MIAMI -- Tropical Storm Joaquin has strengthened slightly as it continues to drift to the west over the Atlantic, CBS Miami reports.

At 11:00 a.m. on Tuesday, maximum sustained winds had increased to 45 mph with higher gusts.

Joaquin formed in the Atlantic on Monday, becoming the 10th named storm of the season, while Hurricane Marty ambled toward the south-central coast of Mexico in the eastern Pacific.

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The U.S. National Hurricane Center in Miami said that Joaquin was centered 400 miles northeast of the central Bahamas late Monday. It was moving southwest at 5 mph. There were no coastal watches or warnings in effect, but the center said the storm was expected to strengthen during the next couple of days.

In the eastern Pacific, Hurricane Marty was moving slowly toward the south-central coast of Mexico hours after forming Monday, bringing heavy rains from Zihuatanejo to Acapulco.

Late Monday, Marty was centered about 75 miles southwest of Zihuatanejo and about 140 miles west of Acapulco. The hurricane had maximum sustained winds of 75 mph and was moving northeast at 3 mph.

A hurricane watch was in effect for Tecpan de Galeana to Lazaro Cardenas. A tropical storm warning was in effect from Acapulco to east of Tecpan de Galeana, and a tropical storm watch was in effect from west of Lazaro Cardenas to Punta San Telmo.

The Hurricane Center said Marty was expected to be just offshore of the southwestern coast of Mexico on Tuesday and Wednesday, while "only a small deviation" would bring the center onto shore. Forecasters also warned of significant coastal flooding.