Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 16w Warning Nr 25//

From: SIU Weather Processor <[email-masked]>
Date: Wed, 27 Oct 2010 09:50:04 -0500

WDPN32 PGTW 271500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W WARNING NR 25//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 16W (CHABA), LOCATED APPROXIMATELY 240 NM SOUTH
OF KADENA AIR BASE, JAPAN, HAS TRACKED NORTHWARD AT 07 KNOTS OVER
THE PAST SIX HOURS. THE SYSTEM HAS STEADILY INTENSIFIED TO 110 KNOTS
AND IS NOW TRACKING POLEWARD ALONG THE WESTERN EXTENSION OF A DEEP
LAYER STEERING RIDGE TO THE EAST. A 12 NM EYE IS NOW VISIBLE IN
INFRARED SATELLITE IMAGERY. DUAL OUTFLOW CHANNELS HAVE SUPPORTED
INTENSIFICATION. POLEWARD OUTFLOW REMAINS PARTICULARLY VIGOROUS INTO
AN UPPER LEVEL LONGWAVE TROUGH OVER THE NORTH CENTRAL PACIFIC.
DVORAK ESTIMATES HAVE CLIMBED TO A 5.5 FROM RJTD AND 6.0 FROM PGTW,
INDICATING THE SYSTEM'S INITIAL INTENSITY NOW RANGES FROM 102 T0 115
KNOTS. THE SYNOPTIC SCALE COLD SURGE APPEARS TO HAVE HAD ALMOST NO
IMPACT ON INTENSIFICATION THUS FAR.
3. FORECAST REASONING.
   A. THE PREVIOUS TWO FORECASTS REMAIN CONSISTENT WITH ONE ANOTHER
AND CLOSE TO, BUT SLIGHTLY FASTER THAN, THE MODEL CONSENSUS,
ACCOUTING FOR THE TENDENCY OF THE CONSENSUS TO BE SLOW IN A
RECURVATURE SCENARIO. 120-HOUR FORECAST POSIT HAS BEEN DROPPED SINCE
THE SYSTEM WILL BE HUNDREDS OF NAUTICAL MILES DOWNSTREAM OF JAPAN
AND EXTRATROPICAL.
   B. THE SYSTEM IS FORECAST TO CONTINUE TO TRACK POLEWARD ALONG THE
WESTERN EDGE OF THE STEERING RIDGE TO THE EAST TOWARDS A TROUGH-
INDUCED WEAKNESS. THE SYSTEM WILL MAINTAIN ITS CURRENT INTENSITY FOR
THE NEXT 12 HOURS, IF NOT INTENSIFY SLIGHTLY, DUE TO SUSTAINED DUAL
OUTFLOW AND LOW TO MODERATE VERTICAL WIND SHEAR (VWS). AROUND TAU 36
VWS WILL ELEVATE AS THE SYSTEM APPROACHES A STRONG POLAR JET, WHICH
WILL RAPIDLY WEAKEN THE SYSTEM. THE SYSTEM WILL ALSO BEGIN TO
ACCELERATE NORTHEASTWARD AS IT CRESTS THE STEERING RIDGE, AND WILL
BEGIN EXTRATROPICAL TRANSITION AS IT INTERACTS WITH A BAROCLINIC
BOUNDARY RUNNING SOUTH OF JAPAN.
   C. 500 MB HEIGHT FIELDS SHOW CAPTURE OF THE SYSTEM BY THE TROUGH
AS EARLY AS 29/12Z, SUGGESTING THE SYSTEM COULD COMPLETE
EXTRATROPICAL TRANSITION FASTER THAN FORECAST. NONETHELESS, THE
TYPHOON IS STILL EXPECTED TO BE FULLY EXTRATROPICAL PRIOR TO PASSAGE
OVER THE KANTO REGION OF HONSHU. MODEL GUIDANCE DOES NOT SUPPORT RE-
INTENSIFICATION AS A BAROCLINIC SYSTEM AT THIS TIME.//

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