Hurricane Carlotta strengthens off Mexico Pacific coast

* Hurricane Category 1, seen picking up force

* Pacific oil refinery not affected

* Storm far south of Los Cabos hosting G20 summit

By Mica Rosenberg

ACAPULCO, Mexico, June 15 (Reuters) - Hurricane Carlotta formed in the Pacific on Friday and strengthened quickly on a path headed to Mexico's southern coast, the U.S. National Hurricane Center said.

Carlotta, the third named storm of the Pacific hurricane season, had maximum winds of nearly 85 mph (137 kmh) with higher gusts. It was about 90 miles (145 km) south-southeast of Puerto Angel and about 285 miles (460 km) southeast of the tourist city of Acapulco at 2 p.m. EDT (1800 GMT).

The center said it expected "rapid strengthening" in the Category 1 storm later in the day and that it could become a Category 2 as it neared the coast. It was expected to make landfall later in the day or early Saturday.

The Mexican government issued a hurricane warning from Punta Maldonado to the tourist resort of Acapulco. Guerrero state officials said they had an emergency plan in place, including two temporary shelters. In Acapulco, it was sunny and cloudless Friday afternoon with some winds.

State oil company Pemex took preventative measures but by late Friday morning, the eye of storm had passed north of its biggest refinery, the 330,000 barrel-per-day Salinas Cruz. It said the installation was operating normally.

The hurricane's path also is far from the Baja California resort of Los Cabos, where the Group of 20 leaders of top economies are convening on Monday and Tuesday. Authorities said they did not expect Carlotta to make much of an impact and that the airport remained open.

It was sunny and cloudless on the highway into Acapulco, and there was some wind, Reuters witnesses said.

Oaxaca state weather officials reported moderate to heavy rainfall in southern Mexico. State officials said they hadn't yet ordered residents to evacuate or to suspend schools.

It said it expected a dangerous storm surge and significant coastal flooding in the area.

Officials said the hurricane could dissipate if it moved over the mountains of southern Mexico. They predicted a prolonged period of heavy rain in the area.

In 2002, Hurricane Kenna hit south of Los Cabos while the city was hosting an international meeting of the 21-member Asia Pacific Economic Cooperation group. Strong winds from Kenna knocked over the main tent at the event where world leaders were set to attend a gala dinner. No one was injured.

Kenna hit land 300 miles (482 km) south of Los Cabos in 2002. Carlotta is expected to strike the coast more than twice as far away.