Thousands of people have been evacuated, and buildings boarded up in preparation for the potential effects of the storm in coastal towns in its path.
Hurricane Willa is making landfall as a Category 3 along the west-central coast of mainland Mexico south of Mazatlán, with destructive winds, life-threatening storm surge and flooding rainfall.
Nevertheless, the NHC warned, "Willa is expected to be a risky hurricane when it reaches the coast of Mexico".
View of the beach before the arrival of Hurricane Willa in Mazatlan, Mexico, today. It was heading north-northeast at 10 miles per hour (16 kph).
Civil defense director Luis Felipe Puente said at a televised news conference that 58 shelters had been set up for evacuees, although a lot of them took refuge with friends and relatives.
Willa was expected to bring life-threatening storm surges, rain and wind to residents on Mexico's Pacific shore, according to the US National Hurricane Center.
In a tweet Monday, Mexican President Enrique Peña Nieto said he has asked the National System of Civil Protection to take all steps necessary to protect those in the hurricane's path as well as those affected by Tropical Storm Vicente, a weaker system tracking south of Willa that's also primed to make landfall Tuesday.
Willa has maximum sustained winds of 205 kilometers (125 miles) per hour, the NHC said.
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Workers taped up windows in hotels and officials ordered schools closed in a low-lying region where towns sit amid farmland tucked between the sea and lagoons.
The federal government issued a decree of "extraordinary emergency" for 19 municipalities in Nayarit and Sinaloa states.
Forecasters said Willa would then blow ashore in late afternoon somewhere along a 220-km (140-mile) stretch from the resort city of Mazatlan to San Blas.
The hurricane was nearing the Islas Marias, a group of islands about 96 km (60 miles) offshore that include a nature preserve and a federal prison.
"It was really strong", said Cecilia Crespo, a police spokeswoman in Escuinapa, a seaside town near where the storm plowed inland.
Alberto Hernandez, a hotel worker in the town of Teacapan close to where the storm made landfall, said he and his son, who also works at the hotel, were staying on the job, though the rest of his family had left the area. American Airlines canceled all flights from Mazatlan.
Farther to the south, Tropical Storm Vicente had weakened to a tropical depression early Tuesday, but it was still bringing heavy rainfall that caused risky flooding in southern and southwestern Mexico.
It is expected to dump 15 to 30 centimeters (six to 12 inches) of rain on parts of Sinaloa, Nayarit and Jalisco states, with some areas getting up to 45 centimeters.