Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Depression 16w (sixteen)

From: SIU Weather Processor <[email-masked]>
Date: Thu, 21 Oct 2010 10:49:06 -0500

WDPN32 PGTW 211500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (SIXTEEN)
WARNING NR 01//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
    A. TROPICAL DEPRESSION (TD) 16W (SIXTEEN), LOCATED APPROXIMATELY
460 NM SOUTH OF IWO TO, HAS TRACKED NORTHWESTWARD AT 04 KNOTS OVER
THE PAST SIX HOURS. THE DISTURBANCE HAS MIGRATED BENEATH AN UPPER
LEVEL RIDGE EXTENSION OVER THE PAST SIX HOURS, BUFFERING IT FROM
MODERATE NORTHERLY VERTICAL WIND SHEAR AND ALLOWING DEEP CONVECTION
TO BUILD IN OVER THE LOW LEVEL CIRCULATION CENTER (LLCC). PREVIOUSLY
CONVECTION HAD BEEN INHIBITED BY AN ENCROACHING TROPICAL UPPER LEVEL
TROPOSPHERIC TROUGH THAT HAD DUG TO THE NORTH OF THE SYSTEM.
CURRENTLY THE SYSTEM IS ASSESSED AT 25 KNOTS, MEETING JTWC WARNING
CRITERIA FOR SYSTEMS IN THE NORTHWESTERN PACIFIC. DVORAKS FROM PGTW
AND RJTD RANGE FROM 1.5 TO 2.0 OR 25 TO 30 KNOTS. A 210814Z WINDSAT
IMAGE SHOWS A WELL-DEFINED CIRCULATION CENTER WITH WINDS AS HIGH AS
20 KNOTS. SINCE THEN DEEP CONVECTION HAS BUILT OVER THE CENTER,
WHICH HAS LIKELY INCREASED THE INTENSITY OF THE LLCC TO 25 KNOTS.
BANDING FEATURES ARE STILL RELATIVELY IMMATURE AND BEST DEFINED IN
THE LOWER LEVELS AS HIGHLIGHTED IN A 211228Z TMI 37H MICROWAVE
IMAGE. THE HIGHER FREQUENCY IMAGE SHOWS THAT THE LLCC IS STILL
BIASED TOWARDS THE NORTH OF THE BUILDING CONVECTION.
3. FORECAST REASONING.
    A. THIS MESSAGE ESTABLISHES THE FORECAST REASONING FOR THIS
SYSTEM.
    B. TS 16W WILL TRACK UNDER THE INFLUENCE OF STRONG LOW TO MID-
LEVEL RIDGING TO THE NORTH. THE SYSTEM WILL SLOWLY INTENSIFY UNDER
THE PROTECTION OF THE UPPER LEVEL RIDGE AXIS, BENEFITING FROM LOW
VERTICAL WIND SHEAR AND FAVORABLE WESTWARD VENTING INTO AN UPPER
LEVEL INVERTED TROUGH OVER THE PHILIPPINE SEA. IT IS POSSIBLE FOR
THE SYSTEM TO INTENSIFY FASTER THAN FORECAST IF THIS TROUGH PULLS
NORTH, WHICH WOULD IMPROVE OUTFLOW.
    C. AROUND TAU 72 A MID TO DEEP LAYER TROUGH WILL ERODE THE
STEERING RIDGE TO THE NORTH AND DRAW THE SYSTEM POLEWARD. MODEL
GUIDANCE ALL SUGGEST OR HINT AT A BREAK IN THE STEERING RIDGE WITH
NOGAPS OVERDEEPENING A LONGWAVE TROUGH, WHICH IS RESPONSIBLE FOR THE
EROSION OF THE STEERING RIDGE, AND PULLS THE SYSTEM NORTH DAYS AHEAD
OF THE OTHER TRACKERS. ECMWF RESOLVES A WEAKER SYSTEM AND CONTINUES
TO TRACK THE SYSTEM WEST UNDER THE INFLUENCE OF THE LOW LEVEL
EASTERLY FLOW. THE OFFICIAL FORECAST LIES CLOSE TO THE MODEL
CONSENSUS, WHICH ACCOUNTS FOR THE PREMATURE RECURVATURE OF NOGAPS
AND THE NEAR WESTWARD STRAIGHT-RUNNING ECMWF SOLUTION.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
To unsubscribe from WX-TROPL send e-mail to [email-masked] with
"unsub wx-tropl" in the body of your message. For help with WX-TROPL
write to [email-masked]. For more information on tropical weather products, see the NHC Homepage at http://www.nhc.noaa.gov.