Roughly 130 million people in the U.S. were under threat Saturday and into next week from a long-running heat wave that already has broken records with dangerously high temperatures – and is expected to shatter more from East Coast to West Coast, forecasters said.

Oppressive heat and humidity could team up to spike temperatures above 38 degrees Celsius in parts of the Pacific Northwest, the Mid-Atlantic and the Northeast, said Jacob Asherman, a meteorologist with the National Weather Service.

In Oregon, records could be broken in cities including Eugene, Portland and Salem, Asherman said. Dozens of other records throughout the U.S. could fall, Asherman added, causing millions to seek relief from the blanket of heat in cooling centers from Bullhead City, Arizona, to Norfolk, Virginia.

The National Weather Service said on Saturday it was extending the excessive heat warning for much of the Southwest into Friday.

By 10:30 a.m. on Saturday, the National Weather Service said the temperature already had risen to 36.6 degrees Celsius in Phoenix, which saw a record high of 47.7 degrees Celsius for the date on Friday.

"A dangerous and historic heat wave is just getting started across the area, with temperatures expected to peak during the Sunday-Wednesday timeframe," the National Weather Service in Las Vegas said in an updated forecast.

In Santa Barbara County, the so-called Lake Fire scorched over 49 square kilometers of grass, brush and timber. Firefighters said the blaze was displaying "extreme fire behavior" and had the "potential for large growth" with high temperatures and low humidity.

The worst was yet to come across much of the West, with triple-digit temperatures likely – between 8 and 16 degrees Celsius higher than average into next week, the National Weather Service said.

The Eastern U.S. also was bracing for more hot temperatures. Baltimore and others parts of Maryland were under an excessive heat warning, as heat index values could climb to 43 degrees Celsius, forecasters said.