Heat engulfs US South: Forecast shows little relief; Phoenix sets heat record: Live updates

The southern tier of the U.S. continued to swelter Tuesday as temperatures and heat indexes soared above 100 degrees over a large chunk of the nation from Southern California to Florida.

In Phoenix, the "Valley of the Sun" is accustomed to extreme summer conditions, but the city set a new record Tuesday: it has now endured 19 straight days with high temperatures of at least 110 degrees, which broke a record set in 1974, the weather service said.

It's likely a historic streak beyond Phoenix's borders. No other major city among the 25 most populous in the United States has had a run of 110-degree days or 90-degree nights longer than Phoenix, weather historian Christopher Burt of the Weather Company told the Associated Press.

Meanwhile, heat warnings and advisories were in effect for more than 90 million Americans as record-breaking temperatures swept across the South with little relief in sight.

The National Weather Service said record highs were possible from the Four Corners states and Texas to the Lower Mississippi Valley and South Florida.

"Stay indoors and seek air-conditioned buildings," the weather service warned. "Drink water, more than usual, and avoid dehydrating alcoholic, sugary or caffeinated drinks."

America's red-hot summer: How people are coping with extreme heat waves across the country

In Los Angeles, all excessive heat warnings and advisories were canceled "as temps cooled today below critical thresholds," the weather service said. But forecasters said renewed warnings were likely for the next round of heat expected later this week into the weekend.

The Desert Southwest and Texas can expect consistent daytime highs in the triple digits, and temperatures on the Gulf Coast and in the mid-South should reach the mid- to upper 90s – with humidity combining to push the heat index to 105-115 degrees, according to the weather service.

Despite a recent weak cold front, the Northeast and mid-Atlantic will also continue to see hot and humid conditions through Tuesday.

The silver lining: Air quality that has been hovering in the danger zone in parts of the U.S. for days was improving Tuesday. The only U.S. city in the "unhealthy for sensitive groups" zone was Washington, D.C., according to iqair.com.

Next week's weather forecast map shows little relief

Unfortunately, very little in the way of heat relief is on the way next week across the country, according a forecast released Tuesday from the Climate Prediction Center. In fact, every portion of the U.S. – except for Washington state – is forecast to see above-average temperatures from July 24-28, the CPC said. The areas where unusually warm weather is most likely include most of the Southwest, the Rockies and the Great Plains, which appears as a huge swath of red on the map.

Much of the East should also see warmer-than-average temperatures, but the likelihood isn't as high, the CPC said. Only Washington state is forecast to see below-average temperatures next week.

'Insidious danger': Heat waves don't seem scary, and that's why they're so deadly

'Nothing like it has ever been seen before' in Miami

Miami has also seen some extraordinary heat recently, with meteorologist Brian McNoldy saying in a tweet Tuesday that "nothing like it has ever been seen before."

McNoldy, of the University of Miami, was referring to some "unprecedented" heat records for the city. This included the fact that the heat index in Miami has been 100 degrees or higher for the past 37 consecutive days, which is a record, he told Axios.

How to keep dogs cool: Tips to keep your pup cool without air conditioning

U.S. heat index map

Air quality alerts throughout Northern High Plains, Midwest, Great Lakes and Northeast

Smoke from the Canadian wildfires will continue to reach the Lower 48 states on Tuesday, but air quality was improving. Smoke concentrations appeared to be clearing over parts of the U.S., but the respite could be brief and subject to the vagaries of the winds.

Canada continues to endure the nation's most extensive wildfires on record − an area about the size of Kentucky is on fire.

Keep your pets safe during the heat wave

Experts are also reminding Americans about pet safety during this extreme heat, including warnings about walking your pet: "As a general guideline, if the outside temperature is too hot for you to comfortably place your hand on the asphalt for several seconds, it is likely too hot for your pet's paws as well," Dr. Alejandro Caos, a veterinarian with The Vets, said in an emailed statement.

Caos said that asphalt can absorb and retain heat, which makes it significantly hotter than the surrounding air temperature. In hot weather, asphalt can reach temperatures that can cause burns and discomfort to your pet's paw pads. Here are some general temperature ranges to keep in mind:

• 77 to 87 degrees: Generally safe for most pets.• 88 to 92 degrees: Caution advised. Keep walks shorter and avoid prolonged exposure.• 93 degrees and above: It is generally considered too hot for pets to walk on asphalt. Prolonged exposure at these temperatures can lead to burns and heatstroke.

"If you need to take your pet outside during hot weather, try to do so during cooler parts of the day, such as early morning or late evening when the ground is cooler," Caos said. "Alternatively, you can use pet booties or walk on grass or shaded paths to protect their paws from the hot surface."

Heat-related emergencies more than triple as El Paso area sizzles under high temperatures

The number of El Pasoans suffering heat-related emergencies has more than tripled this summer compared with a year ago as the region swelters under an unyielding heat wave, a fire department spokesman said Monday.

Residents are urged to take precautions as an excessive heat warning continues in the El Paso-Juárez area with temperatures forecast to possibly reach 110 degrees this week. El Paso is normally at about 96 degrees at this time of year.

El Paso hit a new record-high of 109 degrees on Monday, breaking the old daily record of 106 degrees set in 1980, the local office of the weather service reported.

On Sunday afternoon, a dozen fire trucks and ambulances were dispatched to help several people experiencing heat-illness symptoms at a car show and concert at Ascarate Park in El Paso, said the city's fire department spokesman Enrique Dueñas-Aguilar.

– Daniel Borunda, the El Paso Times

Tropical Storm Calvin weakening before reaching Hawaii

Tropical Storm Calvin, now downgraded from a hurricane, will further weaken as it approaches the island of Hawaii, the Central Pacific Hurricane Center reports. The state's Big Island has a tropical storm warning in effect until Wednesday, when the system is expected to become a tropical depression.

The Big Island can expect heavy rainfall locally with 4 to 7 inches on windward slopes and possible rough waves. Maui and Hawaii counties are under a flood watch from Tuesday evening until Wednesday afternoon, according to Hawaii News Now.

Tropical Storm Calvin: Here's what to expect on Big Island and more

Tropical Storm Calvin watches and warnings

Europe enveloped in record heat

Officials warned residents and tourists packing summer Mediterranean destinations to stay indoors during the hottest hours Tuesday as the second heat wave in as many weeks hit the region. In Italy, Red Cross teams checked on the elderly by phone, while in Portugal they took to social media to warn people not to leave pets or children in parked cars.

The temperature Tuesday soared to 109 degrees at one location in Rome, which is a record for the city, reported weather historian Maximiliano Herrera. Sicily rocketed up to 115 degrees, which is the hottest temperature reported in Europe so far this year, Herrera said.

The U.N. weather agency said temperatures this week in Europe could break the continent's all-time heat record of 119.8 degrees, set in Sicily two years ago. The World Meteorological Organization said it is stepping up efforts to strengthen heat-health early warnings as global temperatures soar.

Thunderstorms to engulf parts of Midwest and East

Heavy and excessive rainfall were expected Tuesday over the Northeast as a cold front comes from the west. Portions of the Ohio Valley have higher risks of excessive rainfall on both Tuesday and Wednesday. While the Plains and Ohio Valley have lower chances of severe weather Wednesday, residents near the Illinois/Missouri border can expect some of the heaviest rainfall, according to the weather service.

Heavy rainfall forecast in Midwest

Air quality index basics: How it works, what each color code means and how to stay safe

U.S. air quality index

Contributing: The Associated Press

This article originally appeared on USA TODAY: Heat wave expands across Southwest, Gulf Coast; forecast and updates