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| #872667 (Received by flhurricane at: 10:35 PM 21.Aug.2016) TCDAT1 TROPICAL DEPRESSION FIONA DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 1100 PM AST SUN AUG 21 2016 Deep convection continues to sputter near the center of Fiona, with each successive burst a little smaller and less organized than the previous ones that sheared off in the strong westerly upper-level winds. Given that earlier ASCAT data only showed a few 35-kt winds and the decrease in convective organization since that time, the initial intensity is set to 30 kt, which is also in agreement with the latest TAFB Dvorak estimate. The intensity forecast remains tricky. Fiona has been slowly weakening due to about 30 kt of westerly wind shear and mid-level dry air, and the NHC forecast shows the cyclone becoming a remnant low in the next 24 to 36 hours. However, the shear is forecast to decrease to 10 kt or less by 48 hours and the mid-levels begin to moisten according to the SHIPS model forecast. Therefore, if Fiona can survive the next 24 to 36 hours, the environment will become more conducive for restrengthening or maintaining the system as a tropical cyclone. The global models still disagree on the fate of Fiona, with the ECMWF showing dissipation in 2-3 days while the GFS and UKMET keep Fiona as a weak low through 5 days. The NHC forecast maintains continuity and indicates dissipation in 5 days as a compromise between these possibilities. The initial motion estimate is 290/16, as Fiona continues to move quickly west-northwestward under the influence of a low- to mid- level ridge over the central Atlantic. Fiona, or its remnants, will move around the western side of the ridge during the next several days, which should result is a poleward turn and a decrease in forward speed. The new NHC forecast is largely an update of the previous one through dissipation. There continues to be a fair amount of cross-track spread late in the period, and the NHC track still favors the GFS solution and lies to the right of the multi- model consensus. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 23.8N 56.6W 30 KT 35 MPH 12H 22/1200Z 24.5N 58.6W 30 KT 35 MPH 24H 23/0000Z 25.3N 60.9W 30 KT 35 MPH 36H 23/1200Z 26.2N 62.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 24/0000Z 27.0N 64.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 25/0000Z 29.0N 67.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 26/0000Z 30.5N 68.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 27/0000Z...DISSIPATED $$ Forecaster Brennan |
