Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 13w Warning Nr 18//

From: SIU Weather Processor <[email-masked]>
Date: Fri, 24 Sep 2010 09:38:04 -0500

WDPN32 PGTW 241500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 13W WARNING NR 18//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 13W (MALAKAS), LOCATED APPROXIMATELY 75 NM
NORTH-NORTHWEST OF CHICHI JIMA, JAPAN, HAS TRACKED NORTH-
NORTHEASTWARD AT 23 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED
SATELLITE IMAGERY AND A 241010Z SSMIS 91 GHZ MICROWAVE PASS DEPICT A
50 NM EYE WITH DEEP CONVECTIVE BANDING WRAPPING INTO THE CENTER FROM
THE SOUTHEASTERN QUADRANT. THE CURRENT POSITION IS BASED ON A
241132Z PGTW EYE FIX AND A MICROWAVE EYE IN THE AFOREMENTIONED SSMIS
PASS WITH GOOD CONFIDENCE. THE CURRENT INTENSITY IS HELD AT 90 KNOTS
BASED ON DVORAK CURRENT INTENSITY (CI) ESTIMATES FROM PGTW AND RJTD
OF 90 KNOTS. ANIMATED WATER VAPOR IMAGERY SHOWS ENHANCED POLEWARD
OUTFLOW ASSOCIATED WITH A DIGGING MID-LATITUDE TROUGH TO THE
NORTHWEST, HOWEVER, UPPER-LEVEL CONVERGENCE SOUTHWEST OF THE SYSTEM
IS HINDERING EQUATORWARD OUTFLOW.
3. FORECAST REASONING.
   A. THE FORECAST REASONING HAS NOT CHANGED SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. TY 13W IS CURRENTLY TRACKING ALONG THE WESTERN PERIPHERY OF A
DEEP LAYER SUBTROPICAL STEERING RIDGE. NEAR TAU 12 THE SYSTEM IS
FORECAST TO BEGIN EXTRA-TROPICAL TRANSITION AND GRADUALLY WEAKEN AS
IT ENCOUNTERS INCREASED VERTICAL ASSOCIATED WITH THE MID-LATITUDE
WESTERLIES. DURING EXTRA-TROPICAL TRANSITION (ET), TY 13W IS
EXPECTED TO REMAIN INTENSE, AS STRONG UPPER LEVEL DIFFLUENCE AND A
SHARP TEMPERATURE GRADIENT ASSOCIATED WITH THE DIGGING UPPER
LEVEL TROUGH TO THE WEST SUPPORT STRONG BAROCLINIC DEVELOPMENT. TY
13W IS EXPECTED TO COMPLETE ET BY TAU 36 AND CONTINUE TRACKING
NORTHEASTWARD AS AN INTENSE EXTRA-TROPICAL LOW. NUMERICAL MODEL
GUIDANCE REMAINS IN EXCELLENT AGREEMENT; THEREFORE THIS FORECAST IS
CLOSE TO MODEL CONSENSUS.//

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