Image source, Getty Images

Millions of Americans are under heat advisories as of Monday, but the excessively hot weather is not the only thing authorities in the US are worried about.

The National Weather Service is also forecasting other bouts of "unsettled weather" early this week, including excessive rainfall that may trigger flash flooding in parts of southern Louisiana and Arizona, the Ohio Valley and the northern mid-Atlantic states.

The US had already seen excessive flooding over the weekend, which killed five people on Saturday in eastern Pennsylvania. Two children - a baby and his two-year-old sister - remain missing.

Along with the heavy rain, forecasters also note that Canadian wildfire smoke has returned to the north-eastern US, triggering smoke advisories in cities like Cleveland, Ohio and Chicago, Illinois.

"This is possibly our new normal," New York governor Kathy Hochul warned at a press conference on Sunday.

Matt Taylor
BBC Weather

While many focus on whether absolute temperature records are broken, the crucial thing is the intensity and duration of this heatwave. This coupled with hot nights can be particularly dangerous to health.

In the US, Phoenix in Arizona will today equal its record for the number of consecutive days with the temperature equalling or exceeding 43C (110F).

Today will make it 18 days in the trot and the run may even continue until the end of next week.

El Paso, Texas, has already exceeded its previous record of 26 consecutive days reaching above 38C (100F). Today will make it 32 days.

Justin Rowlatt
BBC Climate editor, Murcia

Image source, EPA

The heat here in inland southern Spain is total. It wraps you like a blanket.

Walk even a short distance and you break into a sweat.

And this latest blistering heatwave to hit southern Europe is just beginning.

It is 35C where I am in the countryside outside the city of Murcia at the moment.

That's pretty typical for a July day here but the weather forecasters are warning us to prepare for much worse.

Scorching air from the deserts of North Africa is being swept up and across Europe. It is trapped under a high-pressure system and, just like a pressure cooker, it allows the heat to build and build.

We’ve been told to expect temperatures to rise to 40C here today and tomorrow, and as high 43C on Wednesday.

Two thirds of Spain is expecting similarly sweltering temperatures and already face special heat warnings.

The area just to west of where I am, around the city of Cordoba, is expecting more than 44C.

The worst thing isn’t the heat of the day, say local people, but the temperatures at night. Don’t expect it to fall below 28 or 29C, they tell me.

Image source, Getty Images

A man in his 70s was found dead in the desert on Sunday in Buckeye, Arizona, located just west of Phoenix, according to local media.

Police in the area tell local media, external that the death appears to be heat-related, though a medical examiner is working to determine the official cause of death.

The man was reportedly out on a bike ride when he had a flat tyre. He was due to meet his wife at a fire station, where she had planned to pick him up, and she then called the police around 13:45 local time after he failed to show up.

Buckeye remains under an excessive heat warning. On Sunday, temperatures in the city reached a high of 111F (44C) around noon local time.

The Centre for Disease Control in the US estimates that about 702 heat-related deaths happen annually each year, along with more than 67,000 heat-related emergency department visits.

Georgina Rannard
Climate and science reporter

A climate change expert from the University of Reading says she is finding it "very frightening" to see the real-life impacts of climate change in this current heatwave.

Prof Hannah Cloke says that last summer more than 61,000 people are estimated to have died because of heat, and this is a similar situation. "This is going to be deadly," she says.

Longer and more dangerous heatwaves are in line with what climate models predict, and she has been warning about these impacts for years.

"It's incredibly frustrating - nobody who can make a difference seems to be listening, no matter how hard you shout, or how hard you try," she says.

Europe is heating faster than many climate models predicted, she explains, adding that the science is extremely complicated.

Guy Hedgecoe
Reporting from Madrid

Image source, Getty Images

It’s already getting a little bit uncomfortable here but it’s going to get a lot more uncomfortable later on today. Temperatures further south could reach up to 44C (111.2F) and high alerts are in place.

People are just doing the best they can, trying to avoid strenuous activities where possible.

A special telephone line has been set up in the southern region of Andalusia, offering information about the heat and health - it has received thousands of calls over the last few weeks.

A heatwave can have an impact on all sorts of sectors, whether it's farming or tourism, which is so important for the Spanish economy. Spain has around 15% of its economy based on tourism.

When you have people being told not to go out, during certain times of the day, that’s not what tourists want to hear when they go down to the south of the country.

Tourists want heat but they don’t expect to see this much heat - and people collapsing in the heat could be a worry.

