U.S. weather forecasters say Tropical Storm Hilary has formed off Mexico's Pacific coast and could strengthen into a hurricane by late Thursday.

The National Hurricane Center said in a bulletin Wednesday afternoon that the storm was 205 kilometers south-southeast of Puerto Escondido, Mexico, moving northwest with 75 kilometer-per-hour winds. Forecasters say Mexico has issued a tropical storm watch for its Pacific coast from Lagunas de Chacahua westward to Lazaro Cardenas.

Forecasters also are watching newly formed Tropical Storm Ophelia, the 15th named storm of this year's Atlantic hurricane season. In a bulletin on Ophelia, the hurricane center said the system was 1,875 kilometers east of the Leeward Islands, moving to the west with winds of 95 kilometers per hour. Forecasters say they expect it to change little in strength in the next two days.

Because Ophelia is over the open Atlantic, there are currently no coastal watches or warnings in effect.