May 20, 2024 - Energy & Environment

Central America's heat wave helped spark Houston's deadly derecho

Map showing unusually strong heat dome parked over southern Mexico on May 23.

Computer model projection of an unusually strong heat dome over southern Mexico on May 23. Image: Weatherbell Analytics

The storm that killed at least four people in Houston and barreled through New Orleans into northern Florida late last week has ties to a record-shattering, relentless heat wave anchored over Central America.

Why it matters: With extreme weather events, particularly in this era of rapid climate change, seemingly disparate events thousands of miles apart can be closely connected, with one triggering or intensifying another.

Zoom in: During the past several weeks, a powerful area of high pressure aloft, or heat dome, has parked itself over Mexico and occasionally spun southeastward, over the Yucatán.

  • It has led to scorching temperatures across the region, with monthly and all-time temperature records falling in Belize, Guatemala and Mexico, where concerns are rising over Mexico City's diminishing water supplies.
  • The heat dome's northern reaches have brushed up against the U.S., with record heat enveloping South Texas and highly populated areas of Florida from Tampa to Miami.

By the numbers: The formation has helped to cause already hotter-than-average ocean temperatures across the Caribbean Sea and Gulf of Mexico to increase further, raising temperatures of adjacent land areas even more in a positive feedback loop.

  • Key West, Fla., for example, has set records for hitting a heat index of nearly 115°F, while Miami saw its third-highest heat index reading on record Saturday, with all of the other historical records occurring during July and August.
  • Miami's heat index on Saturday hit 112°F, the highest on record for the month of May, crushing the previous milestone by 5°F.
  • It equaled that on Sunday, which was only the second time two back-to-back days with such high heat and humidity had occurred there (the other instance was in August of last year.)

Between the lines: Around the edges of heat domes, complexes of severe thunderstorms often erupt. They are triggered by atmospheric disturbances, as well as heat and moisture to the south clashing with cooler and drier air to the north.

How it works: The grouping of severe thunderstorms was classified as a derecho for its long-lasting wind damage.

Yes, but: The heat dome can best be considered a macro-level contributor to the Houston calamity.

What's next: The heat dome shows no signs of abating, along with its effects in South Florida and Texas. In fact, it may expand to more areas of the U.S., including nearly all of South Texas and into the Southern Plains this week.

  • In a May 17 NWS forecast discussion, meteorologists stated of Florida's sizzling temperatures, "Unfortunately, this pattern looks to continue not only into next week but into the following week as well."
  • On Sunday, both Key West and Miami were under NWS heat advisories, which is unusual for so early in the season.

Context: Heat extremes are becoming more common and severe as human-caused climate change becomes more pronounced.

  • Climate Central's Climate Shift Index, which measures climate change's influence on day-to-day weather, found that Sunday's forecast temperatures in Miami were at least 5 times more likely to occur as a result of human-caused global warming.

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