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Tropical Storm ANDRES


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TROPICAL STORM ANDRES DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP022009
200 AM PDT MON JUN 22 2009

ENHANCED INFRARED SATELLITE IMAGES SHOW VERY COLD CLOUD TOPS...WITH
SOME BANDING FEATURES OVER THE SOUTHERN AND WESTERN SEMICIRCLES OF
THE TROPICAL STORM.  CURRENT INTENSITY IS SET AT 45 KT IN
ACCORDANCE WITH THE LATEST DVORAK ESTIMATE FROM TAFB.  THIS IS ALSO
IN AGREEMENT WITH A QUIKSCAT PASS FROM SEVERAL HOURS AGO WHICH
SHOWED AT LEAST ONE BELIEVABLE WIND VECTOR IN THE 40 TO 45 KT
RANGE.  ANDRES IS EXPECTED TO REMAIN OVER VERY WARM WATER FOR AT
LEAST THE NEXT 36 HOURS...HOWEVER THE SHIPS MODEL PROJECTS 20 TO 25
KT OF EAST-NORTHEASTERLY SHEAR TO AFFECT THE TROPICAL CYCLONE
WITHIN THE NEXT DAY OR SO.  IT SHOULD BE NOTED THAT THE SHIPS
OUTPUT SHOWS THAT THIS DIRECTION OF THE VERTICAL SHEAR VECTOR IS
LESS UNFAVORABLE THAN SHEAR FROM SOME OTHER DIRECTIONS.  GIVEN THIS
AND OTHER FAVORABLE ENVIRONMENTAL FACTORS SUCH AS ABUNDANT LOW- TO
MID-LEVEL MOISTURE AND AN ENVIRONMENT OF LOW-LEVEL CYCLONIC
VORTICITY...BOTH THE SHIPS AND LGEM PREDICT THAT ANDRES WILL BECOME
A HURRICANE IN 24 TO 36 HOURS.  THE OFFICIAL FORECAST FOLLOWS SUIT. 
LATER IN THE FORECAST PERIOD...INCREASINGLY LESS CONDUCIVE
ATMOSPHERIC AND OCEANIC CONDITIONS SHOULD INDUCE WEAKENING.

INITIAL MOTION IS A SOMEWHAT UNCERTAIN 300/3 AS THE CENTER IS
DIFFICULT TO TRACK USING NIGHTTIME SATELLITE IMAGES.  THE TRACK
FORECAST CONTINUES TO PRESENT A CHALLENGE.  MUCH OF THE DYNAMICAL
MODEL GUIDANCE SHOW ANDRES MOVING NEAR OR OVER THE SOUTHWEST COAST
OF MEXICO.  THIS MOTION WOULD APPARENTLY BE THE RESULT OF ANDRES
ROTATING AROUND THE EASTERN SIDE OF A BROAD LOW-LEVEL CYCLONIC GYRE
WITHIN WHICH IT IS EMBEDDED.  HOWEVER THE DYNAMICAL MODEL FORECASTS
ALSO SHOW PRONOUNCED MID- TO UPPER- TROPOSPHERIC RIDGING OVER
MEXICO...WHICH WOULD TEND TO DRIVE THE TROPICAL CYCLONE ON A MORE
WESTWARD TRACK...OR AT LEAST PARALLEL TO THE COAST.  THE OFFICIAL
FORECAST IS NUDGED A LITTLE TO THE RIGHT OF THE PREVIOUS ONE BUT
STILL LIES TO THE LEFT OF THE MODEL CONSENSUS.  IN 4 TO 5 DAYS IT
IS LIKELY THAT ANDRES WILL BE A WEAKENING SYSTEM BEING STEERED
MAINLY BY THE LOWER-LEVEL FLOW.

ALTHOUGH THE OFFICIAL FORECAST TRACK STILL DOES NOT EXPLICITLY
INDICATE LANDFALL...IT IS NONETHELESS CLOSE ENOUGH TO THE COAST SO
THAT A TROPICAL STORM WARNING MAY BE REQUIRED FOR A PORTION OF THE
SOUTHWEST COAST OF MEXICO LATER TODAY.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      22/0900Z 15.0N 102.1W    45 KT
 12HR VT     22/1800Z 15.6N 102.6W    55 KT
 24HR VT     23/0600Z 16.5N 103.3W    60 KT
 36HR VT     23/1800Z 17.6N 104.1W    65 KT
 48HR VT     24/0600Z 19.0N 105.6W    65 KT
 72HR VT     25/0600Z 21.0N 108.5W    55 KT
 96HR VT     26/0600Z 21.5N 112.5W    40 KT
120HR VT     27/0600Z 21.5N 117.0W    25 KT
 
$$
FORECASTER PASCH
 
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