Jul 10, 2023 - Climate

Heat wave may be the longest ever and temperatures will likely increase

Illustration of the hot emoji as a sun.

Illustration: Shoshana Gordon/Axios

The excessive heat warning that hit Phoenix on June 30 is likely to continue into next week and become the longest heat wave on record, according to the National Weather Service.

Threat level: Phoenix will break the record 18-day streak of 110-plus-degree days if the heat wave continues through July 18 — which is well within the realm of possibility, NWS meteorologist Gabriel Lojero tells Axios Phoenix.

  • "It appears as an exaggeration, but unfortunately based on what we're seeing ... It's just an extremely high-confidence forecast. It's very important that people take this seriously. Heat is a very serious thing, and you better not let your guard down," Lojero says.

Why it matters: 425 people suffered heat-associated deaths in metro Phoenix last summer. Unhoused, elderly and chronically ill people are more likely to die or be hospitalized because of heat.

  • A recent study predicted half of Phoenix residents would need emergency medical attention if a multiday blackout were to coincide with a heat wave.
A map of forecasted temepratures.
Photo: Courtesy of Climate Prediction Center

What's happening: A high-pressure system is sitting directly over the Valley, keeping temperatures high and heat-relieving storms away, Lojero tells Axios Phoenix. Temperatures are likely to increase throughout this week as the heat dome intensifies.

  • Moisture is forecasted to increase this week, but not enough to trigger precipitation. Instead, the moisture will actually increase overnight temperatures and keep low temperatures in the 90s, he said.

What's next: NWS extended the excessive heat warning through Sunday, but Lojero says it could persist even longer.

The big picture: Climate change has led to longer, hotter and more frequent heat waves around the world, including in the Southwest.

  • Four consecutive days last week broke or tied records as Earth's hottest day since at least 1940 and likely far longer, according to National Oceanic and Atmospheric Administration data.
  • Last month was the globe's warmest June, also since at least 1940, and the month shattered records for the warmest global sea surface temperatures.

Be smart: Drink water constantly, wear light, loose-fitting clothes and avoid strenuous outdoor activities from 10am to 6pm. Have a plan in case of an AC outage.


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