As of Sunday morning, the storm had maximum sustained winds of 35 mph and was moving northwest at 8 mph.
The storm is centered about 765 miles southwest of the southern tip of the Baja California Peninsula and poses no threat to land.
Forecasters said the storm is expected to start dissipating Sunday night.
The Hurricane Center said it was the earliest formation of a tropical cyclone in the eastern Pacific since the satellite era began in 1966. The basin's season officially starts on May 15, while the Atlantic hurricane season kicks in on June 1.
According to AccuWeather, early storms in the eastern Pacific typically happen in the first half of May.
AccuWeather's top hurricane expert, meteorologist Dan Kottlowski, noted there was a lack of consistent satellite coverage over the region until 1976, which hindered record-keeping of storms that formed before the season officially began.
"Weak storms that were well removed from land, like this tropical low, were often ignored until the 1990s," Kottlowski said.
While the National Oceanic and Atmospheric Administration Climate Prediction Center will provide its initial seasonal outlook for the Atlantic basin in May, researchers at Colorado State University are predicting an above-average hurricane season this year, citing the likely absence of El Niño as a primary factor.
Forecasters are predicting 16 named storms, of which eight are forecast to become hurricanes and four to reach major hurricane strength with winds greater than 111 mph. The Atlantic hurricane season last six months, ending in November.
The Associated Press contributed to this report.