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Tropical Storm Beryl Forecast Discussion Number 3
2018-07-06 04:31:58| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Thu Jul 05 2018 000 WTNT42 KNHC 060231 TCDAT2 Tropical Storm Beryl Discussion Number 3 NWS National Hurricane Center Miami FL AL022018 1100 PM AST Thu Jul 05 2018 Tiny Beryl has maintained a small ball of convection near the center except for a brief period around 2300 UTC when a tight curved band was exposed, revealing 10- to 11-tenths banding. Passive microwave satellite data during the past 6 hours have also indicated 5-nmi-diameter eye exists underneath the CDO feature. Given the small size of the cyclone, which can quickly adjust to convective changes, and a Dvorak satellite estimate of T3.5/55 kt from SAB, the advisory intensity has been increased to 55 kt. The initial motion estimate is 275/12 kt. Most of the latest model guidance has made a pronounced southward shift, which is significant since all of the models have displayed a distinct right-of-track, poleward bias over the past 48 hours. The ECMWF has had the greatest poleward bias, and is now the northernmost solution in the model suite. The GFS, HWRF, and UKMET are now clustered along the southern edge of the guidance envelope, with the consensus models somewhere in between those latter models and the ECMWF. Given the very small size of Beryl, I am having difficulty envisioning the cyclone moving into the strong subtropical ridge situated to its north and gaining as much latitude as the ECMWF has been and is still indicating. As a result, the new NHC forecast track has been shifted south of the previous advisory track, but not as far south as the GFS-HRWF-UKMET consensus, and lies a tad south of the HCCA and FSSE solutions. Water vapor and model moisture analyses indicate that Beryl has been able to maintain a buffer between it and the very dry, stable air just to its north, due in large part to the deep, southerly moisture fetch coming up from the equatorial region. This pattern is forecast by most of the global models to continue for at least the next 48 hours. That favorable environment, coupled with forecast low vertical wind shear conditions of near 5 kt for the next 24 hours, should allow Beryl to achieve hurricane status by late Friday. By 72 hours when Beryl will be approaching the Lesser Antilles, the shear is forecast to increase from the west and northwest at 20-25 kt, which is expected to induce rapid weakening. All of the global models continue to show the cyclone opening up into a tropical wave shortly after 72 hours, which is what the current forecast continues to depict in order to maintain continuity with the previous advisory track. However, only a slight delay in the onset of the strong shear conditions could result in Beryl maintaining tropical cyclone status when it moves across the Lesser Antilles on Sunday. Even though Beryl is expected to dissipate just east of the Lesser Antilles early next week, the remnant tropical wave will continue moving quickly westward and will likely bring locally heavy rains and strong gusty winds to portions of the Leeward Islands on Sunday and Monday. Key Messages: 1. Due to its very small size, there is greater-than-usual uncertainty in the analysis of Beryl's current intensity. Confidence in the official intensity forecast is also much lower than normal. Rapid changes in intensity, both up and down, that are difficult to predict are possible during the next couple of days. 2. While Beryl is still expected to dissipate as a tropical cyclone by Monday before reaching the Lesser Antilles, there will likely be some rain and wind impacts on those islands early next week. Residents there should monitor products from their local weather office for more information. FORECAST POSITIONS AND MAX WINDS INIT 06/0300Z 10.4N 44.0W 55 KT 65 MPH 12H 06/1200Z 10.7N 45.5W 60 KT 70 MPH 24H 07/0000Z 11.2N 47.4W 65 KT 75 MPH 36H 07/1200Z 11.9N 49.7W 65 KT 75 MPH 48H 08/0000Z 12.7N 52.5W 60 KT 70 MPH 72H 09/0000Z 14.4N 59.7W 50 KT 60 MPH 96H 10/0000Z...DISSIPATED $$ Forecaster Stewart
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