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Hurricane Beryl Forecast Discussion Number 5
2018-07-06 16:36:35| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Fri Jul 06 2018 000 WTNT42 KNHC 061436 TCDAT2 Hurricane Beryl Discussion Number 5 NWS National Hurricane Center Miami FL AL022018 1100 AM AST Fri Jul 06 2018 Beryl is a compact hurricane that had a pinhole eye for a few hours before more recently becoming cloud filled again. Satellite intensity estimates from TAFB and SAB were T4.0/65 kt at 12Z, but the Dvorak technique is constrained by width requirements of the convective cloud tops. That may not be applicable in this case given Beryl's extremely small size. By disregarding the width constraints, TAFB was able to provide a data-T number of T4.5/77 kt. As a compromise, the initial intensity is raised to 70 kt. Beryl has not gained much latitude and is still moving quickly westward with a 12-hour motion estimate of 275/13 kt. Mid-level ridging over the subtropical Atlantic is expected to steer Beryl on a westward to west-northwestward course through the forecast period. An acceleration is forecast to begin in 36-48 hours once Beryl becomes situated to the south of the core of the mid-level anticyclone. Some of the track models have already shown a northward bias since the cyclone formed yesterday, and the updated NHC track forecast is therefore south of the typically better- performing models. This new forecast is not too different from the previous NHC track and is also just south of the HCCA model and the various model consensus aids. Despite the SHIPS model diagnostics showing increasing shear in a few days, global model fields show a well-defined upper-level anticyclone following the system at least for the next 3 days. Although Beryl's expected acceleration may contribute to some increased shear, the SHIPS model is also probably calculating deep-layer shear over too large an area to accurately capture the shear isolated to the cyclone's scale. Given that, the NHC intensity forecast is at or above nearly all of the guidance through 48 hours, which is also higher than what we've been depicting in previous forecasts. Needless to say, it's becoming more likely that Beryl will maintain hurricane strength when it reaches the Lesser Antilles between 48 and 72 hours. The cyclone is also now likely to persist beyond the 72-hour forecast point, and a 96-hour point has therefore been added to the official forecast, showing Beryl near or over Hispaniola by day 4. By that point, either increased shear or the terrain of Hispaniola would likely lead to dissipation. But we shall see. Key Messages: 1. Beryl is now expected to be a hurricane when it moves through the Lesser Antilles Sunday night or Monday, and the chance of some islands receiving direct impacts from wind and rainfall are increasing. However, Beryl is a very small hurricane, and it is too early to determine exactly where those impacts will occur. Hurricane watches could be needed for portions of the Lesser Antilles as soon as tonight. 2. Due to its very small size, there is greater-than-usual uncertainty in the analysis of Beryl's current intensity, and confidence in the official intensity forecast is also lower than normal. Rapid changes in intensity, both up and down, that are difficult to predict are possible during the next couple of days. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 10.7N 46.5W 70 KT 80 MPH 12H 07/0000Z 11.3N 47.9W 75 KT 85 MPH 24H 07/1200Z 12.2N 50.1W 80 KT 90 MPH 36H 08/0000Z 13.3N 53.0W 85 KT 100 MPH 48H 08/1200Z 14.2N 56.6W 85 KT 100 MPH 72H 09/1200Z 16.2N 64.6W 60 KT 70 MPH 96H 10/1200Z 18.5N 72.0W 40 KT 45 MPH...INLAND OVER HISPANIOLA 120H 11/1200Z...DISSIPATED $$ Forecaster Berg
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