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| #990378 (Received by flhurricane at: 10:12 PM 23.Nov.2019) TCDAT5 Tropical Storm Sebastien Discussion Number 19 NWS National Hurricane Center Miami FL AL202019 1100 PM AST Sat Nov 23 2019 Over the large scale, Sebastien appears to be undergoing extratropical transition, with a large cirrus shield on the northern side of the storm and unimpressive convection overall. Near the center, however, the storm still has a small inner core, with what appears to be a faint eye feature forming during the past few hours in conventional satellite imagery. This feature also shows up in recent microwave data, suggesting that Sebastien still has more of its tropical character than a cursory look would indicate. Thus, Sebastien is held as a tropical cyclone and, since Dvorak and SATCON estimates remain at 55 kt, the initial wind speed is held at that value. Unfortunately all 3 scatterometer satellites missed the cyclone this evening. Sebastien is quickly moving up on my list of most annoying storms during the 2019 season, and hopefully this isn`t another night of it making my forecast look silly. I think (hope?) the intensity outlook is getting easier since the storm will be moving over sub-20C waters by tomorrow morning. There are no signs of significant upper-level cooling at that time, so Sebastien will probably be struggling to produce any organized deep convection. Since baroclinic forcing also appears to be on the wane, a slow weakening is anticipated, and a more complete extratropical transition is forecast by this time tomorrow. This is also indicated by cyclone phase space diagrams derived from the GFS and ECMWF models. While I might have a little more confidence in this prediction than a couple of days ago, I also wouldn`t be surprised if Sebastien had another trick up its sleeve. The storm is accelerating northeastward, now estimated at 045/27 kt. The evening model guidance continues the trend noted by my predecessor of a faster motion, so the new NHC prediction is shifted in that direction, and somewhat to the north. Sebastien or its extratropical remnants are expected to bring gusty winds and rain to the Azores beginning on Sunday. Please see products issued by the Portuguese Institute for the Sea and the Atmosphere (IPMA) for more information. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 34.4N 43.1W 55 KT 65 MPH 12H 24/1200Z 37.0N 38.7W 55 KT 65 MPH 24H 25/0000Z 40.1N 31.1W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 25/1200Z 43.9N 22.3W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 26/0000Z 48.0N 14.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 27/0000Z...DISSIPATED $$ Forecaster Blake |
