Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Storm 16w Warning Nr 15//

From: SIU Weather Processor <[email-masked]>
Date: Sun, 24 Oct 2010 21:30:05 -0500

WDPN32 PGTW 250300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W WARNING NR 15//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 16W (CHABA), LOCATED APPROXIMATELY 590 NM
SOUTH-SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED
NORTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY SHOWS IMPROVED DEEP CONVECTION
BANDING WITHIN THE PAST SIX HOURS ALONG THE SOUTHERN AND WESTERN
PERIPHERY OF THE LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL
POSITION IS BASED ON A 241929Z TRMM 36H MICROWAVE IMAGE, WHICH
DEPICTS A TIGHTLY WRAPPED LLCC. THE INITIAL INTENSITY IS BASED ON
PGTW, KNES, AND RJTD DVORAK ESTIMATES OF 45 KNOTS. ALTHOUGH
EQUATORWARD OUTFLOW HAS IMPROVED, AN UPPER TROPOSPHERIC TROUGH IS
LIMITING DEEP CONVECTION ALONG THE NORTHEASTERN SIDE OF THE LLCC AND
IS HINDERING POLEWARD OUTFLOW. TS 16W IS CURRENTLY TRACKING ALONG
THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL SUBTROPICAL STEERING
RIDGE. A 240000Z AND 241200Z UPPER AIR ANALYSES INDICATE A
MID-LATITUDE TROUGH IS TRACKING OVER NORTHEASTERN CHINA AND DIGGING
SOUTHEASTWARD.
3. FORECAST REASONING.
   A. THE FORECAST INTENSITIES HAVE INCREASED DUE TO CURRENT
INTENSIFICATION TRENDS, MODEL GUIDANCE, AND IMPROVED OUTFLOW.
   B. THE STEERING RIDGE IS FORECAST TO CONTINUE TO RE-ORIENT AND
WEAKEN WITH THE PASSING MID-LATITUDE TROUGH, ALLOWING TS 16W TO TURN
MORE POLEWARD OVER THE NEXT 36 HOURS. INCREASED POLEWARD OUTFLOW
INTO THE TROUGH AND GOOD EQUATORWARD OUTFLOW SHOULD SUPPORT FURTHER
INTENSIFICATION.
   C. AFTER TAU 72, TS CHABA IS EXPECTED TO CONTINUE TRACKING
NORTHWARD AND AROUND TAU 96, TURN NORTHEASTWARD AS IT ROUNDS THE
SUBTROPICAL RIDGE AXIS. AT THIS TIME, INCREASED VERTICAL WIND SHEAR
ASSOCIATED WITH THE MID-LATITUDE WESTERLIES AS WELL AS LOWER OCEAN
HEAT CONTENT SHOULD INITIALLY WEAKEN TS 16W AS IT BEGINS
EXTRATROPICAL TRANSITION. NUMERICAL MODEL GUIDANCE IS SPREAD IN THE
TIMING OF THE TURN NORTHWARD AND THEN NORTHEASTWARD, EXCEPT FOR GFDN
WHICH ERRONEOUSLY INTENSIFIES TS 16W AND TRACKS IT WESTWARD. THE
MAJORITY OF THE MODELS ARE INDICATING A NORTHWARD TURN WITH NOGAPS
AND GFS TURNING THE SYSTEM LATEST AND THEN TRACKING THE SYSTEM
TOWARD OKINAWA. THE ECMWF, WBAR, AND UKMO MODELS TURN THE SYSTEM
NORTHEASTWARD MORE SHARPLY SOUTH OF OKINAWA, INDICATING THE
APPROACHING MID-LATITUDE TROUGH WILL DEEPEN ENOUGH TO INDUCE A
RECURVATURE SCENARIO. THIS FORECAST IS IN AGREEMENT WITH THE
FASTER TURN NORTHEASTWARD IN ANTICIPATION OF A DEEPER MID-LATITUDE
TROUGH AND IS RIGHT OF MODEL CONSENSUS TO ACCOUNT FOR THE GFDN
WESTWARD TRACK ERROR.//

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