TO LAND
INTERACTION WITH TAIWAN. THERE IS FAIR CONFIDENCE IN THE CURRENT
POSITION BASED ON THE SSMIS IMAGE AND A WEAKLY DEFINED EYE FEATURE
IN THE RADAR LOOP. CURRENT INTENSITY IS BASED ON DVORAK ESTIMATES
FROM PGTW, AND RJTD OF 65 TO 70 KNOTS. OBSERVATIONS FROM KAOHSIUNG,
TAIWAN (40 NM SOUTH OF TY FINAPI'S TRACK) INDICATED MAX WINDS OF 40
KNOTS GUSTING TO 60 KNOTS AT 19/06Z. ANIMATED WATER VAPOR IMAGERY
CONTINUES TO SHOW ENHANCED EQUATORWARD OUTFLOW ASSOCIATED WITH A
DIGGING UPPER LEVEL TROUGH TO THE EAST OF TY 12W. HOWEVER, POLEWARD
OUTFLOW CONTINUES TO BE RESTRICTED BY AN ANTICYCLONE NORTH OF THE
SYSTEM CAUSING INCREASED NORTHEASTERLY VERTICAL WIND SHEAR.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE IN THE OVERALL FORECAST PHILOSOPHY FROM THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 12W IS FORECAST TO CONTINUE TRACKING ALONG THE SOUTHERN
PERIPHERY OF A SUBTROPICAL STEERING RIDGE ANCHORED OVER NORTHEASTERN
CHINA THROUGHOUT THE FORECAST PERIOD. THE SYSTEM IS FORECAST TO RE-
INTENSIFY SLIGHTLY AS IT TRACKS ACROSS THE TAIWAN STRAIT BEFORE
MAKING LANDFALL OVER EASTERN CHINA NEAR TAU 12. TY 12W IS EXPECTED
TO RAPIDLY WEAKEN AS IT CONTINUES TO TRACK WESTWARD OVER INLAND
CHINA AND DISSIPATE AS A SIGNIFICANT TROPICAL CYCLONE BY TAU 48.
NUMERICAL MODEL GUIDANCE REMAINS TIGHTLY PACKED THROUGHOUT THE
FORECAST PERIOD; THEREFORE THIS FORECAST IS CLOSE TO MODEL
CONSENSUS.//

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