Invest 95L quickly developed into Tropical Storm Don Monday afternoon east of the Windward Islands, continuing the fast start to the 2017 Atlantic hurricane season. An Air Force Reserve Hurricane Hunter identified a small but well-defined low-level circulation. Don is the fourth named storm of the 2017 Atlantic hurricane season; the average date for the formation of the fourth named storm is not until August 23.  In the Eastern Pacific, Invest 97E has developed into Tropical Depression Seven-E, which has a chance to develop into Tropical Storm Greg.

Forecast for Don

As of 8:00 p.m. EDT, Tropical Storm Don was centered near 11.2°N 53.8°W and was moving westward at about 17 mph. Maximum 1-minute sustained winds were 45 mph with an extrapolated minimum pressure of 1009 mb, based on the latest aircraft data. Don currently consists of a ball of deep convection that has been bursting during the past few hours, with the center located right underneath the convection. Don has a chance to strengthen slightly during the next 24-36 hours before wind shear increases over the Caribbean Sea. A Tropical Storm Warning has been issued for Grenada, and a Tropical Storm Watch is in effect for Barbados, St. Vincent and the Grenadines, and St. Lucia.

During the next 24-36 hours, Don is expected to be in an environment with sea surface temperatures near 28°C (82.4°F) and wind shear less than 10 knots. However, by Wednesday, wind shear is expected to begin to increase, and this should probably cause the small cyclone to dissipate by Thursday. The NHC only expects slight strengthening with Don, but based on its current structure, I think it could strengthen to a moderate to strong tropical storm as it approaches the Windward Islands. Don should dissipate over the central Caribbean.

East Pacific remaining active, system behind Don could develop

The East Pacific remains very active today. Hurricane Fernanda is still a category 3 major hurricane, but is likely to weaken soon and is expected to become a remnant low before reaching Hawaii. In addition to Fernanda, a sheared Tropical Depression Seven-E developed over the Eastern Pacific today, and is expected to only strengthening due to marginally favorable conditions. Invest 98E in the East Pacific could also develop, and the National Hurricane Center (NHC) gives this system a 60 percent chance of development over the next 48 hours before encountering increasingly unfavorable conditions. Another area of low pressure is likely to form south of Mexico late this week, and the NHC gives this system a near zero percent chance of development within 48 hours and a 30 percent chance within five days. The next East Pacific names are Greg and Hilary. It is not expected that Seven-E or 98E will be any threat to land.

An area of low pressure in the Atlantic east of Tropical Storm Don also has a low chance to develop into a tropical cyclone this week. NHC gives this system a 20 percent chance of development within 48 hours, and a 30 percent chance within five days. The next name on the Atlantic naming list is Emily.

I will be back tomorrow for an update on all of these systems.