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Tropical Depression SIXTEEN (Text)

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TROPICAL DEPRESSION SIXTEEN DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL162007
500 AM EDT SUN OCT 28 2007
 
THE CENTER OF THE DEPRESSION IS DIFFICULT TO IDENTIFY ON INFRARED OR
NIGHT-VIS IMAGERY.  RECENT MICROWAVE PASSES ALSO ARE NOT
CONCLUSIVE...BUT SUGGEST THAT THE DEPRESSION IS CONTINUING ON ITS
PREVIOUS TRACK...WITH AN INITIAL MOTION ESTIMATE OF 300/6.  DEEP
CONVECTION NEAR THE CENTER LACKS ANY APPRECIABLE BANDING...AND A
RECENT ASCAT PASS DOES NOT INDICATE THAT ANY STRENGTHENING HAS
OCCURRED.  WITH AN UPPER-LEVEL LOW IMPARTING WESTERLY SHEAR OVER THE
CYCLONE...THE ENVIRONMENT DOES NOT FAVOR MUCH DEVELOPMENT IN THE
SHORT TERM.  GLOBAL MODELS SUGGEST THAT THE UPPER LOW WILL WASH OUT
IN A COUPLE OF DAYS...LEAVING THE CYCLONE UNDER A LESS HOSTILE
UPPER PATTERN...BUT THE ENVIRONMENT NEVER APPEARS TO BE IDEAL FOR
DEVELOPMENT.  IN ADDITION...THERE IS AMPLE OPPORTUNITY FOR LAND
INTERACTIONS OVER THE NEXT FEW DAYS THAT WOULD HINDER
STRENGTHENING.  THE GFDL AND HWRF INTENSITY FORECASTS...WHICH
SUGGEST A MORE VERTICALLY-CONNECTED CYCLONE THAN APPEARS TO
EXIST...ARE LARGELY BEING DISCOUNTED.  THE OFFICIAL FORECAST IS IN
GOOD AGREEMENT WITH THE LGEM.

TRACK FORECASTING OF WEAK SYSTEMS IN SHEARED ENVIRONMENTS IS
PARTICULARLY CHALLENGING...AND THE AVAILABLE MODEL GUIDANCE
REFLECTS THIS UNCERTAINTY.  THE PRIMARY SYNOPTIC PLAYERS ARE THE
UPPER-LOW ALREADY MENTIONED...A MID-LEVEL RIDGE OVER THE
SOUTHWESTERN ATLANTIC...A BROAD LOW-LEVEL CYCLONIC ENVELOPE
SURROUNDING THE DEPRESSION...AND A MID- TO UPPER-LEVEL SHORTWAVE
TROUGH FORECAST TO MOVE INTO THE SOUTHEASTERN UNITED STATES IN ABOUT
FOUR DAYS.  THE GFDL AND HWRF LIE ON THE EASTERN EDGE OF THE
GUIDANCE ENVELOPE...TAKING THE CYCLONE ACROSS HISPANIOLA AND
THROUGH THE CENTRAL BAHAMAS IN 2-3 DAYS.  THIS APPEARS TO RESULT
FROM AN OVERLY STRONG INTERACTION WITH THE UPPER LOW.  ANOTHER
SCENARIO IS FOR THE DEPRESSION TO TURN TEMPORARILY TO THE NORTHWEST
IN RESPONSE TO THE UPPER-LOW...BUT THEN BEND BACK TO THE
WEST-NORTHWEST IN A COUPLE DAYS AROUND THE BROAD LOW-LEVEL
GYRE...BEFORE BEING DEFLECTED NORTHEASTWARD WHEN THE SHORT WAVE
ARRIVES ON DAYS 4-5.  THIS IS THE SOLUTION OF THE UKMET.  ON THE
LEFT SIDE OF THE GUIDANCE ENVELOPE ARE THE BAM MODELS AND THE
GFS...WHICH TAKE A RELATIVELY WEAK AND ILL-DEFINED LOW
WEST-NORTHWESTWARD UNTIL THE MID-LATITUDE SHORT WAVE ARRIVES AND
SLOWLY RECURVES THE CYCLONE.  THIS IS THE SOLUTION FAVORED BY THE
OFFICIAL FORECAST.  IT IS WORTH REITERATING THAT THE UNCERTAINTY
LEVEL IS HIGH.
 

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      28/0900Z 16.2N  72.1W    30 KT
 12HR VT     28/1800Z 17.0N  73.2W    30 KT
 24HR VT     29/0600Z 17.9N  74.6W    35 KT
 36HR VT     29/1800Z 18.9N  76.3W    35 KT
 48HR VT     30/0600Z 19.7N  77.7W    40 KT
 72HR VT     31/0600Z 21.5N  80.0W    50 KT
 96HR VT     01/0600Z 23.0N  79.0W    40 KT
120HR VT     02/0600Z 25.0N  77.0W    45 KT...EXTRATROPICAL
 
$$
FORECASTER FRANKLIN
 
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