Tropical Depression EIGHTEEN-E

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TROPICAL DEPRESSION EIGHTEEN-E DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP182006
200 AM PDT FRI OCT 27 2006
 
IF THE DEPRESSION STILL HAS A WELL-DEFINED SURFACE CIRCULATION
CENTER...YOU WOULD NEVER KNOW IT FROM THE QUIKSCAT AMBIGUITIES AT
0144Z. THIS PASS SHOWED A LOT OF LIGHT WINDS...A SHARP NORTH-SOUTH
TROUGH AXIS...AND PRECIOUS LITTLE ELSE. AN SSMIS MICROWAVE PASS AT
0305Z SHOWED ALMOST NO STRUCTURE IN THE LOW CLOUD LINES. HOWEVER...
THERE DOES APPEAR TO BE ROTATION ALOFT AROUND THE LIMITED DEEP
CONVECTION...SO IF THE CONVECTION SHOULD INCREASE A SURFACE
CIRCULATION COULD BECOME BETTER DEFINED AGAIN.  THE INITIAL
INTENSITY OF THE CYCLONE REMAINS SUB-ROSA...AND IS LOWERED TO 25 KT
IN ACCORD WITH THE QUIKSCAT DATA.

THE INITIAL MOTION IS HARD TO GAUGE.  WHILE THERE ARE HINTS THAT
WHATEVER SURFACE CENTER EXISTS MAY BE LAGGING BEHIND THE DEEP
CONVECTION...I'LL GO WITH CONTINUITY AND THE ROTATION ALOFT FOR AN
INITIAL MOTION ESTIMATE OF 265/8.  THE LATEST RUNS OF THE GLOBAL
MODELS CONTINUE TO INDICATE THAT MID-LEVEL RIDGING WILL BUILD TO THE
NORTH AND NORTHWEST OF THE DEPRESSION...WHICH WOULD TAKE THE SYSTEM
ON A TRACK A LITTLE SOUTH OF WEST.  THE OFFICIAL FORECAST IS
ADJUSTED JUST A LITTLE SOUTH OF THE PREVIOUS TRACK...AND IS IN GOOD
AGREEMENT WITH THE GFDL AND MEDIUM BAM GUIDANCE.
 
WITH LIMITED CONVECTION AND POOR DEFINITION OF THE WIND FIELD...THE
DEPRESSION IS BECOMING A CANDIDATE FOR EARLY DISSIPATION.
HOWEVER...BOTH THE SHIPS AND GFDL GUIDANCE SUGGEST MODEST
STRENGTHENING OVER THE NEXT COUPLE OF DAYS AND THE OFFICIAL
FORECAST...FOR NOW...WILL INDICATE THE SAME. FACTORS FAVORING THIS
SCENARIO INCLUDE LIGHT SHEAR AND VERY WARM WATERS. ON THE OTHER
HAND...THE UPPER-LEVEL OUTFLOW IS NOT WELL ESTABLISHED AND THE
ENVIRONMENT IS A LITTLE DRY...AND IF THESE FACTORS KEEP A LID ON
THE CONVECTION OVER THE NEXT DAY OR SO THEN THE DEPRESSION COULD
DISSIPATE.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/0900Z 16.6N 106.4W    25 KT
 12HR VT     27/1800Z 16.4N 107.7W    30 KT
 24HR VT     28/0600Z 16.0N 109.5W    35 KT
 36HR VT     28/1800Z 15.7N 111.5W    45 KT
 48HR VT     29/0600Z 15.5N 113.6W    45 KT
 72HR VT     30/0600Z 15.5N 117.5W    45 KT
 96HR VT     31/0600Z 15.5N 121.5W    40 KT
120HR VT     01/0600Z 15.5N 125.5W    40 KT
 
$$
FORECASTER FRANKLIN
 
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