Tropical Depression THIRTEEN-E

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TROPICAL DEPRESSION THIRTEEN-E DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2 AM PDT SAT SEP 11 2004
 
THE DVORAK T NUMBER FROM TAFB IS 3.0 BASED ON THE 0600Z GOES-10
IMAGE...AND FOLLOWING THE GOES-12 ECLIPSE PERIOD...SAB OBTAINED A
DVORAK T NUMBER OF 2.5 FROM THE 0645Z IMAGE.  WHILE THESE ESTIMATES
COULD BE GROUNDS FOR UPGRADING THE DEPRESSION TO A TROPICAL
STORM...WE PREFER TO WAIT TO SEE IF THE CONVECTIVE BURST THAT BEGAN
DURING THE GOES-12 ECLIPSE PERSISTS...AND PERHAPS WAIT FOR VISIBLE
IMAGERY LATER THIS MORNING TO BE MORE CONFIDENT THAT THE LOW LEVEL
CENTER IS SUFFICIENTLY INVOLVED WITH THE CONVECTION.  SHORTWAVE IR
IMAGERY SUGGESTS THE CENTER IS JUST BARELY TUCKED INTO THE
NORTHEASTERN PORTION OF THE CONVECTION...INDICATIVE OF THE MODERATE
EASTERLY SHEAR OVER THE SYSTEM.
 
THE INITIAL MOTION ESTIMATE IS 280/12...OR JUST NORTH OF
WEST...ALONG THE SOUTHERN PERIPHERY OF THE MID/UPPER LEVEL RIDGE
CENTERED OVER NORTHERN MEXICO. THE NOGAPS AND GFDN IGNORE THE
INITIAL MOTION AND IMMEDIATELY TAKE THE SYSTEM TOWARD THE NORTH OR
NORTHWEST...AND THESE SOLUTIONS ARE DISCOUNTED THROUGHOUT THE
FORECAST PERIOD. THE INITIAL MOTION IS EXPECTED TO GENERALLY
CONTINUE FOR ABOUT THE NEXT 36 HOURS OR SO...AS AGREED UPON BY THE
GFS...GFDL...AND UKMET MODELS. BEYOND 36 HOURS...THE OFFICIAL
FORECAST STILL RELIES ON A CONSENSUS OF THESE THREE MODELS...ALL OF
WHICH FORECAST THE RIDGE TO THE NORTH TO WEAKEN AND FOR THE
TROPICAL CYCLONE TO SLOW DOWN AND TURN TOWARD THE NORTHWEST OR
NORTH. HOWEVER...WE ARE NOT READY TO FOLLOW A NORTHWARD TURN AS
ABRUPT AS THAT SHOWN BY THE GFS AND GFDL...AND RATHER STAY CLOSER
TO THE MORE GRADUAL TURN IN THE UKMET. THE OFFICIAL FORECAST IS
FASTER THAN THE PREVIOUS ADVISORY AND IS MORE TO THE RIGHT BEYOND
DAY THREE...AND NOW INCLUDES A NORTH-NORTHWEST MOTION ON DAYS FOUR
AND FIVE.

ON THE NEW FORECAST TRACK...SEA SURFACE TEMPERATURES SHOULD REMAIN
28-29C AND THE VERTICAL SHEAR WEAK TO MODERATE IN STRENGTH. THE
INTENSITY FORECAST IS JUST AN UPDATE TO THE PREVIOUS
ADVISORY...REACHING HURRICANE STRENGTH IN 48 HOURS AND LEVELLING
OFF THE INTENSITY AT 75 KNOTS AT DAYS 4 AND 5...GENERALLY IN GOOD
AGREEMENT WITH SHIPS.
 
FORECASTER KNABB/JARVINEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      11/0900Z 11.7N  97.1W    30 KT
 12HR VT     11/1800Z 12.0N  98.8W    40 KT
 24HR VT     12/0600Z 12.4N 100.8W    45 KT
 36HR VT     12/1800Z 12.7N 102.1W    55 KT
 48HR VT     13/0600Z 13.2N 103.1W    65 KT
 72HR VT     14/0600Z 15.0N 104.5W    70 KT
 96HR VT     15/0600Z 16.5N 105.5W    75 KT
120HR VT     16/0600Z 18.0N 106.0W    75 KT
 
 
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