Hurricane Amanda began weakening on Monday and was not threatening land, but it remained a powerful Category 4 storm far off Mexico's Pacific coast.
The hurricane's maximum sustained winds Monday morning were near 135 mph, down from a peak of 155 mph on Sunday, making it the most powerful May hurricane since the mid-1960s, when reliable records began to be kept.
The US National Hurricane Center said rapid weakening is expected over the next two days.
The hurricane was centered about 680 miles south of the southern tip of Mexico's Baja California peninsula and was moving north-northwest near 5 mph.
While hurricane Amanda was forecast to stay out to sea, Mexico's National Meteorological Service said rains associated with the storm were likely to drench much of western and central Mexico.
Mexico's national civil protection authorities urged people living near the coast to keep an eye out for swelling rivers and potential mudslides in mountainous areas, and to listen to broadcasts about the storm's location and possible effects.
The Eastern Pacific hurricane season officially started May 15. The Atlantic hurricane season starts June 1.
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