Tropical Storm Don has formed east of the Windward Islands. A small circulation formed within a broad trough Monday afternoon, identified by an Air Force reconnaissance mission. The recon plane found winds of about 45 mph as of the 8pm AST NHC advisory. While the circulation was originally associated with only limited convection, a strong convective burst has formed over the center of the system during the last few hours. Whether this burst is strengthening Don or not will likely be hard to tell until the next recon mission Tuesday morning. Given the small size of Don’s circulation, the storm could easily strengthen or weaken in a short period of time. Environmental conditions ahead of Don are favorable in the short term, with SHIPS diagnostics indicating that shear will remain below 10 kt until Tuesday evening, and Don’s circulation is still isolated from the dry SAL air mass to the north. Thus, it would not be surprising to see some intensification of Don on approach to the Windward Islands on Tuesday, but the official NHC forecast from Monday evening expects little strengthening for now. A Tropical Storm Warning has been issued for Grenada, and Tropical Storm Watches for St. Vincent and the Grenadines, Barbados, and St. Lucia. After entering the Caribbean, Don’s small circulation will likely struggle to maintain itself within strong trade winds north of South America, and weakening and eventual dissipation is expected by late Wednesday. However, tropical storm conditions could potentially impact some southern Caribbean islands before that occurs. Please see the latest NHC advisory at hurricanes.gov for the latest watch and warning information.
Potential Tropical Cyclone Three is gradually becoming better organized in the central Gulf of Mexico. The surface circulation has become well-defined, and convection is beginning to take on a curved-band appearance to the NE of the center. However, strong southwesterly wind shear continues to keep the storm lopsided, with the majority of wind and rain occurring well north and east of the center. Rainfall has already begun along the north gulf coast, and will continue over the next couple of days. This heavy rain will be the primary impact of PTC3 along much of the gulf coast. Due to the aforementioned shear, PTC3 is not expected to strengthen much over the next couple days, but will likely acquire sufficient convective organization to be classified as a subtropical or tropical cyclone.
The system is currently interacting and partially merging with a mid-level low over the NW Gulf of Mexico. This low tilts NW with height, and the upper-level low remains just off the upper Texas coast. PTC3 is not expected to move fully beneath the upper low, thus moderate SW shear is expected to remain over the system until landfall along the TX or LA coastline sometime on Thursday. Due to growing proximity of PTC3 to the upper low, convective heating beneath the PV anomaly may cause shear to lessen some just before landfall. Some slight intensification is possible at that time, but the system is not currently expected to have enough time prior to landfall to take full advantage of it. The now robust low-level circulation is expected to become more symmetric, with moisture and potentially tropical storm-force winds wrapping around to the western semicircle. Thus, although most impacts currently remain north and east of the center, by the time of landfall, impacts may extend both to the east and to the west of the storm center when it crosses the coast.
Tropical Storm Bret, after forming SE of Trinidad yesterday, is now moving into the SE Caribbean just off the coast of Venezuela, and maintains and organized appearance, although the effects of southwesterly shear are beginning to manifest. This shear will increase over the next day or so, and is likely to eventually cause the dissipation of Bret in a couple of days. Until that time, however, Bret may bring tropical storm conditions to the southern Caribbean islands, perhaps as far west as Aruba, Bonaire, and Curacao. A tropical storm warning remains in effect for a portion of the Venezuelan coastline and Margarita Island.