Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Depression 16w Warning Nr 03//

From: SIU Weather Processor <[email-masked]>
Date: Thu, 21 Oct 2010 22:15:16 -0500

WDPN32 PGTW 220300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W WARNING NR 03//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL DEPRESSION (TD) 16W, LOCATED APPROXIMATELY 470 NM
SOUTH-SOUTHWEST OF IWO TO, HAS TRACKED WESTWARD AT 09 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
DEPICTS A FULLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC)
WITH DISORGANIZED DEEP CONVECTION DISPLACED SOUTH OF THE
CENTER. UPPER LEVEL ANALYSIS INDICATES A MARGINAL ENVIRONMENT
WITH INCREASING 20-30 KNOT NORTHEASTERLY VERTICAL WIND
SHEAR (VWS) ASSOCIATED WITH THE TUTT CELL NEAR 18N 153E. THE
CURRENT INTENSITY IS BASED ON DVORAK ESTIMATES OF 25 KNOTS
FROM KNES AND PGTW. THERE IS FAIR CONFIDENCE IN THE CURRENT
POSITION BASED ON THE EXPOSED LLCC.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE IN THE FORECAST PHILOSOPHY
SINCE THE PREVIOUS BULLETIN. HOWEVER, THERE IS A HIGH DEGREE OF
UNCERTAINTY IN THE EXTENDED TRACK AND INTENSITY FORECAST.
   B.  TD 16W IS CURRENTLY TRACKING UNDER THE STEERING INFLUENCE
OF THE LOW-LEVEL SUBTROPICAL RIDGE POSITIONED TO THE NORTH. THE
SYSTEM IS EXPECTED TO TRACK WESTWARD THROUGH THE PERIOD WITH A
WEST-NORTHWESTWARD TRACK IN THE LATER TAUS.
TD 16W IS UNLIKELY TO RE-CURVE DUE TO A STRONG COLD SURGE AND LOW-
LEVEL HIGH EXPECTED BY ALL MODELS TO BUILD INTO THE EAST CHINA SEA
NEAR TAU 120. THE UNCERTAINTY IN THE EXTENDED TAUS IS BASED
PRIMARILY ON THE STRENGTH OF THE SYSTEM. IF THE SYSTEM REMAINS WEAK,
IT WILL TRACK MORE WESTWARD UNDER THE LOW-LEVEL FLOW. IF IT
STRENGTHEN TO 55-65 KNOTS, THE SYSTEM MAY TRACK NORTHWESTWARD UNTIL
IT ENCOUNTERS STRONG VERTICAL WIND SHEAR AND DE-COUPLES (THEN TRACKS
SOUTHWESTWARD UNDER LOW-LEVEL NORTHEASTERLIES ASSOCIATED WITH THE
COLD SURGE). MODEL GUIDANCE IS IN POOR AGREEMENT AND HAS BEEN
ERRATIC. THE DYNAMIC MODELS ARE EITHER RE-CURVING THE SYSTEM (ECMWF,
NOGAPS), RE-CURVING BUT DISSIPATING SOUTHEAST OF OKINAWA (GFS), OR
TRACKING THE SYSTEM WESTWARD (UKMO, JGSM, WBAR). TD 16W IS FORECAST
TO SLOWLY INTENSIFY THROUGH THE NEXT 36-48 HOURS DUE TO THE
UNFAVORABLE CONDITIONS.
   C. IN THE EXTENDED TAUS, MODEL GUIDANCE DIVERGES. THIS
FORECAST CONTINUES TO FAVOR A WEST-NORTHWESTWARD TO NORTHWESTWARD
TURN FOLLOWED BY DISSIPATION AND DE-COUPLING. MODEL GUIDANCE HAS
BEEN CONSISTENT WITH THE TIMING AND STRENGTH OF A STRONG COLD SURGE
AND THE NORTHEASTERLY SURGE. THIS COLD SURGE SHOULD LEAD TO VERY
STRONG VWS SOUTH OF JAPAN WHICH IS EXPECTED TO RAPIDLY WEAKEN THE
SYSTEM WELL SOUTH OF JAPAN.//

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