MEXICO CITY (Reuters) -Storm Beatriz formed off Mexico's Pacific coast on Thursday and will likely strengthen into a hurricane by Friday, prompting the government to issue warnings for popular beach resorts as it heads near shore, the National Hurricane Center (NHC) said.

The storm is expected to "move very near or along the coast of southwestern Mexico" and is moving west-northwest near 12 mph (19 km/h),the U.S.-based NHC said late Thursday.

"Beatriz is likely to become a hurricane on Friday," the NHC said.

Mexico's government issued a hurricane watch from the Playa Perula to Cabo Corrientes in Jalisco state, with planned closure of ports in the area for small vessels.

A tropical storm warning is also in effect from Punta Maldonado in the southwestern state of Guerrero, home to tourist hotspot Acapulco, to Zihuatanejo, another popular beach town in the state.

Maximum sustained winds were blowing near 40 mph (65 kph). Through Sunday morning, rainfall between 3 and 7 inches (7.5 to 18 cm) is expected across southern Mexico from the state of Oaxaca to Jalisco, which could lead to flash flooding, the NHC said.

Swells were also forecast along Mexico's southwestern coast, likely to cause life-threatening surf and rip current conditions.

(Reporting by Cassandra Garrison and Isabel Woodford; Editing by Mark Porter and Cynthia Osterman)