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Tropical Storm FIONA Forecast Discussion Number 9
2016-08-19 04:43:23| National Hurricane Center (Atlantic)
Issued at 1100 PM AST THU AUG 18 2016 000 WTNT41 KNHC 190243 TCDAT1 TROPICAL STORM FIONA DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 1100 PM AST THU AUG 18 2016 A sizable burst of deep convection has been ongoing since late this afternoon, and recent microwave imagery suggests that the low-level center may be a little closer to the thunderstorm activity than it was for most of the day. Still, Dvorak estimates are unchanged at T3.0/45 kt from TAFB and T2.5/35 kt from SAB, and the initial intensity remains 40 kt. Fiona's window for any strengthening is narrowing. SHIPS guidance is currently analyzing 10-15 kt of south-southwesterly shear, while the UW-CIMSS analysis has the shear as high as 20-25 kt. Despite the discrepancy, these values suggest the shear is already increasing, and it is expected to increase further and become more westerly during the next three days. Therefore, if the current burst of convection continues, Fiona has a chance to strengthen slightly during the next 12 hours and then gradually weaken through days 3 and 4. The forecast trends in the intensity models suggest that Fiona could weaken to a tropical depression, which is now shown in the official forecast. Environmental conditions appear to be a little less hostile by the end of the forecast period, and the NHC forecast allows for the possibility that Fiona could restrengthen after the shear lightens up. The GFDL continues to be an outlier by intensifying Fiona more than the other models, and the official intensity forecast is therefore near or just below the intensity consensus for most of the forecast period. Microwave fixes indicate that Fiona has been moving more slowly toward the northwest, or 305/7 kt. The cyclone is moving toward a break in the subtropical ridge located between 40W-55W, and an amplifying deep-layer trough over the north Atlantic is expected to maintain this break for the next several days. By continuing on a northwestward heading, Fiona is expected to reach the axis of the subtropical ridge and turn northward by day 5. The GFDL is still well to the northeast of the rest of the track guidance since it carries a much stronger system, but the other models are otherwise in very good agreement. Therefore, no significant changes were made to the NHC track forecast, which remains close to the TVCN multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 17.1N 41.8W 40 KT 45 MPH 12H 19/1200Z 17.8N 43.1W 45 KT 50 MPH 24H 20/0000Z 18.7N 44.9W 40 KT 45 MPH 36H 20/1200Z 19.8N 46.9W 35 KT 40 MPH 48H 21/0000Z 20.9N 48.9W 35 KT 40 MPH 72H 22/0000Z 23.0N 53.2W 30 KT 35 MPH 96H 23/0000Z 25.0N 56.5W 30 KT 35 MPH 120H 24/0000Z 27.5N 57.0W 35 KT 40 MPH $$ Forecaster Berg
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