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#875480 (Received by flhurricane at: 4:34 AM 21.Sep.2016) TCDAT3 TROPICAL STORM LISA DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132016 500 AM AST WED SEP 21 2016 Lisa`s cloud pattern has gradually become better organized into a comma-like shape, although the system still appears to be somewhat elongated from southwest to northeast. Upper-level outflow remains weak over the southeastern quadrant of the circulation. Dvorak classifications from both TAFB and SAB yield an intensity estimate of 45 kt, and that value is used for the advisory. The storm has less than 24 hours before west-southwesterly shear associated with an upper-level trough near 40W-50W longitude becomes prohibitively large for strengthening. Therefore, some slight additional intensification could occur today, but beyond 24 hours Lisa is forecast to steadily weaken. By days 4-5, although the shear is predicted to weaken when Lisa moves under the trough axis, the cyclone should have been disrupted too much by the earlier hostile environment to make a recovery. The official forecast is close to the LGEM guidance through 48 hours and a little below that model thereafter. The center is not easy to locate and the initial motion is a rather uncertain 315/8 kt, which is partially based on continuity from earlier estimates. A weak mid-tropospheric ridge to the north and northeast of Lisa should maintain a generally northwestward motion through 72 hours or so. Later in the forecast period, an approaching trough in the westerlies, which is also expected to accelerate Karl to the northeast, should cause Lisa to turn northward over the eastern Atlantic. The official track forecast is similar to the previous one and is close to a consensus of the ECMWF, GFS, and UKMET global models. FORECAST POSITIONS AND MAX WINDS INIT 21/0900Z 17.5N 32.2W 45 KT 50 MPH 12H 21/1800Z 18.2N 33.2W 50 KT 60 MPH 24H 22/0600Z 19.1N 34.5W 50 KT 60 MPH 36H 22/1800Z 20.1N 35.9W 45 KT 50 MPH 48H 23/0600Z 21.3N 37.4W 40 KT 45 MPH 72H 24/0600Z 24.1N 40.4W 30 KT 35 MPH 96H 25/0600Z 27.5N 43.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 26/0600Z 32.5N 43.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Pasch |