A satellite image taken Tuesday morning shows Tropical Storm Erika (right) spinning east of the Caribbean.(Photo: NOAA)

Tropical Storm Erika formed overnight in the Atlantic Ocean, the National Hurricane Center said.

As of 8 a.m. ET, the storm had winds of 45 mph and was located 750 miles east of the Caribbean's Leeward Islands. It's moving to the west at 20 mph.

Tropical storm watches have been posted for several islands in the Caribbean, including Montserrat, Antigua, Barbuda, and St. Kitts and Nevis. A tropical storm watch means that tropical storm conditions are possible within the watch area, generally within 48 hours, the hurricane center said.

Erika would deliver needed rainfall to these islands, many of which are in a drought, AccuWeather said.

Though the exact track of Erika remains uncertain, the storm is forecast to move across the Caribbean, then become a Category 1 hurricane by the weekend as it spins near the Bahamas.

"All interests in the northeast Caribbean, Bahamas, Florida and the Southeast United States should closely monitor the progression of this system," AccuWeather meteorologist Dan Kottlowski said.

Erika is the fifth named tropical system of the 2015 Atlantic hurricane season. Only one of the storms, Danny, became a hurricane. Danny dissipated over the islands of the Caribbean on Monday, due to an influx of dry air and strong upper-level winds that tore the storm apart.

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