Atlantic/2018/02L/Archive/6

Hurricane Beryl Discussion Number 6

Wiki-Hurricanes Forecast Center

11:00 AM AST Fri Jul 5 2018

Three is a pocket-sized hurricane and among the smallest observed in the satellite era, with the central dense overcast of the storm spanning just 40 miles in diameter. The eye that emerged last night in Beryl continues this morning on all conventional satellite channels, with a defined -55°C eyewall cloud top ring around the eye. Three is small enough such that even high-resolution microwave imagery is failing to sample the miniscule core structure well, though a 1206Z 37GHz GMI microwave pass appeared to faintly observe an eye at the low-levels of the atmosphere, resolutely confirming that the eye is a true eye and a deep-layer structure. Three also features some banding features in all quadrants except the northwest, though given the hurricane's small size these bands are not particularly intense. A small patch of dry air seen on visible channels is positioned in the circulation's northeast, but is fairly miniscule and is being washed out by a bolstered northern eyewall this morning and afternoon. Observing the eye, both SAB and TAFB have estimated T4.0/65kt for Three on visible and infrared methods. Automated infrared intensity estimates have failed to accurately identify the center, so these are being discarded. UW-CIMSS AMSU gave 73kt +/- 12kt on data from 0713Z. On the basis of structural improvements in the last six hours to the system of the core and an intensifying eyewall, the intensity estimate for this advisory has been raised to 70 kt. Using Knaff-Zehr-Courtney on the storm parameters yields a pressure of 994 mb.

Three continues to track south of model guidance despite consistent attempts by statistical models to show a straightforward west-northwest heading. They have however shifted south in response to the southerly position of Hurricane Three. Because of this shift, the Windward Islands are now as implicated in Three's future as much as the Leeward Islands are. A general west to west-northwesterly motion should continue under the influence of subtropical ridge for the remainder of the forecast period. The current forecast philosophy has not changed and is on the southerly edge of statistical track guidance.

Of course the big question mark with Beryl is intensity which holds the key to potential impacts and track particularly later in the forecast. The conditions within which Three finds itself are expected to be favorable out to at least 24 hours, with shear remaining under 10 kts with the aid of an anticyclone which is helping to push back against the unfavorable southwesterly flow east of the Lesser Antilles. Deep-layer thermal differential atop generally 27°C waters is now at a very favorable 82°C which should continue to support convective activity. LGEM, SHIPS, HWRF, and HMON all feature a high-end Category 1 hurricane at peak intensity all around tomorrow morning. Global guidance has generally failed to resolve Three well save for the GFS, so unfortunately only their environmental parameters can be taken as valid. After tomorrow, shear is expected to increase as Three begins to encounter a tropical upper-tropospheric trough which could impact Three with 20-30 kt wind shear. Surprinsgly, quality-controlled model guidance keeps a consolidated tropical storm reaching the Lesser Antilles despie southeasterly wind flow. Looking at parent domains, it is evident that many are insistent in the ability for the upper-level anticyclone to deflect the upper-level flow north of the system, though conditions will be quite dry by then. Intensification is depicted to 24 hours, with most strengthening probably taking place in the overnight and morning hours accounting for diurnal processes, with the system tapering off out in day 2 before weakening more quickly and dissipating in the eastern Caribbean.

FORECAST POSITIONS AND MAX WINDS

INIT 06/1500Z 70 KT 80 MPH

12H 07/0000Z 75 KT 85 MPH

24H 07/1200Z 80 KT 90 MPH

36H 08/0000Z 80 KT 90 MPH

48H 08/1200Z 70 KT 80 MPH

72H 09/1200Z 45 KT 50 MPH

96H 10/1200Z 45 KT 50 MPH ... REMNANT LOW

120H 11/1200Z ... DISSIPATED