The US National Hurricane Centre in Miami said the main body of the category-4 hurricane poses little threat to land, however.
It was centred about 1,240 kilometres south of the southern tip of Baja California and forecasters said it was likely to start weakening while staying well out to sea, at least through Friday.
Even so, Mexico's National Meteorological Service said rains associated with Amanda were likely to drench much of western and central Mexico.
The Eastern Pacific hurricane season officially starts on May 15. The Atlantic season starts on June 1.