Hurricane Jova has made landfall in the Mexican state of Jalisco as a Category 2 storm.
The US National Hurricane Centre says Jova's maximum sustained winds early today were near 100mph with steady weakening expected as the storm moves inland.
Jova is centred about 65 miles west-northwest of Manzanillo and is moving north-northeast.
As the storm's leading rain bands began pounding the coast on Tuesday night, heavy rain fell in the port city of Manzanillo and strong winds made palm trees sway.
Meanwhile, Tropical Storm Irwin regained some strength further out in the Pacific with winds near 45mph.
While it is expected to move eastward toward land, forecasts indicate it probably won't make landfall.
Jova is expected to weaken to a tropical storm while crossing the coastal mountains and heading over western Mexico today.
The The US National Hurricane Centre warned that the storm surge could cause significant coastal flooding along the 210-mile stretch between Manzanillo and Cabo Corrientes, which is south west of the resort city of Puerto Vallarta.
Up to 20 inches of rain could fall on isolated areas as Jova moves inland, the centre said.
Before nightfall yesterday, marines visited flood-prone areas in Manzanillo to advise people to leave. They found a home for elderly people already flooded and evacuated 37 residents to the homes of relatives, Admiral Jaime Mejia said. Forty others were evacuated in the nearby town of Tecoman, he said.
Some people vowed to ride out the storm, while others took refuge at shelters in towns like Jaluco, just inland from the beach community of Barra de Navidad.
Jalisco state authorities evacuated about 200 people to shelters by Tuesday and issued alerts over loudspeakers placed in communities along the coast, telling people to take precautions as the hurricane approached, state civil defence spokesman Juan Pablo Vigueras said. The state had 69 shelters ready, he said.
Authorities also set up shelters for residents of inland towns, where the mountainous terrain could cause flash floods and mudslides, which often pose the greatest dangers in hurricanes.
The Mexican army said it had assigned about 1,500 soldiers to hurricane preparedness and relief efforts.
Jova is expected to hit the states of Jalisco, Colima and Nayarit the hardest. About 183,000 people live in the centre of the storm's projected path, said Laura Gurza, chief of the federal Civil Protection emergency response agency.
Authorities shut down Manzanillo's port, the biggest cargo centre on Mexico's Pacific coast, and the nearby port of Nuevo Vallarta.
The hurricane is expected to be dissipating by the time the Pan American Games start on Friday in nearby Guadalajara.