From owner-wx-tropl@LISTSERV.ILLINOIS.EDU Tue Sep 21 22:42:51 2010 Received: from vacuum.cso.uiuc.edu (vacuum.cso.uiuc.edu [128.174.5.113]) by cozumel.ust.hk (8.13.8/8.13.8) with ESMTP id o8LEgnw4020100 for ; Tue, 21 Sep 2010 22:42:50 +0800 Received: from vacuum.cso.uiuc.edu (vacuum.cso.uiuc.edu [128.174.5.113]) by vacuum.cso.uiuc.edu (8.14.2/8.14.2) with ESMTP id o8L2kNbS028356; Tue, 21 Sep 2010 09:42:27 -0500 (CDT) Received: by LISTSERV.ILLINOIS.EDU (LISTSERV-TCP/IP release 14.5) with spool id 3508130 for WX-TROPL@LISTSERV.ILLINOIS.EDU; Tue, 21 Sep 2010 09:42:27 -0500 Received: from relay07.cites.uiuc.edu (relay07.cites.uiuc.edu [128.174.4.73]) by vacuum.cso.uiuc.edu (8.14.2/8.14.2) with ESMTP id o8LEgRSH029143 for ; Tue, 21 Sep 2010 09:42:27 -0500 (CDT) Received: from weather3.admin.niu.edu (weather3.admin.niu.edu [131.156.8.48]) by relay07.cites.uiuc.edu (8.14.4/8.14.2) with ESMTP id o8LEgKWU005477 for ; Tue, 21 Sep 2010 09:42:27 -0500 (CDT) Received: by weather3.admin.niu.edu (Postfix, from userid 501) id AB6964050021; Tue, 21 Sep 2010 09:42:20 -0500 (CDT) X-Spam-Score: 0 X-Spam-Details: rule=no-quarantine_notspam policy=no-quarantine score=0 spamscore=0 ipscore=0 phishscore=0 bulkscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx engine=5.0.0-1005130000 definitions=main-1009210071 X-Spam-OrigSender: ldm@weather3.admin.niu.edu X-Spam-Bar: Message-ID: <20100921144220.AB6964050021@weather3.admin.niu.edu> Date: Tue, 21 Sep 2010 09:42:20 -0500 Reply-To: wxmaster@COX.NET Sender: WX-TROPL Tropical Storm and Hurricane WX products From: SIU Weather Processor Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Storm 13w (malakas) Warning To: WX-TROPL@LISTSERV.ILLINOIS.EDU Precedence: list WDPN32 PGTW 211500 MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (MALAKAS) WARNING NR 06// RMKS/ 1. FOR METEOROLOGISTS. 2. 12 HOUR SUMMARY AND ANALYSIS. A. TROPICAL STORM (TS) 13W (MALAKAS), LOCATED APPROXIMATELY 230 NM NORTH-NORTHWEST OF SAIPAN, HAS TRACKED GENERALLY WEST- NORTHWESTWARD OVER THE PAST 12 HOURS UNDER THE INFLUENCE OF A WEAK LOW- TO MID-LEVEL SUBTROPICAL STEERING RIDGE ANCHORED TO THE NORTH. THE 211200Z POSITION WAS REPOSITIONED SLIGHTLY TO THE NORTH OF THE PREVIOUS POSITION BASED ON ANALYSIS OF RECENT MICROWAVE DATA (210654Z SSMI, 210744Z SSMIS, 210852Z SSMIS and 211044z SSMIS) AND A PARTIALLY-EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) EVIDENT IN RECENT ANIMATED INFRARED SATELLITE IMAGERY. IT APPEARS THE UPPER- LEVEL ANTICYCLONE PROVIDING GOOD RADIAL OUTFLOW HAS SHIFTED A BIT TO THE NORTHEAST OF THE SYSTEM, TEMPORARILY INCREASING THE VERTICAL WIND SHEAR OVER THE CYCLONE AND CAUSING THE PARTIALLY-EXPOSED LLCC. THE CURRENT INTENSITY OF 40 KNOTS IS CONSISTENT WITH DVORAK ESTIMATES FROM PGTW, KNES (BOTH T2.5) AND RJTD (T3.0). 3. FORECAST REASONING A. THE FORECAST PHILOSOPHY HAS NOT CHANGED SIGNIFICANTLY SINCE THE LAST PROGNOSTIC REASONING BULLETIN. B. TS 13W WILL CONTINUE TO TRACK GENERALLY WESTWARD OVER THE NEXT 36-48 HOURS BEFORE A DIGGING MID-LATITUDE TROUGH STARTS TO WEAKEN THE STEERING RIDGE, ENABLING THE CYCLONE TO ROUND THE RIDGE AXIS BY TAU 72. AS TS 13W APPROACHES THE RIDGE AXIS, THE SYSTEM IS EXPECTED TO INTENSIFY AS IT TRACKS OVER HIGH OCEAN HEAT CONTENT WITH GOOD POLEWARD OUTFLOW INTO A TUTT CELL LOCATED TO THE EAST OF THE CYCLONE. MALAKAS SHOULD REACH MAXIMUM INTENSITY AROUND TAU 72 DUE TO ENHANCED POLEWARD OUTFLOW INTO THE MID-LATITUDE WESTERLIES AHEAD OF THE APPROACHING TROUGH. C. AFTER CRESTING THE SUBTROPICAL RIDGE AXIS, TS 13W WILL ACCELERATE POLEWARD BY TAU 96 AND UNDERGO EXTRATROPICAL TRANSITION IN THE GRADIENT BETWEEN THE MID-LATITUDE TROUGH TO THE WEST AND A SUBTROPICAL RIDGE TO THE EAST. DURING EXTRATROPICAL TRANSITION, THE CYCLONE WILL REMAIN QUITE INTENSE AS STRONG UPPER LEVEL DIFFLUENCE AND A SHARP TEMPERATURE GRADIENT ASSOCIATED WITH THE APPROACHING TROUGH PROVIDE A STRONG BAROCLINIC DEVELOPMENT MECHANISM. THE AVAILABLE MODEL GUIDANCE IS IN VERY GOOD AGREEMENT WITH THIS TRACK PHILOSOPHY THOUGH THE GFS TRACKER CONTINUES TO REFLECT AN EARLIER POLEWARD TURN INDICATIVE OF AN UNREALISTICALLY SHALLOW SYSTEM. FOR INTENSITY, THE FORECAST IS ABOVE THE GUIDANCE IN CONSIDERATION OF THE VERY FAVORABLE UPPER-LEVEL ENVIRONMENT.// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from WX-TROPL send e-mail to LISTSERV@LISTSERV.ILLINOIS.EDU with "unsub wx-tropl" in the body of your message. For help with WX-TROPL write to cnovy@cox.net. For more information on tropical weather products, see the NHC Homepage at http://www.nhc.noaa.gov.