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| #943671 (Received by flhurricane at: 10:41 AM 09.Oct.2018) TCDAT3 Tropical Storm Leslie Discussion Number 53 NWS National Hurricane Center Miami FL AL132018 1100 AM AST Tue Oct 09 2018 Recent Dvorak fixes and ASCAT data indicate that Leslie`s maximum winds remain around 55 kt. Although the winds have not yet increased, the surface center of the tropical storm has become more embedded within its cold cloud tops and several recent microwave overpasses indicate that the cyclone is beginning to establish an inner-core. Strengthening is therefore still expected, and Leslie is forecast to become a hurricane by tomorrow. The tropical storm is currently moving south-southeastward at around 11 kt, and the models are in good agreement that a south-southeastward to southward motion will continue for the next 24 h or so. Beginning around 36 h, both the track and intensity forecasts become very uncertain. In general, most of the global models and their ensembles indicate that Leslie will begin to accelerate toward the east-northeast or northeast by Thursday as a mid-latitude trough approaches from the northwest, however the timing and extent of the interaction is still highly variable from model to model. Based on the GFS and ECMWF ensembles, a range of possibilities exists, from Leslie essentially merging with this trough and becoming extratropical over the far northeast Atlantic, to Leslie interacting with the trough very little and continuing to meander over the central Atlantic. There has been a significant change in the consensus aids to show a slower track for Leslie based on recent shifts in the deterministic models, but the NHC track forecast has not been changed nearly as much, out of respect for continuity and the high uncertainty in the forecast. The low confidence in the track forecast beyond 36 h affects the intensity forecast as well, since it is unclear what environment the storm will be located within. The intensity forecast is therefore held near the intensity consensus, and still calls for steady strengthening during the next several days, followed by weakening by the end of the forecast period. If Leslie moves as far east as shown in the NHC track forecast, it would likely become a post- tropical low by day 5, as shown explicitly in the forecast. However, until confidence in the track increases, I can`t rule out that Leslie could remain a tropical cyclone almost indefinitely if it continues meandering over the northern Atlantic. FORECAST POSITIONS AND MAX WINDS INIT 09/1500Z 31.3N 43.5W 55 KT 65 MPH 12H 10/0000Z 29.9N 42.9W 55 KT 65 MPH 24H 10/1200Z 28.5N 42.6W 60 KT 70 MPH 36H 11/0000Z 28.1N 41.7W 65 KT 75 MPH 48H 11/1200Z 28.9N 39.5W 70 KT 80 MPH 72H 12/1200Z 32.0N 31.5W 75 KT 85 MPH 96H 13/1200Z 33.5N 22.0W 65 KT 75 MPH 120H 14/1200Z 33.5N 18.0W 50 KT 60 MPH...POST-TROPICAL $$ Forecaster Zelinsky |
