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Subtropical Depression Leslie Forecast Discussion Number 7
2018-09-25 04:33:13| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Mon Sep 24 2018 574 WTNT43 KNHC 250233 TCDAT3 Subtropical Depression Leslie Discussion Number 7 NWS National Hurricane Center Miami FL AL132018 1100 PM AST Mon Sep 24 2018 Leslie's appearance in satellite imagery hasn't changed much this evening. Deep convection is mainly occuring in bands well displaced to the southeast of the cyclone's center, and recent ASCAT data indicated that the maximum winds have decreased to near 30 kt, with the highest wind occuring in those bands. All indications are that Leslie will undergo a complicated transition over the next several days. Little change is expected with Leslie until it becomes post-tropical in about 24 hours. After that time, all of the global models suggest that Leslie will quickly strengthen as a result of substantial baroclinic forcing, likely reaching a peak intensity sometime between 48 and 72 h. At the same time, the cyclone will likely undergo a classic transition from frontal low to warm seclusion while the wind field rapidly expands, with 34-kt (gale-force) winds reaching several hundred miles from the cyclone's center. By 96 h, the models indicate that Leslie will once again become cut-off from the mid-latitude flow, and could begin to re-acquire subtropical or tropical characteristics. While each of the global models handles the exact details of this complex evolution a little differently, confidence is increasing that Leslie will become a powerful extratropical cyclone over the central Atlantic over the next few of days. The NHC intensity forecast has been increased between 36 and 96 h, and is near a average of the global and regional dynamical model tracker output. The depression is currently moving slowly eastward with an initial motion of 090/3 kt. The guidance is in good agreement that Leslie will accelerate eastward as it becomes more embedded within an approaching frontal zone. A northward turn is expected by mid-week, followed by a bend back toward the west by the end of the week as Leslie strengthens, occludes, and eventually cuts off from the mid-latitude flow to the north. The NHC track forecast has not been significantly changed, and is near the GFEX and HCCA consensus aids at most forecast hours. However, it should be noted that spread in the guidance is high, especially by the end of the forecast period, so confidence in the track forecast at that time is low. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 33.1N 47.1W 30 KT 35 MPH 12H 25/1200Z 32.9N 45.6W 30 KT 35 MPH 24H 26/0000Z 33.1N 43.2W 40 KT 45 MPH...POST-TROPICAL 36H 26/1200Z 34.5N 41.1W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 27/0000Z 36.2N 40.9W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 28/0000Z 36.9N 43.8W 60 KT 70 MPH...POST-TROP/EXTRATROP 96H 29/0000Z 36.5N 47.3W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 30/0000Z 36.5N 49.0W 50 KT 60 MPH...SUBTROPICAL STORM $$ Forecaster Zelinsky
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