Tropical storm Erika took aim at the Caribbean and storm warnings went up in Puerto Rico and in several other islands in anticipation of heavy rains, US forecasters said.

With winds of 75 kilometers (45 miles) per hour, Erika was 315 kilometers east of Antigua at 2100 GMT, the Miami-based National Hurricane Center said, warning of the potential for flash floods in places.

Advancing west, it was expected to sweep over the Lesser Antilles islands Wednesday night and then near the Virgin Islands and Puerto Rico Thursday, and the north coast of the Dominican Republic on Friday.

There were storm warnings in a dozen Caribbean islands but Erika's strength was not forecast to change significantly in the next 48 hours, the NHC said.

Nevertheless, several islands were due for extremely heavy rain that could spark flash floods, especially in mountainous areas in drought-parched Puerto Rico and the Dominican Republic.

In Haiti, which lies just west of the Dominican Republic on the island of Hispaniola, authorities warned locals to expect Erika's wrath off the north coast Friday or Saturday.

The impoverished country is vulnerable even to non-hurricane force winds and heavy rains.

Many homes are rickety at best and thousands are still living in emergency housing after a devastating 2010 earthquake that killed more than 250,000 people and crippled the nation's infrastructure.

Erika is arriving on the heels of Danny, the season's first hurricane, which petered out before reaching the Caribbean.

Experts said earlier this month that there was a 90 percent chance the 2015 hurricane season in the Atlantic would be less active than usual.