ZCZC MIATCDAT2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM LISA DISCUSSION NUMBER 6 NATIONAL WEATHER SERVICE MIAMI FL 11 PM EDT TUE OCT 06 1998 THE STORM CONTINUES TO BE SHEARED BY SOUTHWESTERLY FLOW ASSOCIATED WITH AN UPPER-LEVEL LOW LOCATED NEAR 21N 53W. SINCE LISA IS MOVING NORTHEASTWARD...THE SHEAR IS NOT AS STRONG AS IT WOULD BE FOR A WESTWARD-MOVING TROPICAL CYCLONE...BUT STILL STRONG ENOUGH TO PREVENT SIGNIFICANT INTENSIFICATION. THE UPPER LOW APPEARS TO BE DRIFTING SOUTHEASTWARD. IF THE UPPER LOW CONTINUES MOVING SOUTHEAST AND LISA CONTINUES MOVING NORTHEAST...THE HIGH-LEVEL FLOW OVER THE STORM MAY BECOME MORE FAVORABLE FOR STRENGTHENING IN A DAY OR SO. ON THE OTHER HAND...THE LARGE MID- TO UPPER-LEVEL TROUGH FARTHER TO THE NORTH WILL PROBABLY CONTRIBUTE TO INCREASED SHEAR LATER IN THE PERIOD. THE SHIPS MODEL...WHICH USES THE AVN MODEL FORECAST WINDS...SHOWS SOME RELAXATION OF THE SHEAR DURING THE NEXT 24 HOURS AND AN INCREASE THEREAFTER. GIVEN THE UNCERTAINTIES...INTENSITY IS HELD CONSTANT IN THE OFFICIAL FORECAST. BY 72 HOURS LISA IS EXPECTED TO BE COMBINING WITH A FRONTAL CYCLONE OVER THE CENTRAL ATLANTIC...AND SHOULD BE LOSING ITS TROPICAL CHARACTERISTICS. AS USUAL FOR THIS TYPE OF SYSTEM...WITHOUT VISIBLE SATELLITE PICTURES...IT IS QUITE DIFFICULT TO LOCATE THE CENTER. HOWEVER THE TPC 2-INFRARED CHANNEL COMBINATION IMAGERY INDICATES THAT THE CENTER IS VERY LIKELY NEAR THE SOUTHWEST EDGE OF THE MAIN CONVECTIVE OVERCAST. INITIAL MOTION ESTIMATE IS JUST SLIGHTLY SLOWER...040/09. A LARGE 500 MB TROUGH IS FORECAST BY THE NCEP GLOBAL MODEL TO PRODUCE A STRONG CUT-OFF LOW OVER THE CENTRAL ATLANTIC IN A COUPLE OF DAYS. LISA IS EXPECTED TO BE STEERED NORTHEASTWARD TO NORTHWARD AROUND THE EASTERN SIDE OF THIS LOW. THE OFFICIAL TRACK FORECAST IS SIMILAR TO THAT FROM THE PREVIOUS ADVISORY...AND TO THE 18Z GFDL MODEL RUN ALBEIT NOT AS FAST NEAR THE END OF THE PERIOD. PASCH FORECAST POSITIONS AND MAX WINDS INITIAL 07/0300Z 19.6N 48.0W 45 KTS 12HR VT 07/1200Z 20.8N 46.8W 45 KTS 24HR VT 08/0000Z 22.5N 45.0W 45 KTS 36HR VT 08/1200Z 25.0N 43.0W 45 KTS 48HR VT 09/0000Z 28.0N 40.5W 45 KTS 72HR VT 10/0000Z 38.0N 40.0W 45 KTS...EXTRATROPICAL NNNN