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Tropical Storm Leslie Forecast Discussion Number 14
2018-09-29 22:33:53| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sat Sep 29 2018 106 WTNT43 KNHC 292033 TCDAT3 Tropical Storm Leslie Discussion Number 14 NWS National Hurricane Center Miami FL AL132018 500 PM AST Sat Sep 29 2018 Leslie has continued to take on more tropical characteristics over the past few hours. Anti-cyclonic outflow is now present to the northeast and southeast of Leslie and its primary convective band. Late-arriving AMSU data from 1316 UTC also indicated that Leslie has developed a deep-layer warm core structure. Based on these factors, Leslie has been designated as a tropical storm. The initial intensity is set at 45 kt, based on a blend of recent satellite intensity estimates from TAFB and the UW-CIMSS SATCON. Leslie continues to move slowly southwestward with an initial motion of 225/5 kt. The guidance is in very good agreement that this general motion will continue for another 24 h or so, before the cyclone becomes nearly stationary by early next week. An approaching mid-latitude trough is still expected to eventually cause Leslie to turn toward the north or northeast, perhaps over its own track, in 4 or 5 days. Only minor adjustments were made to the NHC track forecast, which remains close to the various track consensus aids. The NHC intensity forecast has not been changed in any significant way and remains near the intensity consensus, but slightly favors the regional hurricane models. Leslie is currently located over fairly cool SSTs, and its slow motion could cause further ocean cooling. This could particularly be an issue in a few days when the tropical storm is expected to become nearly stationary. The ocean-coupled regional models (HWRF, HMON, COAMPS-TC) continue to indicate that Leslie will struggle to intensify much over the next few days, despite a fairly favorable upper-level environment. On the other hand, some of the uncoupled global models and the SHIPS and LGEM models suggest that more intensification will occur and that Leslie could become a hurricane in a few days. Highlighting the potential importance of SSTs in this case, the SHIPS and LGEM models began using daily SST fields at 18Z, which show nearly 2 deg C cooler SSTs along the track of Leslie, and those models now show much less intensification than they did before. Large swells generated by Leslie when it was a strong extratropical low will affect Bermuda, the east coast of the United States, and most of the Greater and Lesser Antilles through the weekend. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 34.1N 51.3W 45 KT 50 MPH 12H 30/0600Z 33.6N 52.0W 45 KT 50 MPH 24H 30/1800Z 33.1N 53.0W 50 KT 60 MPH 36H 01/0600Z 32.8N 53.5W 50 KT 60 MPH 48H 01/1800Z 32.5N 53.9W 55 KT 65 MPH 72H 02/1800Z 31.5N 54.7W 55 KT 65 MPH 96H 03/1800Z 31.5N 54.5W 60 KT 70 MPH 120H 04/1800Z 34.0N 54.0W 65 KT 75 MPH $$ Forecaster Zelinsky
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