The storm reached maximum sustained winds near 155 mph by 11 a.m. Sunday, making it the strongest May eastern Pacific hurricane on record.
It also set the record for earliest major eastern Pacific hurricane on record.
As of Monday, the weakened Amanda was traveling northward over the eastern Pacific Ocean.
Warm ocean waters and a lack of strong wind shear contributed to the unusually strong hurricane, Accuweather reported.
Meteorologists predict a busier-than-normal hurricane season this year due to the presence of El Nino.