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Post-Tropical Cyclone Leslie Forecast Discussion Number 9
2018-09-25 16:40:18| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Tue Sep 25 2018 676 WTNT43 KNHC 251439 TCDAT3 Post-Tropical Cyclone Leslie Discussion Number 9 NWS National Hurricane Center Miami FL AL132018 1100 AM AST Tue Sep 25 2018 Leslie has become a post-tropical cyclone. Conventional and microwave satellite imagery show that Leslie's surface circulation has become elongated along an intruding baroclinic zone indicated by a recent 1158 UTC ASCAT-A pass. Any deep convection appears to be developing due to dynamic forcing. A rather large stratocumulus cloud shield and associated cooler, stable air is quickly advecting into the area as well. The initial intensity is maintained at 30 kt for this last advisory. Leslie is forecast to strengthen during the next couple of days due to baroclinic processes. The official forecast, based on the GFS and European global models, and the SHIPS statistical intensity guidance, shows an increase of the sustained winds to hurricane force in 2 days, around the same period that the shear drops below 10 kt. The non-tropical low is then forecast to move south of the strong upper-level westerlies and detach from the frontal boundary. According to the global models and the Florida State Cyclone Phase forecast, Leslie should make a transition from a frontal system to an asymmetric shallow warm-core seclusion. Beyond day 3, guidance suggests that Leslie will acquire subtropical characteristics and a more symmetric, deepening warm-core low while meandering in weaker steering currents. The intensity forecast follows this scenario and is based on the aforementioned global and statistical models. Leslie is now moving eastward at a slightly faster forward motion, about 10 kt. A turn to the north is expected in 36 hours followed by a slower westward motion as Leslie slips south of the mid-latitude westerlies. Through the remaining portion of the forecast, Leslie should move at a slower speed generally westward as a ridge builds to the north. NHC forecast is nudged toward the TVCN consensus through 48 hours, then follows more closely to the GFEX (GFS/ECMWF) consensus model. This is the last advisory issued by the National Hurricane Center on Leslie. Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and available on the Web at https://ocean.weather.gov/shtml/NFDHSFAT1.shtml. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 31.6N 44.4W 30 KT 35 MPH...POST-TROPICAL 12H 26/0000Z 32.1N 42.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 24H 26/1200Z 33.6N 40.1W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 27/0000Z 35.6N 39.9W 60 KT 70 MPH...POST-TROP/EXTRATROP 48H 27/1200Z 36.1N 41.7W 65 KT 75 MPH...POST-TROP/EXTRATROP 72H 28/1200Z 35.5N 45.3W 60 KT 70 MPH...SUBTROPICAL STORM 96H 29/1200Z 34.6N 48.1W 55 KT 65 MPH...SUBTROPICAL STORM 120H 30/1200Z 34.4N 49.6W 50 KT 60 MPH...SUBTROPICAL STORM $$ Forecaster Roberts
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