Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Depression 16w Warning Nr 11//

From: SIU Weather Processor <[email-masked]>
Date: Sat, 23 Oct 2010 21:40:06 -0500

WDPN32 PGTW 240300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W WARNING NR 11//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL DEPRESSION (TD) 16W (SIXTEEN), LOCATED APPROXIMATELY
700 NM SOUTH-SOUTHEAST OF OKINAWA, JAPAN, HAS REMAINED QUASI-
STATIONARY OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS IMPROVED CONVECTIVE LOW LEVEL BANDING AROUND A
PARTIALLY EXPOSED, BROAD LOW LEVEL CIRCULATION (LLCC). ANIMATED
INFRARED SATELLITE IMAGERY DEPICTS FLARING DEEP CONVECTION ALONG THE
SOUTHERN PERIPHERY OF THE LOW LEVEL CIRCULATION CENTER (LLCC). THERE
IS UNCERTAINTLY IN THE INITIAL POSITION BASED ON THE PARTIALLY
EXPOSED LLCC IN A 232025Z TRMM MICROWAVE IMAGE AND MSI. THE INITIAL
INTENSITY IS SLIGHTLY HIGHER THAN THE PGTW AND RJTD DVORAK ESTIMATES
OF 25 KNOTS DUE TO AN EARLIER 231248Z ASCAT PASS DEPICTING 30 KNOT
WINDS ALONG THE SOUTHERN PERIPHERY. ENVIRONMENTAL ANALYSIS INDICATES
AN UPPER TROPOSPHERIC TROUGH TO THE NORTH IS INDUCING SUBSIDENCE
ALONG THE NORTHERN PERIPHERY OF THE LLCC, HINDERING POLEWARD
OUTFLOW, AND CAUSING INCREASED VERTICAL WIND SHEAR.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE IN FORECAST PHILOSOPHY SINCE
THE PREVIOUS BULLETIN.
   B. TD 16W IS CURRENTLY TRACKING ALONG THE SOUTHERN PERIPHERY OF A
LOW- TO MID-LEVEL SUBTROPICAL STEERING RIDGE. AN UPPER LEVEL, MID-
LATITUDE TROUGH CURRENTLY TRACKING OVER CHINA IS EXPECTED TO
CONTINUE TO DIG SOUTHWARD CAUSING THE STEERING RIDGE TO WEAKEN AND
REORIENT. THIS WILL ALLOW TD 16W TO TURN POLEWARD AROUND TAU 24.
ADDITIONALLY, POLEWARD OUTFLOW IS EXPECTED TO INCREASE INTO THE
UPPER LEVEL TROUGH AND SUPPORT CONSISTENT INTENSIFICATION.
   C. AFTER TAU 72, TD 16W IS FORECAST TO CONTINUE TRACKING
NORTHWARD ALONG A MID-LEVEL STEERING RIDGE. AROUND TAU 72, THE
INTENSIFICATION RATE SHOULD SLOW IN RESPONSE TO AN INCREASE IN
VERTICAL WIND SHEAR CAUSED BY A STRONG COLD SURGE ORIGINATING OVER
NORTHERN CHINA. THE AVAILABLE NUMERIC GUIDANCE IS SPREAD IN THE
POLEWARD TURN WITH NOGAPS, WBAR, UKMO FAVORING AN EARLIER POLEWARD
TURN, ALTHOUGH NOGAPS IMMEDIATELY PULLS THE SYSTEM NORTHWARD INTO
THE SUBTROPICAL RIDGE. ECMWF TURNS THE SYSTEM NORTHWARD TOWARD
OKINAWA, JAPAN. GFDN AND GFS ARE TRACKING TD 16W POLEWARD INITIALLY
AND THEN WESTWARD AFTER THE PASSAGE OF THE UPPER LEVEL TROUGH. JGSM
ERRONEOUSLY TRACKS IT CONSISTENTLY WESTWARD. THIS FORECAST IS IN
AGREEMENT WITH THE MODELS TRACKING MORE POLEWARD IN ANTICIPATION OF
AN APPROACHING MID-LATITUDE TROUGH DEEPENING AND REORIENTING THE
STEERING RIDGE.//

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