Image source, Reuters

Greece has seen a brief respite today as temperatures eased a bit, with a high of 36C forecast today in Athens.

The Acropolis has resumed its regular opening hours after closing down for three days during the hottest part of the day over the weekend.

Tourists had been barred from entering Greece's most popular attraction from 12:00 to 17:00 (9:00-14:00 GMT), with temperatures in Greece topping 40C.

But, a new heatwave is expected from Thursday and meteorologists warn of a heightened risk of wildfires amid strengthening winds from the Aegean Sea.

Image source, Reuters

Excessively hot temperatures can cause both heat exhaustion and heatstroke. The two are different, but the former is a precursor to the latter. For signs of heat exhaustion, here is what you should look out for:

• Feeling faint or dizzy
• Excessive sweating
• Clammy skin
• Nausea or vomiting
• Muscle cramps

On the other hand, if you or someone near you are suffering from heatstroke, the symptoms are:

• Confusion
• No sweating
• Temperature over 40C(104F) with hot, dry skin
• Nausea or vomiting
• Losing consciousness, convulsions or seizures

You can read more about the symptoms, as well as what to do if someone near you is suffering from heat exhaustion, here.

Image source, .

Image source, EPA

Just under 100 million people across the US will be waking up to extreme heat warnings on Monday morning, according to the National Weather Service, external (NWS).

Much of the heat is concentrated in the south-eastern portion of the US, from Louisiana to to Arizona to southern California. Parts of southern Florida are also under heat advisories.

Temperatures are expected to be consistently in the triple digits Fahrenheit (above 37C) until at least mid-week, especially in the desert and in the heart of Texas. Evenings are also expected to be unusually warm, offering little respite for people.

In some places, the heat is forecast to surpass previous records. Phoenix, Arizona is likely to register its hottest week ever.

Authorities are cautioning Americans to "take the heat seriously".

"Temperatures will reach levels that would pose a health risk, and be potentially deadly, to anyone without effective cooling and/or adequate hydration," the NWS says.

Heat is the leading weather-related killer in the US, the agency adds. More than 700 people are estimated to die each year from heat-related factors.

Justin Rowlatt
BBC Climate editor, reporting from Murcia, Spain

I’ve just touched down in Murcia, a city just inland from the Costa Blanca tourist resort of Alicante.

Temperatures are expected to peak at 43C, almost ten degrees above average.

We want to find out how people are coping.

The Italian Met Office has chosen evocative names for the series of heatwaves scorching southern Europe this summer.

Last week’s was dubbed Cerberus, after the three-headed dog that guards the gates to the underworld in Greek mythology.

It expects this week to be even more hellish and has named this latest heatwave Charon, after the boatman who ferries the dead to Hades.

There are warnings countries including Spain, France Italy and Greece are all likely to see temperatures above 40C in places.

Heat records are likely to tumble, according to forecasters.

The scorching blast is coming up from Africa and will hit Spain first.

Esme Stallard
Climate reporter

Extreme weather is becoming more frequent and more intense in many places because of climate change.

Even a small increase to average temperatures makes a big difference.

This is because the whole distribution of daily temperatures shifts to warmer levels, making hotter days more likely and more extreme.

Scientists use computer simulations, external to judge whether extreme weather events have been made more likely by warming caused by humans.

For example, a record-breaking heatwave across Spain, Portugal and northwest Africa in April was made at least 100 times more likely by climate change, external, according to the World Weather Attribution network (WWA).

Heatwaves are also becoming longer and more intense.

This can happen through "heat, external domes, external" - an area of high pressure where hot air is pushed down and trapped in place, causing temperatures to soar over large areas.

One theory suggests higher temperatures in the Arctic - which has warmed more than four times faster than the global average, external - are causing strong winds called the jet stream to slow and increasing the likelihood of heat domes, external.

• Read more here

Yesterday, the Met Office said over the weekend China had provisionally recorded its highest ever temperature in the north-western region of Xinjiang.

China's Meteorological Administration said the mercury hit 52.2C (126 F) in the village of Sanbao on Sunday.

As we've been reporting, a period of intense heat has been sweeping southern Europe, with extreme conditions expected to continue well into this week.

Here are just some photos of how the heatwave has affected different parts of the continent.

Image source, Getty Images

Image source, Getty Images

Image source, Getty Images

Image source, Getty Images

Laura Gozzi
reporting from London

Image source, EPA

I have been speaking with Giulio Betti, who is an Italian meteoroligst and climate expert. He warns summer heatwaves across Europe have become "abnormal".

