From the state of Texas to Florida, about 35 million people in the US are bracing for a widespread heat wave which is expected to last for days, the National Weather Service (NWS) said in its latest forecast.
The heat wave in parts of Texas, Louisiana and Florida is likely to break records and raise the risk of wildfires and heat-related illnesses, Xinhua news agency reported citing the forecast issued on Thursday.
"It wouldn't be an active summer weather pattern without oppressive heat and much of Texas and the Deep South will have plenty heading into the beginning of the holiday weekend," the NWS added.
Record-setting June heat wave is building up in many parts of Texas.
The Dallas-Fort Worth area in northern Texas is forecast to see heat index readings of 40 to 44 degrees Celsius on Thursday or Friday, the weather service said, adding that high temperatures in the area could hit triple digits by early next week, earlier than average to the region.
In Austin, the capital city of Texas, the hottest June 14-20 period is on record with an average high temperature of 40 degrees over the next week, the First Warning Weather team predicted.
A new tool developed by the Climate Central, known as the Climate Shift Index, attributes the heat wave to manmade climate change by showing fingerprints of climate change on day-to-day weather at a particular location.
According to Climate Central's analysis, Austin's high temperatures by Thursday afternoon exceeding 37 degrees were at least five times more likely because of climate change.
Later this week or early next week, the heat index in southern and western Texas could climb up as high as 48 degrees, according to the NWS, warning health risks for people working outdoors or living indoors without air conditioning.
Amid the heat wave, electricity demand is expected to rise in Texas, the second most populous state in the US, later this week, the Electric Reliability Council of Texas which manages about 90 per cent of the state's electricity load, said in a statement.
However, power supply will be enough to meet the demand and an "energy emergency" is not expected, said the council.
A heat advisory was also put in effect from 11 a.m. through 7 p.m. on Thursday in the coastal state of Louisiana.
Though high temperatures were forecast to stay in the mid and upper 90s, the high humidity will make it feel like 40 to 43 degrees and it will feel even hotter in the direct sun, experts said.
Temperatures are expected to climb into the upper 90s to potentially the lower 100s in parts of Louisiana, but heat index values will be between 108 and 115 degrees due to the humidity over the weekend and potentially into next week.
The weather service on Wednesday issued a heat advisory for most of South Florida as the heat index in the area was projected to reach values from 40-43 degrees daily through Tuesday.
The NWS usually issues a heat advisory in a 12-hour window before the onset of extreme or dangerous heat conditions.
The rule of thumb for issuing a heat advisory is typically when the maximum heat index temperature for the day is anticipated to reach 40 degrees or higher.
According to the NWS, parts of Arizona, New Mexico and Texas were expected to experience critical fire weather on Thursday and Friday.
The weather service also warned of the chance of strong thunderstorms and possible tornadoes for the southern US region.
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