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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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