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Hurricane Florence Forecast Discussion Number 23
2018-09-05 04:52:38| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Tue Sep 04 2018 797 WTNT41 KNHC 050252 TCDAT1 Hurricane Florence Discussion Number 23 NWS National Hurricane Center Miami FL AL062018 1100 PM AST Tue Sep 04 2018 GOES-16 imagery shows that the eye of Florence has become better defined during the last several hours, with even some mesovortices in the eye present on the shortwave infrared channel. Satellite intensity estimates continue to rise, and the initial wind speed is set to 85 kt, just below the latest TAFB estimate of 90 kt. Florence remains on a west-northwestward course at 300/10 kt. This general course is expected to continue through 36 or 48 hours while the hurricane remains near the southwestern edge of the subtropical ridge. After that time, the forecast becomes more uncertain, depending on the presence of a narrow mid-level ridge over the north-central Atlantic Ocean. A look at the ensemble guidance shows a bifurcation developing by day 5, with the ECMWF favoring a more northward turn, and the UKMET ensembles showing a stronger ridge and a continuation of a west-northwest track. The new NHC forecast is adjusted westward at long range, in line with the corrected-consensus aids, but don't be surprised if this forecast undergoes some large changes in the next few cycles, given the split in the guidance. This intensity forecast is also difficult. Florence certainly has exceeded expectations during the last day or so, with the hurricane on the verge of rapidly intensifying during the last 24 hours despite a marginal environment. Some more strengthening is called for in the short term to reflect the current trend. However, the global models continue to insist that southwesterly shear will increase over the next couple of days which, in combination with considerable dry air aloft, should cause some weakening. Later tomorrow, a slow weakening trend should begin and continue through 48 hours, although not weakening as much as shown in the past advisory. This can't be considered a high-confidence prediction in light of what Florence has done so far. On Friday, an upper-level low could cut off to the south of the cyclone, which would lessen the shear near Florence, and the hurricane should be moving over steadily increasing SSTs. Restrengthening is forecast at long range, and it wouldn't be surprising if the new NHC prediction turns out to be too low. It is best to be conservative, however, since the track uncertainty is increasing by the end of the forecast. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 20.7N 43.9W 85 KT 100 MPH 12H 05/1200Z 21.5N 45.5W 90 KT 105 MPH 24H 06/0000Z 22.6N 47.6W 80 KT 90 MPH 36H 06/1200Z 23.7N 49.4W 70 KT 80 MPH 48H 07/0000Z 24.7N 50.9W 65 KT 75 MPH 72H 08/0000Z 26.0N 53.5W 65 KT 75 MPH 96H 09/0000Z 27.3N 55.8W 70 KT 80 MPH 120H 10/0000Z 29.0N 57.5W 80 KT 90 MPH $$ Forecaster Blake
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