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| #1024902 (Received by flhurricane at: 10:06 PM 11.Nov.2020) TCDAT5 Tropical Storm Theta Discussion Number 9 NWS National Hurricane Center Miami FL AL302020 300 AM GMT Thu Nov 12 2020 The cloud appearance of Theta briefly became a bit more symmetric earlier tonight, though the colder cloud tops that attempted to wrap around the low-level center have recently decayed, possibly due to entrainment of dry mid-latitude air. A 2243 UTC ASCAT-B pass and a subsequent ASCAT-C pass both found the max winds with Theta a little stronger than previously estimated with maximum values exceeding 50 kt. These data support an initial intensity of 55 kt, and this could even be a little conservative. Over the last 6 h Theta appears to have made a slight jog left of the previous forecast track, perhaps related to the convection wrapping around the center, but the longer term motion is still east-northeast at about 10 kt. Over the next day, Theta is expected to continue to move east-northeastward as it rounds the north side of a mid-level ridge centered over the Cape Verde islands. Between 48 h to 72 h Theta`s track is forecast to bend east and then east-southeast as the mid-level ridge to the south weakens a bit, and mid to upper-level northerly flow from a weak mid-level ridge attempts to build in to the west. The latest track guidance shows a fair amount of spread in how quickly Theta makes this bend to the east-southeast, and this is a large source of uncertainty in the forecast. The NHC track forecast splits the difference between the faster ECMWF and slower HMON/HWRF guidance, and is not far from the TVCN consensus. The intensity forecast of Theta has been adjusted upward for the first 48 h due to the higher initial intensity. GFS-SHIPS diagnostics indicate the vertical wind shear will gradually decrease while Theta moves through an unstable temperature profile conducive for moderate to deep convection. Thereafter, the aforementioned upper-level northerly flow will lead to an increase in the vertical wind shear and import very stable mid-latitude air over Thetas circulation. Most of the reliable global model guidance shows Theta succumbing to these negative effects and becoming a remnant low by 96 h. The official intensity forecast shows the same, and is on the high side of the guidance but not far from any of the models since the spread is quite low. FORECAST POSITIONS AND MAX WINDS INIT 12/0300Z 31.1N 31.4W 55 KT 65 MPH 12H 12/1200Z 31.5N 29.8W 55 KT 65 MPH 24H 13/0000Z 32.0N 27.8W 55 KT 65 MPH 36H 13/1200Z 32.1N 25.4W 55 KT 65 MPH 48H 14/0000Z 31.8N 23.4W 50 KT 60 MPH 60H 14/1200Z 31.4N 21.9W 45 KT 50 MPH 72H 15/0000Z 31.2N 20.5W 40 KT 45 MPH 96H 16/0000Z 31.2N 19.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 17/0000Z 35.6N 18.9W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Papin/Zelinsky |
