Puerto Rico and nearby islands on alert for Ernesto

The large tropical disturbance trekking toward the Northeast Caribbean—officially tagged Potential Tropical Cyclone Five by the National Hurricane Center—is slowly getting organized. A large cluster of thunderstorms on the northwest side of the broad system might be where the center actually forms, but it's going to take a little longer for the system to consolidate.

Slightly hostile upper winds are slowing the process, but the ocean water is exceptionally warm, so this isn't a question of whether Tropical Storm Ernesto is going to form. It's only a question of where or when.

In case a closed circulation develops that includes winds of 40 mph or higher before it reaches the islands, Tropical Storm Warnings are in effect from Guadeloupe to the north in the northeastern Caribbean. Tropical Storm Watches are in effect for the Virgin Islands and Puerto Rico because it will take longer for the system to reach that vicinity.

There is also some question when possible-Ernesto will turn north. Some computer model forecasts show the system beginning its turn just east of Puerto Rico. It's too close to call, at least until an organized system actually forms.

Everybody in Puerto Rico and the islands of the northeast Caribbean should stay well informed. The forecast track will likely jump around a bit as the system organizes.

The strong consensus of the computer forecasts, as reflected in the National Hurricane Center's forecast cone, is that likely-Ernesto will turn north in the general vicinity of Puerto Rico or the Virgin Islands. Only the Southeastern Bahamas and the Turks and Caicos should stay alert because the edge effects of possible Hurricane Ernesto could affect that area.

There is no threat to the East Coast of the U.S. from Florida to the Northeast except for high waves and dangerous surf late in the week and over the weekend. There is some chance of a greater impact in New England about a week from now, depending on how sharply likely-Hurricane Ernesto turns out to sea. Stay informed from Cape Cod to DownEast Maine.

Residents of Bermuda will have to watch for adjustments in likely-Ernesto's forecast as well. The storm will be in their general vicinity over the weekend or early next week.

One of the factors slowing the storm's development is Saharan dust, although the system is pulling enough moisture from the south to counteract the fairly thin dust cloud covering the waters east of the islands.

The dust is much denser farther east, however. That should keep the next batch of African disturbances from developing for at least the next week or so.