"Heatwaves did happen in the 1960s, but they were episodes that lasted maybe a few days per summer, often in the middle of summers that could be either warm or cool and rainy," Giulio tells me.

"But, we don't even remember what ‘pleasant’ summers were like.

"In Italy, we have this perception that this year the month of June was pleasant and cool when it was actually the 11th hottest June since records began in the 19th Century.

"What has changed is our perception and we should be very concerned that we don't get alternate cool and hot summers any more; they're all hot, and they keep getting hotter.

"Normal summers are now a rarity and this is a global problem that doesn't have borders.”

At least 4,000 people have been evacuated from homes on the Spanish island of La Palma, as firefighters work to contain a wildfire which has burned out of control.

The fire started in the early hours of Saturday in El Pinar de Puntagorda, a wooded area in the north of the island.

People from the villages of Puntagorda and neighbouring Tijarafe had to be evacuated.

The fire has affected more than 4,650 hectares(11,490 acres) and has destroyed at least 20 homes, authorities said.

Image source, Reuters

Samantha Granville
Reporting from Las Vegas, Nevada

The usually crowded streets of Las Vegas were considerably emptier than normal on Sunday, with security guards guarding the fountains of upscale casinos and hotels to prevent people from jumping in.

Las Vegas' famous strip was a quiet inferno. Some people walked outside, but mostly just to cross the street to the next casino.

At a taco shop on the strip, the tables were all full of patrons dripping with sweat and looking utterly wiped out from the heat. Workers too were draped in the booths, not speaking to each other, but fanning themselves down.

Inside the casinos though, business continued and as the air conditioning was blasting so high people were wearing jumpers to stay warm.

The heat is set to continue for the foreseeable future, and authorities are warning that vulnerable people - including children, pregnant women and the elderly - are at serious risk of heat-related illness.

Mobile clinics report treating homeless people suffering from third-degree burns. Public buildings in some parts of California and Nevada have been turned into "cooling centres" where people can take refuge from the heat.

The heatwave in southern Europe is expected to intensify further, with 46C forecast in inland Spain today, and night time temperatures also expected to remain high.

The peak temperatures then move east on Tuesday, with parts of Sardinia likely to reach 46C and high temperatures expected across Italy for about a week.

Image source, Reuters

A heatwave is a period of hot weather where temperatures are higher than is expected for the time of year.

Experts say periods of exceptionally hot weather are becoming more frequent and climate change means it is now normal to experience record-breaking temperatures.

The European Centre for Medium-Range Weather forecasts said that globally, this June was the hottest on record.

The heatwave hitting sourthern Europe this week has been named Charon, after the ferryman who delivered souls into the underworld.

Image source, Reuters

A period of intense heat is sweeping the continent. BBC Weather says the heatwave in southern Europe will intensify over the next couple of days, with temperatures peaking on Wednesday.

• South Sardinia could see temperatures of 46C (114.8F), though most temperatures on the island will not reach those heights
• Mainland Italy is forecast highs of 43C (109.4F) in the south
• The south of Spain could also see highs of 46C (114.8F), while southern France will peak at 37C (98.6F), according to the latest forecast

There are also extreme heat warnings for the south-west of the US, with temperature records possibly being broken in 38 cities.

• Temperatures reached 116F(46.6C) in Las Vegas, Nevada, on Sunday, according to the National Weather Service(NWS) and could reach upwards of 113F (45C) later this week
• In Phoenix, Arizona, the NWS said there were highs of 115F (46.1C) on Sunday with potential record highs of 117F (47.2C) this week

Heather Sharp
Live reporter

Hello and thanks for joining us as we bring you the latest as many places around the world swelter under extreme temperatures and a changing climate.

In southern Europe and the south-west US, heatwaves are forecast to intensify in the coming days. The Italian health ministry has issued a red alert for 16 cities, the Acropolis in Athens has been closed for parts of the day after temperatures there soared to 40C and firefighters are battling a wildfire on the Spanish island of La Palma (pictured above).

In the US, a heat dome over the south-west has left millions of people under extreme heat warnings, while a temperature of 53.9C recorded in Death Valley in California yesterday.

I’m here in London where we have rain showers and a cool breeze forecast. But our reporters on the ground in southern Europe and the US, as well as our Science journalists and Weather team, are poised to bring you the latest on what’s happening, the impact and the factors driving the soaring temperatures.