Tropical Depression SEVENTEEN-E

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TROPICAL DEPRESSION SEVENTEEN-E DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP172008
200 PM PDT THU OCT 23 2008
 
DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB WERE 35 KT AT
1800 UTC...HOWEVER 25 KM ASCAT WIND RETRIEVALS IN A PASS FROM 1700
UTC SHOWED ONLY A COUPLE OF AMBIGUITIES WITH WIND SPEEDS OF 25 TO
30 KT.  BASED ON THE ASCAT DATA AND THE FACT THAT THE SURFACE
CENTER STILL APPEARS TO BE DISPLACED SOUTHEAST OF THE DEEP
CONVECTION...THE INITIAL INTENSITY IS KEPT AT 30 KT FOR THIS CYCLE.
 
THE FORECAST REASONING REMAINS UNCHANGED...WITH THE SYSTEM EXPECTED
TO ENCOUNTER INCREASING VERTICAL SHEAR BY EARLY FRIDAY...LEADING TO
THE DECOUPLING OF THE SURFACE AND MID-LEVEL CIRCULATIONS.  THIS
REASONING IS IN BEST AGREEMENT WITH THE 1200 UTC RUNS OF THE UKMET
AND ECMWF GLOBAL MODELS...WHICH BOTH SHOW THE MID-LEVEL CIRCULATION
CONTINUING NORTHWARD TOWARD THE COAST OF MEXICO AS THE LOW-LEVEL
CIRCULATION TURNS TOWARD THE WEST TO THE SOUTH OF A LOW-LEVEL RIDGE
OVER THE EASTERN PACIFIC.  THE CURRENT FORECAST TRACK IS
ESSENTIALLY AN UPDATE OF THE PREVIOUS ADVISORY.
 
WITH THE SHEAR POISED TO INCREASE SOON...THE DEPRESSION CONTINUES TO
HAVE A EVER SHRINKING WINDOW OF OPPORTUNITY TO REACH TROPICAL STORM
STATUS.  THE OFFICIAL FORECAST SHOWS A PEAK INTENSITY OF 35 KT AT
12 HOURS...IN AGREEMENT WITH THE SHIPS MODEL.  AFTER THAT TIME...
WEAKENING IS FORECAST AS THE VERTICAL SHEAR INCREASES ABOVE 40 KT
AFTER 36 HOURS.  A GRADUAL SPIN DOWN TO A REMNANT LOW IS EXPECTED
BY 72 HOURS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      23/2100Z 13.9N 104.9W    30 KT
 12HR VT     24/0600Z 14.6N 104.9W    35 KT
 24HR VT     24/1800Z 15.8N 105.2W    30 KT
 36HR VT     25/0600Z 16.7N 105.9W    30 KT
 48HR VT     25/1800Z 17.3N 107.1W    25 KT
 72HR VT     26/1800Z 17.5N 110.0W    20 KT...REMNANT LOW
 96HR VT     27/1800Z 17.5N 113.0W    20 KT...REMNANT LOW
120HR VT     28/1800Z...DISSIPATED
 
$$
FORECASTER BRENNAN/BEVEN
 
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