Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Storm 12w Warning Nr 04//

From: SIU Weather Processor <[email-masked]>
Date: Wed, 15 Sep 2010 09:27:18 -0500

WDPN31 PGTW 151500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W WARNING NR 04//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 12W (FANAPI), LOCATED APPROXIMATELY
335 NM SOUTH OF OKINAWA, JAPAN HAS TRACKED NORTHWESTWARD AT 03 KNOTS
OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY AND A
151009Z SSMIS 91 GHZ MICROWAVE IMAGE DEPICT TIGHTLY CURVED
CONVECTIVE BANDING WRAPPING IN FROM ALL QUADRANTS WITH DEEP
CONVECTION BUILDING OVER THE SYSTEM CENTER. OVER THE PAST SIX HOURS
THE SYSTEM HAS SLOWED CONSIDERABLY DUE TO A WEAKENING STEERING
ENVIRONMENT. THE CURRENT POSITION IS BASED ON THE AFOREMENTIONED
MICROWAVE PASS WITH FAIR CONFIDENCE. THE CURRENT INTENSITY IS BASED
ON DVORAK ESTIMATES FROM PGTW, KNES, AND PGTW OF 35 KNOTS. UPPER
LEVEL ANALYSIS REVEALS TS 12W IS EXPERIENCING IMPROVED EQUATORWARD
OUTFLOW ASSOCIATED WITH THE TROPICAL UPPER TROPOSPHERIC TROUGH
(TUTT) CELL APPROACHING FROM THE EAST AND A TUTT CELL MOVING AWAY
FROM THE SYSTEM TO THE WEST. ANIMATED WATER VAPOR IMAGERY INDICATES
AN APPROACHING MID-LATITUDE UPPER LEVEL TROUGH MAY BE STARTING TO
ENHANCE POLEWARD OUTFLOW. OVERALL THE SYSTEM IS IN A FAVORABLE
ENVIRONMENT FOR DEVELOPMENT WITH AN ANTICYCLONE OVER THE SYSTEM
CENTER, LOW VERTICAL WIND SHEAR, AND HIGH SEA SURFACE TEMPERATURES.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE FROM THE PREVIOUS PROGNOSTIC
REASONING MESSAGE.
   B. TS 12W IS CURRENTLY TRACKING ALONG THE SOUTHWESTERN PERIPHERY
OF A LOW TO MID-LEVEL STEERING RIDGE ANCHORED SOUTH OF JAPAN. NEAR
TAU 12, A MID-LATITUDE TROUGH IS FORECAST TO WEAKEN THE STEERING
RIDGE CAUSING THE SYSTEM TO SLOW AND TRACK POLEWARD. WITHIN THIS
WEAKENED STEERING ENVIRONMENT, TS 12W IS EXPECTED TO INTENSIFY AS
POLEWARD OUTFLOW IS ENHANCED BY THE MID-LATITUDE WESTERLY FLOW
DIGGING DOWN TOWARD THE SYSTEM, AND EQUATORWARD OUTFLOW CONTINUES TO
IMPROVE DUE TO THE TUTT CELL TO THE EAST. AFTER TAU 48 THE SYSTEM IS
EXPECTED TO TURN BACK TOWARD THE NORTHWEST AS THE SUBTROPICAL RIDGE
BUILDS BACK IN NORTH OF THE SYSTEM.
   C. BY TAU 72, TS 12W IS FORECAST TO CONTINUE TRACKING
NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE REBUILDING
SUBTROPICAL RIDGE EXTENDING INTO EASTERN CHINA. THE SYSTEM IS
FORECAST TO CONTINUE INTENSIFYING THROUGHOUT THE FORECAST PERIOD DUE
TO FAVORABLE ENVIRONMENTAL CONDITIONS. NUMERICAL MODEL GUIDANCE
REMAINS IN GOOD AGREEMENT WITH THE OVERALL TRACK PHILOSOPHY, BUT
CONTINUES TO DEPICT UNCERTAINTY WITH THE TIMING OF THE TURN BACK TO
THE NORTHWEST. GFDN AND GFS DEPICT A SLOWER TURN, WHILE ECMWF AND
NOGAPS DEPICT A MORE RAPID TURN. THIS FORECAST FAVORS A QUICKER TURN
BACK TO THE NORTHWEST AND IS CLOSE TO MODEL CONSENSUS.//

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