000
WTNT44 KNHC 221437
TCDAT4
TROPICAL STORM LISA DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142010
1100 AM EDT WED SEP 22 2010
 
LISA IS PRODUCING A SMALL AREA OF DEEP CONVECTION NEAR THE SURFACE
CENTER...BUT MUCH OF THE LOW-LEVEL CIRCULATION IS EXPOSED AROUND
THE CONVECTIVE MASS.  DVORAK CURRENT INTENSITY ESTIMATES ARE 3.0/45
KT AND 2.5/35 KT FROM TAFB AND SAB...SO THE INITIAL INTENSITY IS
BEING MAINTAINED AT 40 KT.  A FEW MICROWAVE PASSES...PARTICULARLY A
0919 UTC SSMIS PASS...INDICATED THAT THE CENTER OF LISA HAS DRIFTED
SOUTHEASTWARD OVERNIGHT AND IS NOW LOCATED JUST A LITTLE FARTHER
SOUTH THAN PREVIOUSLY ESTIMATED. THE BEST ESTIMATE OF THE INITIAL
MOTION IS 125 DEGREES AT 3 KT.  LISA IS EXPECTED TO MOVE VERY
LITTLE DURING THE NEXT 48 HOURS AS IT REMAINS TRAPPED IN A
MID-LEVEL COL REGION BETWEEN A RIDGE TO THE EAST OVER AFRICA...A
RIDGE TO THE WEST OVER THE CENTRAL ATLANTIC...AND A SHARP TROUGH TO
THE NORTH BETWEEN THE AZORES AND CANARY ISLANDS.  AFTER 48
HOURS...THE TROUGH IS EXPECTED TO LIFT NORTHEASTWARD TOWARDS EUROPE
AND THE AFRICAN RIDGE WILL THEN BUILD WESTWARD...NUDGING LISA A
LITTLE FARTHER WEST OVER THE ATLANTIC.  THE TRACK GUIDANCE IS IN
AGREEMENT ON THIS SCENARIO... AND THE NHC FORECAST IS VERY CLOSE TO
THE MODEL CONSENSUS TVCN AND THE PREVIOUS FORECAST.

THE STRONGEST UPPER-LEVEL WINDS ARE LOCATED JUST NORTH OF THE
CYCLONE.  SINCE THE STORM IS LOCATED WITHIN THE COL...THE SHEAR
DIRECTLY OVER THE CENTER IS RATHER LOW AT THIS TIME.  HOWEVER...
THERE IS A LOT OF MID-LEVEL DRY AIR AROUND LISA...AND THAT COULD BE
WHAT IS PREVENTING INTENSIFICATION.  SOME STRENGTHENING IS STILL
POSSIBLE DURING THE NEXT 48 HOURS WHILE THE SHEAR REMAINS
RELATIVELY LOW...BUT INCREASING SHEAR AFTER THAT TIME SHOULD CAUSE
WEAKENING.  THERE IS GREATER SPREAD IN THE INTENSITY GUIDANCE AFTER
48 HOURS.  THE OFFICIAL INTENSITY FORECAST...WHICH HAS AGAIN BEEN
LOWERED A BIT FROM THE PREVIOUS FORECAST...IS CLOSE TO THE MODEL
CONSENSUS DURING THAT TIME.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      22/1500Z 17.1N  30.5W    40 KT
 12HR VT     23/0000Z 17.1N  30.3W    40 KT
 24HR VT     23/1200Z 17.0N  30.3W    45 KT
 36HR VT     24/0000Z 17.0N  30.7W    45 KT
 48HR VT     24/1200Z 17.3N  31.3W    50 KT
 72HR VT     25/1200Z 18.5N  33.0W    50 KT
 96HR VT     26/1200Z 20.0N  35.0W    45 KT
120HR VT     27/1200Z 21.5N  38.5W    35 KT
 
$$
FORECASTER BERG