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Tropical Storm FIONA Forecast Discussion Number 17
2016-08-21 04:49:45| National Hurricane Center (Atlantic)
Issued at 1100 PM AST SAT AUG 20 2016 000 WTNT41 KNHC 210249 TCDAT1 TROPICAL STORM FIONA DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 1100 PM AST SAT AUG 20 2016 Somewhat surprisingly, two recent ASCAT passes showed that Fiona is producing 45-kt winds in its northeastern quadrant. This intensity is also supported by the latest ADT estimate. Despite the increase in maximum winds, the next 36 hours will be critical for Fiona's survival as a tropical cyclone. During this period, westerly shear of 30 kt will be at its strongest, and mid-level relative humidities will be at their lowest. Therefore, gradual weakening is anticipated, and it's entirely possible that Fiona could soon struggle to maintain organized deep convection. For now, the NHC official forecast shows Fiona becoming a remnant low by 72 hours. However, there is a lot of uncertainty in this forecast. If Fiona can survive the next 36 hours, it might persist as a weak tropical cyclone through the end of the forecast period since environmental conditions do become a little more favorable in a couple of days. It should be noted that most of the global models hang onto a weak low for at least the next 5 days, with the exception of the ECMWF which shows the low opening up into a trough by 48 hours. For now, the NHC forecast continues to show dissipation by day 5 as a compromise. Fiona's motion has been wavering between west-northwest and northwest, and the latest estimate is 305/13 kt. Low-level ridging should keep Fiona on this general trajectory for the next 72 hours or so, followed by a northwestward turn with a decrease in speed by day 4 when the cyclone approaches a stalled frontal boundary off the east coast of the United States. The NHC official forecast has been nudged south and west to be closer to the TVCN multi-model consensus, especially toward the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 21.7N 50.1W 45 KT 50 MPH 12H 21/1200Z 22.4N 52.0W 45 KT 50 MPH 24H 22/0000Z 23.3N 54.6W 40 KT 45 MPH 36H 22/1200Z 24.2N 57.3W 40 KT 45 MPH 48H 23/0000Z 24.9N 59.5W 35 KT 40 MPH 72H 24/0000Z 26.6N 63.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 25/0000Z 29.0N 66.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 26/0000Z...DISSIPATED $$ Forecaster Berg
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