The governments of Sinaloa and Nayarit states ordered coastal region schools to close on Monday and began preparing emergency shelters ahead of the onslaught.
A hurricane warning has also been issued for Mexico's western coast between San Blas and Mazatlan.
"Willa is forecast to accelerate toward the north-northeast and move over or very near the Islas Marias early Tuesday and make landfall along the southwestern coast of mainland Mexico in the hurricane warning area late Tuesday or Tuesday night", according to the NHC.
Hurricane force winds extended out 40km from the storm's core and tropical storm force winds were up to 130km out.
The storm is expected to weaken when it makes landfall Tuesday but is forecast to bring large waves, unsafe storm surge, gusty winds and heavy rain.
Willa is expected to reach category 5 status on Monday - the highest classification for hurricanes.
As of the NHC's latest advisory at 12.00am local time (7am BST) Hurricane Willa was located approximately 195 miles south-southwest of Cabo Corrientes, Mexico.
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Later in the day, authorities in Guatemala said another group of about 1,000 migrants had entered that country from Honduras. Passing freight trucks were quickly boarded by dozens of migrants, and straining tuk-tuks carried as many as a half-dozen.
"Willa is moving toward the north near 7 miles per hour (11 km/h), and this general motion is expected to continue today".
The hurricane centre estimates that total rainfall will range between 5 inches and 15 inches across stretches of Jalisco, Nayarit and Sinaloa states, home to Mexican white sand beach resorts of Puerto Vallarta and Mazatlan.
Some areas could see up to 18 inches of rainfall, likely triggering flash flooding and landslides in mountainous areas.
Willa is then expected to weaken after passing over the Sierra Madre mountains, and the remnants of the storm will likely will bring significant rainfall to Texas.
Its core was about 230 miles (370 kilometers) southeast of Acapulco with top sustained winds of 40 mph (65 kph). Afterward, weakening is forecast, and Vicente is expected to become a tropical depression by tonight or Tuesday.
The Hurricane Center said it could produce 3 to 6 inches (7.5 to 15 centimetres) of rain near the coast.