Willa began as a tropical storm but rapidly intensified into a hurricane in the eastern Pacific and will threaten later this week.
The National Hurricane Center (NHC) said Willa is expected to become a major hurricane by Monday morning.
Major hurricane status could mean at least Category 3 intensity.
Hurricane Willa was tracking westward but it will curve toward the northwest on Sunday, bringing it on a path towards Mexico.
The NHC said: “A turn toward the north-northwest and north is expected by late Sunday and Monday.
“Willa is expected to accelerate toward the northeast and approach the coast of west-central mainland Mexico by late Tuesday.”
The hurricane is packing maximum sustained winds to near 85mph (140km/h) with even higher gusts and “rapid strengthening” is forecast.
As the hurricane is located in an area of low wind shear and very warm water temperatures, this will spur Willa on and drive its intensity.
AccuWeather senior meteorologist Paul Walker said: “Willa will continue moving into an environment conducive for rapid strengthening and can become a major hurricane by midweek.”
However an increase in wind shear will lead to weakening as it approaches land.
Downpours began to graze southern Mexican coastlines on Saturday evening, but torrential rain will continue into Monday and could trigger flash flooding and mudslides across western and southwestern Mexico.
The regions of Mexico most at risk would be those near Willa’s landfall.
Willa is expected to make landfall on Tuesday night or Wednesday in Nayarit or southern Sinaloa.
The hurricane could make landfall potentially as a Category 1 or Category 2, with winds up to 81mph (130km/h).
There is even a risk of a storm surges for those living on the southern edge of the hurricane’s eye.
“The more widespread impact will be tropical rainfall, which can lead to flooding and mudslides, even away from the coast,” Mr Travis added.
Willa has the potential to leave a portion of these areas without power for days after landfall.
Meanwhile, the eastern Pacific is also active with Tropical Storm Vicente.
However because of its small size and its projected track, Vicente is expected to become absorbed by Willa by late next week.
Willa is likely to remain stronger than Vicente and will disrupt the tropical storm enough to keep it from reaching hurricane status.
Tropical storm Vincent, Hurricane Willa and what was once Tropical Storm Tara have boosted the 2018 Eastern Pacific hurricane season to become the most active on record.
As of October 20, there have been 22 named storms, 12 of which became hurricanes and nine of which were major hurricanes – at least Category 3 intensity – in the Eastern Pacific Basin in 2018.