American Marconi Wireless News - Major Category 3 hurricane heads for southern Mexico

"Additional strengthening is forecast, and Otis is expected to be an extremely dangerous category 4 hurricane when the center reaches the coast" by early Wednesday, it said.

"Rapid weakening will occur after landfall," it added.

Maximum sustained winds increased to near 125 miles (200 kilometers) per hour, according to the NHC, which put Otis in the third-highest category on the five-step Saffir-Simpson scale.

The storm's center was located 115 miles from the beach resort of Acapulco, and a hurricane warning was in effect for the coastline from Punta Maldonado to Zihuatanejo.

Authorities in the southern state of Guerrero suspended school classes and prepared to open emergency shelters.

Soldiers were seen patrolling the beach of Acapulco, where visitors made the most of the calm before the storm.

"We won't be running any tours today," tourist boat operator Carolina Torres said, voicing hope that Otis might weaken before making landfall.

"If it hits us, that's very serious for us," she added.

Rainfall of up to 15 inches (38 centimeters) was expected across Guerrero and parts of neighboring Oaxaca state, the NHC said.

"This rainfall will produce flash and urban flooding, along with mudslides in areas of higher terrain," it warned.

Hurricanes hit Mexico every year on both its Pacific and Atlantic coasts, usually between May and November.

Earlier this week, Tropical Storm Norma left three people dead, including a child, after making landfall for a second time in the northwestern state of Sinaloa.

Norma came ashore for the first time on the Baja California peninsula on Saturday before heading back out to sea and barreling into the mainland.

Earlier this month, two people died when Hurricane Lidia, an "extremely dangerous" Category 4 storm, struck the western states of Jalisco and Nayarit.

And in August, storm Hilary, which at one point was also a Category 4 hurricane, caused one death and damaged infrastructure as it hit the northwestern state of Baja California.

Scientists have warned that storms are becoming more powerful as the world gets warmer with climate change.

P.Stevenson--AMWN