Tropical Storm Alerts Issued for Puerto Rico and Nearby Islands Ahead of Developing Disturbance

Ernesto expected to form this week and strengthen into a powerhouse hurricane but turn well east of the mainland U.S.

On Sunday, the National Hurricane Center designated the strong disturbance moving through the central Atlantic Potential Tropical Cyclone Five. The procedural move was made to spur the issuance of watches and warnings for a system expected to develop into Tropical Storm Ernesto before reaching the easternmost Caribbean islands on Tuesday.

A Tropical Storm Warning is in effect for the Leeward Islands north of Dominica westward to Anguilla for the expectation of tropical storm conditions (winds of 39 mph or stronger) in the next 36 hours. Additionally, a Tropical Storm Watch is in effect for Puerto Rico and the U.S. Virgin Islands for the possibility of winds exceeding 39 mph in the next 48 hours. These watches will likely be upgraded to tropical storm warnings later Monday as the system closes in on the islands.

Air Force hurricane hunters investigating the system this morning are finding a still broad and disorganized wind field with no indications yet of the well-defined circulation needed to upgrade the system, but winds are already near tropical storm strength on the northern side. The official forecast calls for the disturbance to become a tropical depression by early Tuesday, but it could skip the depression stage and head straight to Tropical Storm Ernesto before crossing into the northeastern Caribbean Tuesday afternoon.

While wind gusts to over 50 mph will be possible on its closest point of approach to the U.S. territories early Wednesday morning, the main threat to Puerto Rico and the U.S. Virgin Islands will be threat for heavy rainfall, flash flooding, rapid river rises, and the potential for landslides and mudslides in areas of higher terrain.

Future Ernesto expected to turn east of the mainland U.S. but could threaten Bermuda

Like many of our early systems so far in 2024, the disturbance forecast to become Ernesto this week is moving as a fast clip. Its quick pace from the east is helping to impart easterly wind shear over it – an unusual departure from the more common westerly wind shear we normally see atop deep tropical systems – and stymieing short-term development prospects.

By mid-week, the developing system will reach the western edge of the Bermuda high whisking it westward and begin to slow down. As it makes a sharp right turn north of the Dominican Republic over the western Atlantic waters, more pronounced strengthening should commence and by the end of the week, Ernesto could be a powerhouse Category 3 hurricane as it curls northward in the general direction of Bermuda for the weekend.

Probability of Potential Tropical Cyclone Five or future Ernesto passing within about 100 miles of a given location based on the overnight runs of all reliable global forecast models. This combined multi-model ensemble forecast show the greater uncertainty near Bermuda by late week, but also gives us confidence that the system will not pose a direct threat to the mainland United States. Credit: Tomer Burg/University of Oklahoma

It's too soon to say whether future Ernesto will pose a direct threat to Bermuda, but it will be in the vicinity of the British archipelago, so interests there should monitor the forecasts closely this week.

The late week escape route will keep future Ernesto well east of the United States but depending on how big or strong it grows, dangerous swell could reach the shoreline of the Eastern Seaboard by later this week or next weekend.

Eyes wide open for the rest of August

Though long-range models don’t currently show any looming threats behind soon-to-be Ernesto, the Atlantic will stay in a broadly conducive configuration for tropical development for the rest of the month.

Forecast areas of abnormal rising air (cooler colors) and abnormal sinking air (warmer colors) across the global tropical band from the European forecast model ensemble system. The black line indicates today’s date and everything below the line is a forecast through middle September. The map cutout on the very bottom shows the area of the globe over which we find abnormal rising air or sinking air. When the rising air branch gets “stuck” over the north Indian Ocean and Africa as is indicated in the dark shaded box, it suggests a favorable regime for tropical development in the Atlantic. This coincides with a climatologically favored time of year for hurricane development in the Atlantic, so we don’t expect any prolonged slowdown to the activity. Credit: ECMWF

As we’ve learned with recent storms, the forecast models struggle with detecting potential genesis until a system is closer to forming, so we look at the overall pattern to determine whether activity will persist or settle down beyond a week. There’s nothing right now to suggest a slowdown ahead, so we’ll keep close tabs on the tropical waves rolling off Africa and into the deep Atlantic as primetime hurricane season settles in.