Hurricane Bud grew to Category 3 force off Mexico's Pacific coast on Monday. It's centered about 235 miles (380 kilometers) southwest of Manzanillo, Mexico, and is moving northwest at 10 mph (17 kph).
Forecasters said Bud was expected to strengthen further before a slow weakening trend starts Tuesday.
Bud could become the second major hurricane to develop in the eastern Pacific this year, following Tropical Storm Aletta last week. Rainfall of 3 to 6 inches, with isolated patches of 10 inches, was possible into Tuesday afternoon. "These rains could cause life-threatening flash floods and mudslides", the agency warned.
The NHC issued a tropical storm watch for Manzanillo to Cabo Corrientes, meaning tropical storm conditions are possible there over the next day.
"Significantly cooler waters around the southern tip of Baja California should reduce Bud's intensity below hurricane status before it reaches that land", the centre said. The storm peaked on Friday as a Category 4 hurricane with winds of 140 miles per hour (220 kph).