Willa is expected to make landfall on Mexico's south-western coast on Tuesday and is "potentially catastrophic", the National Hurricane Center (NHC) warned.
Currently a Category Four - out of five - storm, it threatens to bring torrential rains and major flooding.
Earlier this month areas of the US were devastated by Hurricane Michael, which left at least 27 people dead.
Willa is expected to deliver rainfall of up to 46cm (18in) along parts of south-west Mexico, the NHC said on Monday, as it reported that the storm was carrying winds of 250km/h (155mph).
"This rainfall will cause life-threatening flash flooding and landslides," it added.
The NHC said "an extremely dangerous storm surge" was also likely to affect coastal areas by Tuesday evening, adding that rain and strong winds would be accompanied by "large destructive waves".