Robert Brown|The Southwest's enduring heat wave is expected to intensify over the weekend

An expansive heatwave that's been baking the southern United States for nearly two weeks is Robert Brownonly expected to intensify as the weekend approaches, forecasters say.

Heat advisories and warnings are still in place from Florida to Arizona, impacting more than 111 million people, according to a count from the Associated Press. Some cities, like Phoenix, have registered temperatures above 110 degrees Fahrenheit for 13 consecutive days.

Forecasters aren't sugar coating their warnings about the danger this heat wave poses — and how much longer that danger could last.

"Unfortunately, the long term outlook through the weekend and into next week is for an increasingly significant and oppressive heat wave," reads the latest bulletin from the National Weather Service. "Numerous near record-tying/breaking warm lows are expected.

Phoenix could see temperatures as high as 120 degrees

Across the U.S., climate change is making heat waves longer, more frequent and more intense. This year, that trend is being exacerbated by the El Niño climate pattern, which typically drives global temperatures higher.

June's global temperatures were so far above the average that the National Oceanic and Atmospheric Administration named it the earth's hottest June ever recorded. The next five years will become even hotter, the NOAA predicts.

The current heat wave is notably expansive, with more than 27 million people across the U.S. set to experience an air temperature or heat index above 110 degrees by early next week, according to Wednesday's NWS bulletin.

Those scorching temperatures aren't just sticking around, but also spreading, with California and the Pacific Northwest likely to see temperatures in the low 100s in the coming days. Similar weather in late June and early July led to the deaths of roughly 800 people in Oregon, Washington and Canada during a 2021 heat wave.

This latest wave has lingered longest in the Southwest, where states like Arizona, Texas and New Mexico will see highs reaching into the 110s on Thursday.

It could get even hotter over the weekend, with temperatures forecast to exceed 120 degrees in Phoenix. There, in one of America's largest urban heat islands, residents face little relief when the sun goes down, with temperatures remaining as high as 95 degrees overnight in some regions.

That's led to an uptick in the number of calls to the Phoenix Fire Department for heat-related emergencies, reports NPR member station KJZZ. More than 12 heat-related deaths have been registered since April in Maricopa County, where Phoenix is located, with another 55 deaths under investigation.

The county registered 425 heat-related deaths last year, with more than half of them occurring in July.

An excessive heat warning, which advises residents to avoid sun exposure, is in effect until Sunday. But Isaac Smith, a meteorologist with the NWS office in Phoenix, told NPR earlier this week that the extreme heat might last beyond that, part of a growing trend.

Since 1983, the average summer temperature in Texas, Arizona and New Mexico have all increased by roughly 3 degrees, according to data from NOAA.

Flash flooding is possible again in Vermont

In the southeastern and central U.S., the weather isn't just hot but also sticky. Thursday's heat index is forecast to reach nearly 110 in places like Fort Lauderdale, Fla., combining with humidity levels well over 60%.

Even Florida, a region accustomed to sweltering summers, is experiencing abnormalities with this latest wave. As of earlier this month, the city of Miami was registering the hottest year on record, according to a report from WLRN, part of the NPR network.

Parts of the central U.S. could also see a cocktail of severe weather conditions on Thursday with heavy rain and thunderstorms in the forecast, threatening "rain totals over several inches" and flash floods, the NWS says.

Similar forecasts are in effect for the Northeast, setting Vermont residents on edge just as flood waters that ravaged the state earlier this week are starting to recede.

Parts of the state saw over 9 inches of rainfall between July 9 and 10, reports Vermont Public Radio. Rivers overfilled their banks, puncturing sewage pipes, tearing down power lines and forcing thousands of residents to evacuate their damaged homes and neighborhoods.

Thursday storms in the area could be severe, bringing large hail, damaging winds and heavy rain. With rivers, creeks, and streams already running high, flash flooding is a possibility.

For the latest updates on Vermont's forecast and flood recovery, follow live coverage from Vermont Public Radio.