A ‘heat dome’ is back over Texas. Here’s what that means (and why it’s the worst).

Last year was a lot. It was the second-hottest summer in Texas.

Much of that heat is because, well, Texas is hot as all get-out. Not just some get-out. It’s hot as all get-out. But last year, we thought, was novel: a pressure system, formally known as a heat ridge, crept up from the South and parked a mass of heat and humidity over much of the state. Non-science folks call the stiflingly cruel phenomenon a heat dome.

Turns out, last year wasn’t so novel.

Texas is facing similar conditions now. Some South Texans are already feeling the heat dome’s effects. Folks in Central Texas are staring down that oppressive mass as it inches northward.

You’ve probably got questions. What is a heat dome? Why is this happening to me? How would a seemingly benevolent Mother Earth allow such a scourge to exist, nay, thrive? We can get to some of those science-based questions. For the others, you’re on your own.

Buckle up, sweaty.

What is a heat dome?

A heat dome is a high-pressure system that, because physics, traps heat and keeps it there. That pressure system’s atmospheric energy is hard to bust up: The high pressure above is met with the rising heat below, which makes the system especially stubborn and slow-moving.

Right now, that pressure system is trapped over land, but that mass is also heating the water in the Gulf of Mexico – it’s making it hotter. Gulf waters have heated to about the same temperatures as last year. When the air from the Gulf blows to the shore, it compounds that trapped heat, saturating the air and creating the conditions under the dome.

Kim Wood is an atmospheric scientist and professor at the University of Arizona in Tucson – where denizens enjoyed a not-at-all-balmy 108 degrees last week.

“If (the heat is) trapped over land, you’re going to see higher temperatures,” Wood said, adding that Tucson gets a drier heat. “If that’s trapped over water, then those waters are going to warm up. And if the waters are warmer, that’s more moisture that can get into the air because there’s more energy.”

The persistent flow of warm air from the Gulf means things don’t really cool down overnight, so heat begets more heat when it’s under the dome.

Is this going to be worse than last year?

In short, time will tell, but the conditions we’ve seen so far? They’re eerily similar to last year, according to Victor Murphy with the National Weather Service.

“What is that ridge of high pressure gonna do this year? Is it gonna stay in place? Or will it build northward into Texas like it did last year? And if it does build northward into Texas like it did last year,” he said, “I don’t want to think about it.”

So far, Murphy said, South Texas has seen record-breaking high temperatures in both Brownsville and Del Rio – not by hundredths or tenths of a degree, by a lot more.

“They usually might beat it by half a degree and maybe, at most, 1 degree,” he said. “So to see 120-, 150-year records shatter by 2 to 3 degrees is pretty significant. It shows you the magnitude and the strength of this heat ridge.”

He said that heat ridge isn’t likely going to break up, and it could creep farther northward. Last week, San Antonio saw a record heat index of 117, a sign that it could be slowly making its way to Central Texas.

Austin is preparing for a hotter-than-normal summer. So far, EMS calls for heat-related illnesses are up 90 percent, compared to this time last year. Officials are particularly concerned about people experiencing homelessness.

Still, Murphy said, it’s not likely this summer will be as bad as last year, which brought 45 days straight of triple-digit heat.

But given the current conditions and global warming, Murphy said, this summer could be among the top 20 warmest on record.

If that sounds like good news, it speaks to how conditioned we’ve become to extreme heat over the last few decades.

What does this mean for hurricane season?

Again, time will tell.

The Gulf of Mexico is exceedingly warm, and yes, water temperature is a key factor in the formation of hurricanes.

But that doesn’t guarantee an active hurricane season, Wood stressed.

“There’s always the chance for an active hurricane season, but most storms stay out to sea,” they said. “So an active hurricane season does not mean an active landfalling season.”

Water temperatures aren’t the only factor for hurricane formation – or landfall.

Changes in wind speed and direction, the amount of water in the air, atmospheric conditions, distance from the equator and “seed disturbances” – which can be a thunderstorm or some other pressure system – can all create a tropical cyclone. That tropical cyclone could turn into a hurricane. Or it could break up over open water.

But, Wood said, if a hurricane does find itself in the Gulf, those warm temperatures could strengthen it, while also causing it to stay parked much like the heat dome is now. That’s what happened with Hurricane Harvey in 2017.

“As we’ve seen so many times, it just takes one storm,” Wood said. “I’m hoping nobody gets that one storm.”

Mose Buchele contributed to this story.

This story was produced as part of the Austin Monitor’s reporting partnership with KUT.

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