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Tropical Storm Leslie Forecast Discussion Number 20
2018-10-01 10:53:37| National Hurricane Center (Atlantic)
Issued at 500 AM AST Mon Oct 01 2018 435 WTNT43 KNHC 010853 TCDAT3 Tropical Storm Leslie Discussion Number 20 NWS National Hurricane Center Miami FL AL132018 500 AM AST Mon Oct 01 2018 Leslie has become a little better organized overnight, with an increase in convective banding over the northern and northwestern portions of the circulation. ASCAT data around 0000 UTC revealed 40-45 kt winds over the northeastern quadrant of the cyclone and with the increase in organization since that time, the initial intensity has been raised to 50 kt. This is a little above the consensus Dvorak intensity estimates of T3.0 (45 kt) from TAFB and SAB. The shear that was affecting Leslie appears to have abated somewhat and with the system forecast to move southwestward toward slightly warmer waters, gradual strengthening is expected during the next couple of days. Later in the period, Leslie is forecast to move north-northeastward back over its previous track where cooler upwelled waters are likely to produce some weakening. The updated NHC intensity forecast shows a slightly higher peak intensity in 48 to 72 hours, but remains between the dynamical model guidance and the higher statistical models. Leslie continues to plod along with an initial motion estimate of 240/4 kt. The cyclone should move slowly southwestward to southward during the next couple of days as it remains within an area of weak steering currents. After that time, a shortwave trough to the northwest of Leslie is expected to allow the tropical cyclone to lift slowly north-northeastward by days 4 and 5. Although the dynamical model guidance is in agreement on this overall scenario, there is increasing cross-track (east-west) spread after 72 hours. The latest run of the ECMWF has shifted westward and brackets the western edge of the guidance envelope. The new NHC track forecast has been shifted in that direction, but it is not as far left as the various consensus aids out of respect of the previous track forecast. Regardless of the details of the forecast track, Leslie is still expected to meander over the central Atlantic through the remainder of this week. Large swells generated by Leslie when it was a strong extratropical low will continue to affect portions of the southeastern coast of the United States, Bermuda, the Bahamas, and most of the Greater and Lesser Antilles for another day or two. These swells could cause life-threatening surf and rip currents. Although the swells will diminish some by mid-week, they will likely remain hazardous for the same locations through the forecast period due to Leslie's slow motion. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 33.4N 53.9W 50 KT 60 MPH 12H 01/1800Z 33.1N 54.5W 55 KT 65 MPH 24H 02/0600Z 32.2N 55.3W 60 KT 70 MPH 36H 02/1800Z 31.2N 55.8W 65 KT 75 MPH 48H 03/0600Z 30.6N 56.0W 70 KT 80 MPH 72H 04/0600Z 31.7N 55.2W 70 KT 80 MPH 96H 05/0600Z 35.0N 54.3W 65 KT 75 MPH 120H 06/0600Z 37.4N 52.0W 60 KT 70 MPH $$ Forecaster Brown
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