More than 100 million people across the U.S. were under heat warnings on Sunday, with cities on the East Coast bracing for record-breaking temperatures as the heat dome causing the dangerous conditions expands to the West Coast.

Baltimore and Philadelphia are forecast to touch records near 100 degrees Fahrenheit (38 degrees Celsius) on Sunday, while temperatures rise into the 90s F in states like Idaho, Montana and Wyoming, as much as 15 degrees above normal for this time of year. The extreme heat will then shift to Nebraska and Kansas on Monday, the National Weather Service (NWS) said.

Officials are warning of dangerous conditions in the Philadelphia region where high humidity could drive heat indices above 105 F (41 C), making it feel even hotter than the actual temperature.

"It likely means we'll be seeing periodic periods of excessive heat across a decent part of the country into July," NWS meteorologist Marc Chenard said. "Not continuous at any one spot, but the overall pattern will continue to favour these above normal temperatures."

Temperatures have cooled in the Ohio Valley, Great Lakes and New England regions, but excessive heat in the 90s F continues to stretch from Virginia to New York.

Climate change is driving dangerous heat waves across the Northern Hemisphere this week and will continue to deliver dangerous weather for decades to come, research shows.

Extreme heat is suspected of causing hundreds of deaths across Asia and Europe as it has taken over cities on four continents. More than 1,000 have died during Haj, the annual pilgrimage to Mecca in Saudi Arabia, amid sweltering temperatures this year, according to a Reuters tally.

In New Mexico, officials are responding to multiple weather events, including a dust storm, flooding and two wildfires.

The Biden administration last week declared an emergency over the wildfires, which have been blamed for two deaths and more than 1,400 destroyed structures.

The FBI has offered a $10,000 reward for information leading to an arrest of anyone responsible for the fires. The blazes have scorched 25,000 acres (10,117 hectares) around the village of Ruidoso, according to the government wildfire tracking website Inciweb.

While excessive heat is causing problems in many states, other states are also contending with flooding.

Iowa Governor Kim Reynolds on Saturday issued a disaster proclamation covering 21 counties due to flooding from heavy rains in the northwest part of the state. Rock Valley officials on Saturday ordered some residents to evacuate with the help of the National Guard, local news outlets report.

A flood advisory is also in place in southern Minnesota and southeastern South Dakota.