Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Storm 10w Warning Nr 08//

From: SIU Weather Processor <[email-masked]>
Date: Fri, 3 Sep 2010 09:13:08 -0500

WDPN33 PGTW 031500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 10W WARNING NR 08//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 10W (MALOU), LOCATED APPROXIMATELY 130 NM
SOUTHEAST OF KADENA AB, OKINAWA JAPAN, HAS TRACKED WEST-NORTHWEST-
WARD AT 20 KNOTS OVER THE PAST SIX HOURS. ANIMATED WATER VAPOR
IMAGERY SHOWS MODERATE OUTFLOW ON THE NORTHEAST QUADRANT WITH
SUSTAINED DEEP CONVECTION THAT IS MOSTLY TO THE SOUTHEAST OF THE LOW
LEVEL CIRCULATION CENTER (LLCC). THE SAME ANIMATION ALSO SHOWS A TUTT
CELL TO THE WEST THAT IS IMPINGING THE OUTFLOW ALONG THE WESTERN
FLANK OF THE SYSTEM. THE CURRENT POSITION IS BASED ON ANIMATED
MULTISPECTRAL IMAGERY AND EXTRAPOLATED FROM A 031059Z SSMI-S
MICROWAVE IMAGE SHOWING A DETACHED LLCC FROM THE MAIN CONVECTION.
CONFIDENCE IN THIS POSITION IS POOR. THE CURRENT INTENSITY IS
AVERAGED FROM DVORAK ESTIMATES OF 35 KNOTS FROM PGTW, KNES, AND RJTD.
THE RECENT STORM MOTION IS MORE WESTWARD THAN THE PREVIOUS TRACK
WHICH MAY BE AN INDICATION OF DIRECT CYCLONE INTERACTION (DCI) WITH A
DEVELOPING TROPICAL DISTURBANCE (TD) TO THE SOUTH.
3. FORECAST REASONING.
   A. THE INITIAL PORTION OF THE FORECAST IS NOW ON A MORE WEST-
WARD TRAJECTORY THAN THE PREVIOUS FORECAST AND THE EXTENDED FORECAST
IS MORE TO THE RIGHT. HOWEVER, THE FUNDAMENTAL PHILOSOPHY OF THE
TRACK AND INTENSITY FORECASTS REMAINS THE SAME.
   B. TS 10W WILL CONTINUE TO TRACK GENERALLY NORTHWESTWARD ALONG THE
SOUTHWESTERN PERIPHERY OF A DEEP SUBTROPICAL RIDGE ENTRENCHED JUST
SOUTH OF MAINLAND JAPAN THROUGH TAU 72. OVER THIS PERIOD, THE SYSTEM
WILL INTENSIFY SLIGHTLY, PEAKING AT 60 KTS. THE INITIAL STORM MOTION
MAY BE SLOWED DOWN SLIGHTLY DUE TO DCI MENTIONED IN PARA 2.A.
   C. AFTER TAU 72, TS MALOU IS EXPECTED TO DRIFT INTO A WEAK
STEERING FLOW IN THE YELLOW SEA AS THE WESTERN EXTENT OF THE RIDGE
BREAKS DOWN IN RESPONSE TO A PASSING MID-LATITUDE TROUGH. IT WILL
THEN WEAKEN DUE TO THE COOLER WATERS OF THE NORTHERN YELLOW SEA AND
EXPOSURE TO WESTERLY VERTICAL WIND SHEAR ASSOCIATED WITH THE
BAROCLINIC ZONE. NUMERICAL MODEL GUIDANCE ARE IN FAIR AGREEMENT UP TO
TAU 24 THEN OFFER VARIOUS SOLUTIONS. GFS IS LEFT OF THE MODEL
ENVELOPE AND DEPICTS A LOOPING MOTION AFTER TAU 24, PRESUMABLY DUE TO
A MERGER BETWEEN THE SYSTEM AND THE AFOREMENTIONED TD. DUE TO THE
WEAK STEERING ENVIRONMENT IN THE YELLOW SEA, THE MODELS DIVERGE
SIGNIFICANTLY. ECMWF OPTS FOR AN ACCELERATED RECURVE ACROSS THE
KOREAN PENINSULA, NOGAPS BRINGS THE SYSTEM STRAIGHT INTO CHINA, AND
WBAR OFFERS AN ABBREVIATED RECURVE TOWARDS THE KOREAN STRAIT.
NEEDLESS TO SAY, ERRATIC STORM MOTION AFTER TAU 72 IS A DISTINCT
POSSIBILITY.//

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