[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 210853
TCDAT3
TROPICAL STORM LISA DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT TUE SEP 21 2004

LISA CONTINUES UNDER NORTHERLY SHEAR CAUSED BY THE OUTFLOW FROM
KARL..WITH THE CENTER IN THE NORTHERN SIDE OF THE VERY COLD
CONVECTIVE MASS.  SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM
SAB...AND 45 KT FROM TAFB AND AFWA.  THE INITIAL INTENSITY REMAINS
50 KT FOR THIS ADVISORY...AND THIS MIGHT BE A LITTLE CONSERVATIVE.

THE INITIAL MOTION IS 280/10.  LISA IS EMBEDDED IN A TROUGH
EXTENDING FROM HURRICANE KARL THROUGH LISA TO A DISTURBANCE
CENTERED NEAR 9.5N31W.  EASTERLY LOW-LEVEL FLOW IS SEEN NORTHEAST
OF THE TROUGH AXIS AND WEST TO NORTHWEST FLOW SOUTHWEST OF IT.
THERE SEEM TO BE THREE POTENTIAL TRACK OPTIONS FOR LISA.  FIRST...A
CONTINUATION OF THE CURRENT WESTWARD MOTION AS KARL MOVES AWAY AND
RIDGING DEVELOPS NORTH OF LISA.  THIS IS FAVORED BY THE NHC98.
SECOND...A TURN TO THE NORTHWEST AND NORTH IN THE WAKE OF KARL.
THIS IS SUPPORTED BY THE NOGAPS AND THE UKMET.  FINALLY...A TURN TO
THE SOUTHWEST AS THE DISTURBANCE TO THE SOUTHEAST DEVELOPS.  THIS
IS SUPPORTED BY THE GFDL.  THE TRACK FORECAST WILL FOLLOW THE
PREVIOUS WESTWARD MOTION AS THERE IS CURRENTLY NO OBVIOUS SIGN THAT
EITHER OF THE OTHER SCENARIOS ARE BEGINNING.  ONE SMALL CHANGE IS
TO INTRODUCE A NORTHWESTERLY MOTION AFTER 96 HR...AS LISA WOULD BE
APPROACHING A WEAKNESS IN THE RIDGE TO THE NORTH BY THAT TIME.
THIS IS ANOTHER LOW CONFIDENCE FORECAST.

THE INTENSITY FORECAST IS EVEN LOWER CONFIDENCE.  LISA IS A SMALL
SYSTEM BETWEEN TWO LARGER ONES...AND THERE IS A CHANCE THAT IT
COULD GET SWALLOWED...PARTICULARLY BY THE DISTURBANCE TO THE
SOUTHEAST.  IF THAT DOES NOT HAPPEN... LARGE-SCALE MODELS ALL
FORECAST SIGNIFICANT NORTHEASTERLY SHEAR ALONG THE FORECAST TRACK
IN 48-72 HR...WHICH COULD CONSIDERABLY DAMAGE LISA.  THE SHIPS AND
GFDL BOTH SLOWLY STRENGTHEN LISA IN SPITE OF THE SHEAR...AND THE
OFFICIAL FORECAST FOLLOWS THE SHIPS GUIDANCE.  HOWEVER...THERE IS A
CHANCE LISA MIGHT NOT SURVIVE FOR 120 HR.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL      21/0900Z 14.0N  38.9W    50 KT
 12HR VT     21/1800Z 14.3N  40.3W    50 KT
 24HR VT     22/0600Z 14.9N  42.0W    50 KT
 36HR VT     22/1800Z 15.4N  43.6W    50 KT
 48HR VT     23/0600Z 15.8N  45.2W    55 KT
 72HR VT     24/0600Z 16.0N  47.5W    60 KT
 96HR VT     25/0600Z 16.1N  50.0W    65 KT
120HR VT     26/0600Z 17.5N  51.5W    65 KT


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