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Tropical Storm Florence Forecast Discussion Number 33
2018-09-07 16:47:27| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Fri Sep 07 2018 241 WTNT41 KNHC 071447 TCDAT1 Tropical Storm Florence Discussion Number 33 NWS National Hurricane Center Miami FL AL062018 1100 AM AST Fri Sep 07 2018 Moderate to strong southwesterly shear continues to affect Florence, but visible and microwave satellite images indicate that the cyclone is maintaining a vigorous, but tilted, circulation. A mid-level eye feature is noted in both types of satellite imagery, but the low-level center still appears displaced to the southwest. Subjective and objective satellite intensity estimates have stopped falling--and some have even begun to increase a bit again--so the initial intensity is being held at 55 kt. The shear over Florence has likely reached its maximum and is expected to decrease below 20 kt in 6-12 hours and then decrease to 10 kt or less in 36 hours. All the while, sea surface temperatures will be gradually increasing to between 28-29C, and perhaps more importantly, oceanic heat content values will double in 3-4 days. It may take the cyclone some time to gather itself once the shear abates, but once it becomes vertically stacked again, the intensity is likely to increase significantly. The guidance is in agreement on this scenario, and Florence is likely to re-attain hurricane status in about 48 hours and then potentially major hurricane strength by days 4-5. The new official forecast is fairly similar to the previous one, generally close to the ICON intensity consensus and slightly below the HCCA model on days 4 and 5. Florence is moving westward, or 270/7 kt, to the south of the eastern periphery of a subtropical ridge extending east of the Mid-Atlantic United States. The global model guidance is actually in fairly good agreement on the general evolution of the steering pattern around Florence through day 5. While it remains a tilted cyclone, Florence is expected to continue moving westward for the next 48 hours. After that time, a break in the ridge should allow Florence to turn west-northwestward over the southwestern Atlantic. A new mid-level ridge is expected to develop over the western Atlantic on days 4-5, but the position of that high will play a big role regarding how much Florence may turn by the end of the forecast period. Only a slight southward nudge of forecast track was required on this cycle, keeping the NHC prediction between the GFS and ECMWF solutions. Key Messages: 1. Regardless of Florence's eventual track, large swells will begin to affect Bermuda later today and portions of the U.S. East Coast this weekend, resulting in life-threatening surf and rip currents. 2. The risk of other direct impacts associated with Florence along the U.S. East Coast next week has increased. However, there is still very large uncertainty in model forecasts of Florence's track beyond day 5, making it too soon to determine the exact location, magnitude, and timing of these impacts. Interests near and along the U.S. East Coast should monitor the progress of Florence through the weekend and ensure they have their hurricane plans in place. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 25.0N 51.8W 55 KT 65 MPH 12H 08/0000Z 24.9N 52.8W 55 KT 65 MPH 24H 08/1200Z 24.9N 54.0W 55 KT 65 MPH 36H 09/0000Z 24.9N 55.1W 60 KT 70 MPH 48H 09/1200Z 25.1N 56.2W 65 KT 75 MPH 72H 10/1200Z 25.9N 59.8W 90 KT 105 MPH 96H 11/1200Z 27.5N 65.5W 110 KT 125 MPH 120H 12/1200Z 30.0N 72.0W 115 KT 130 MPH $$ Forecaster Berg
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