The NHC said, with maximum sustained winds of 120 miles per hour, Bud is now moving northwest at about seven miles per hour.
"Even though Bud is now a powerful hurricane, it is going to pass over ocean waters of progressively decreasing heat content", the center said.
The National Meteorological Service issued a forecast at 7:00am for intense storm conditions in Nayarit, Jalisco, Michoacán, Colima, Puebla, Chiapas and Oaxaca. Rainfall of 3 to 6 inches (75 to 150 millimeters), with isolated patches of 10 inches (250 millimeters), was possible into Tuesday afternoon.
Torrential downpours could cause "life-threatening" flash floods, mudslides and waves along coastal areas in Mexico, the NHC said.
Forecasters said Bud was expected to strengthen further before a slow weakening trend starts Tuesday. The storm peaked on Friday as a Category 4 hurricane with winds of 140 miles per hour.
The hurricane is moving north-west at about 10mph - a course it is expected to take until mid-week, the NHC said.
Hurricane Bud has grown to a category four hurricane but is still expected to get weaker as it approaches Mexico and the Southwestern United States, the National Hurricane Center's latest advisory says.
For the season as a whole, three to six tropical cyclones are predicted for the central Pacific hurricane basin, which includes tropical depressions, named storms and hurricanes.
Two major category 5 hurricanes, Irma and Maria, ploughed through the Gulf of Mexico, the Caribbean and the USA west coast during 2017's extremely active Atlantic storm season, leaving a trail of destruction in their wake.
Maximum sustained winds were 195 kilometers per hour.