Chantal was about 220 miles south-southeast of San Juan, Puerto Rico, and 395 miles east-southeast of Santo Domingo, Dominican Republic and moving west-northwest at 26 miles per hour, the National Hurricane Center in Miami said in its 8 p.m. EDT advisory.
Maximum sustained winds were 65 miles per hour with higher gusts.
Chantal was expected to be near hurricane strength before reaching Hispaniola, and a hurricane watch was in effect from Barahona to Samana, Dominican Republic.
Tropical storm warnings were in effect for Puerto Rico, Turks and Caicos, the southeastern Bahamas and the entire coasts of Haiti and the Dominican Republic.
Tropical storm watches were in effect for the U.S. Virgin Islands, Vieques and Culebra, and the central Bahamas.
Chantal was forecast to gradually decrease in forward speed over the next 48 hours and pass south of Puerto Rico Tuesday night. The storm likely will be over the southeastern and central Bahamas Thursday.
Tropical-storm-force winds extended 90 miles mainly to the north of the center.
A storm surge with dangerous waves was expected to raise water levels by 1-3 feet in Puerto Rico, northern Hispaniola, the Bahamas and Turks and Caicos, and by 2-4 feet in southern and western Hispaniola.
Chantal was expected to produce 2-4 inches of rain over the Leeward and Windward Islands and 3-6 inches over Puerto Rico, the U.S. Virgin Islands and parts of Haiti and the Dominican Republic, with localized amounts up to 8 inches.