According to the National Oceanic and Atmospheric Administration (NOAA), Hurricane Willa is “expected to produce life-threatening storm surge, wind and rainfall”.
The areas most at risk are west-central and southwestern Mexico, with heavy winds and rainfall also threatening the US state of Texas.
At 9am MDT (4pm BST) on Monday, the huge storm was churning about 135 km southwest of Cabo Corrientes, Mexico.
Willa is packing maximum sustained winds of 160 mph, and is churning across the Pacific at 7 mph.
The hurricane is forecast to accelerate toward the north-northeast and move over the Islas Marias early on Tuesday.
The troubling storm is due to make landfall along the southwestern coast of mainland Mexico in the hurricane warning area on Tuesday afternoon.
Slight weakening is forecast to begin on Tuesday, but Willa is expected to be an “extremely dangerous major hurricane when it reaches the coast of Mexico,” said NOAA.
NOAA is warning of extremely dangerous storm surge is likely along portions of the coast of southwestern Mexico by Tuesday, especially the centre of where Willa makes landfall.
Near the coast, the surge will be accompanied by large and destructive waves.
Willa is expected to produce storm total rainfall accumulations of six to 12 inches, with local amounts to 18 inches, across portions of western Jalisco, western Nayarit, and southern Sinaloa in Mexico.
This rainfall will cause life-threatening flash flooding and landslides, NOAA warned.
Farther inland, Willa is expected to produce rainfall amount of two to four inches across portions of Zacateca, Durango, southeast Chihuahua, and Coahuila in Mexico, with local amounts to six inches possible.
Hurricane conditions are expected within the hurricane warning area on Tuesday afternoon, with tropical storm conditions expected by Tuesday morning.
Large swells generated by Willa will continue to affect portions of the coast of southwestern and west-central Mexico during the next few days.
These swells are likely to cause life-threatening surf and rip current conditions, warned NOAA, and residents in the area are advised to heed official warnings.
Moisture from Hurricane Willa will produce at least three inches worth of rain in South Central Texas, The National Weather Service has said in its latest update.
The meteorological agency tweeted: “Moisture from now Category 5 Hurricane #Willa in the eastern Pacific will produce heavy rain across Texas this week.
The following areas are under advisory:
A Hurricane Warning is in effect for:
* San Blas to Mazatlan, including Las Islas Marias
A Hurricane Warning means that hurricane conditions are expected somewhere within the warning area within the next 36 hours.
Preparations to protect life and property should be rushed to completion.
A Tropical Storm Warning is in effect for:
* Playa Perula to San Blas
* North of Mazatlan to Bahia Tempehuaya
A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area, in this case within the next 12 to 24 hours.