SAN JUAN, Puerto Rico -- Government leaders ordered schools, airports and even casinos to close and they prepared shelters as Tropical Storm Erika approached the eastern Caribbean on Wednesday.

The storm was located about 250 kilometres east of Antigua and was moving west at 28 kph with maximum sustained of 75 kph. The storm was not expected to strengthen over the next two days.

Erika was forecast to pass near Antigua and Barbuda overnight, with authorities in the twin-island nation warning of flash floods given the extremely dry conditions caused by the worst drought to hit the Caribbean in recent years.

Boats at Shell Beach Marina on Antigua's north coast have been out of the water since Saturday, with people not taking chances as Erika approaches, said Caroline Davy, a marina employee.

She said many people were caught off-guard when Tropical Storm Gonzalo battered Antigua last October.

"Too many times we've seen things happen that were not predicted," she said.

Authorities in the nearby Dutch Caribbean territory of St. Maarten said schools and government offices would close Thursday. They also asked that casinos, restaurants and other businesses close by midnight Wednesday. Officials warned they might temporarily suspend power and water service as the storm approaches.

The U.S. National Hurricane Center said Erika would move over or near parts of the Leeward Islands late Wednesday and then near Puerto Rico and the Virgin Islands on Thursday.

All airports in the U.S. Virgin Islands would be closed to incoming flights until Friday, and government offices would close as well, said Gov. Kenneth Mapp.

"This is a fast-moving storm, and so we expect conditions to deteriorate rapidly," he said.

Tropical storm warnings were issued for Puerto Rico, the U.S. and British Virgin Islands and the Leeward Islands. A tropical storm watch was in effect for the northern Dominican Republic, the Turks & Caicos Islands and southeastern Bahamas.

The storm is expected to be near South Florida by Monday, according to James Franklin, chief hurricane forecaster at the National Hurricane Center in Miami. But its intensity is still uncertain.

"We don't know how much of the storm will be left," he said, adding that it faces strong upper-level westerly winds in the next two to three days.

Antigua-based regional airline LIAT and Puerto Rico-based Seaborne Airlines have cancelled more than two dozen flights through Friday because of the storm, and officials in Puerto Rico said they would suspend ferry transportation between the main island and the popular sister islands of Culebra and Vieques starting Thursday. The U.S. Coast Guard said it would close all ports in Puerto Rico and the U.S. Virgin Islands on Thursday. Universities across Puerto Rico also announced they would not hold classes on Thursday.

Meanwhile in the Pacific, Tropical Storm Ignacio gained some strength. The storm's maximum sustained winds increased to 100 kph, and it was expected to strengthen to a hurricane by Thursday.

Ignacio was centred about 2,195 kilometres east-southeast of Hilo, Hawaii, and was moving west at 19 kph.

Associated Press reporter Judy Fitzpatrick in Philipsburg, St. Maarten contributed to this report.