Tropical storm Dora is expected to intensify as it moves through the Pacific Ocean off the coast of Mexico and will likely become a hurricane Tuesday night.

This map from the U.S. Hurricane Weather Centre in Miami shows the expected path of Tropical Storm Dora, which is forecast to become a hurricane later Tuesday. (CBC)

The U.S. National Hurricane Center in Miami said Tuesday that the storm was about 395 kilometres southwest of Puerto Angel, Mexico, and 475 kilometres south-southeast of Acapulco, Mexico, with maximum sustained winds of 110 km/h. The storm is forecast to head west-northwest, nearly parallel to the coast of southwestern Mexico, as it intensifies.

A tropical storm becomes a hurricane when its maximum sustained winds reach 119 km/h.

Dora could become a major hurricane by early Thursday, the weather centre said, with tropical storm force winds extending up to 205 kilometres from the centre.and making surf conditions dangerous for southern Mexico.

There are no coastal watches or warnings in effect yet in the U.S.

Tropical storm Bret, meanwhile, was in the Atlantic about 535 kilometres south of North Carolina, but was expected to weaken and avoid land.