The contiguous US just recorded its hottest summer in 132 years of measurements

The average temperature across the contiguous United States this summer topped every one of the previous 131 summers on record, according to the National Centers for Environmental Information. Meteorological summer, defined as June through August, averaged 74.4 degrees Fahrenheit, edging past the prior marks set in 1936 and 2021 by four-tenths of a degree. August itself set its own record, averaging 75.6 degrees, about 3.5 degrees above the 20th-century average for the month.

How August Pushed the Season Past 1936 and 2021

NCEI’s national climate summary, published September 9, tracks temperature and precipitation data back to 1895, giving meteorologists a 132-year baseline for comparison. Daytime maximum temperatures for August averaged 88.6 degrees nationwide, also a record for the month. The agency’s rankings treat both August and the full June-through-August season as the warmest in that entire record, not just among recent decades. Most of the country experienced above- to much-above-average August readings, with only parts of the northern Plains and Midwest holding near normal conditions. NCEI’s full August climate report, with county-level detail and a complete list of record setters, is due for release September 14, five days after the national summary that established the seasonal record.

Record Heat Concentrated Across the Southwest

California, Nevada, New Mexico and Colorado each logged their warmest August on record for statewide average temperature. California and New Mexico additionally recorded their warmest average daytime highs, while nighttime lows reached record warmth in California, Nevada, Arizona, Utah and Colorado. The pattern extended back through the whole season: Arizona tied its warmest summer on record, and New Mexico, Utah and Colorado each logged their own warmest summer. Southern Florida also saw widespread record-breaking warmth in August, showing the heat was not confined to the arid Southwest alone. Summer-long, much-above-average nighttime minimum temperatures spanned most of the contiguous United States, even in places where daytime highs stayed closer to normal, a pattern that pushed up the overall seasonal average without necessarily producing record-breaking daytime heat everywhere.

A Dry, Hot August Compounded the Numbers

Precipitation across the contiguous U.S. averaged 2.30 inches in August, 0.32 inch below the 20th-century average and enough to rank in the driest third of the 132-year record. It was the driest August nationally since 2000. Texas and Oklahoma each received less than 30 percent of their typical August rainfall, their lowest statewide August totals since 2000 as well. The dry conditions compounded the heat in the southern Plains and Lower Mississippi Valley, where soil moisture losses under sustained high temperatures tend to reinforce each other, a feedback that climatologists point to when a hot month also runs unusually dry. California’s summer precipitation totaled just 0.20 inch, only 26 per cent of its typical seasonal average, making it the state’s fifth-driest summer on record and its driest since 2002. Across the full June-through-August season, the contiguous United States received 8.11 inches of precipitation, 0.21 inch below the 20th-century average and also in the driest third of the 132-year record.

Hawaii’s Opposite Extreme: A Hurricane’s Rainfall

While the mainland baked, Hurricane Lala delivered the second-wettest August on record for Hawaii, with rainfall peaking at 43.54 inches at Laupāhoehoe on the Big Island. Year-to-date precipitation across the island chain ran more than three feet above the 1991-2020 average, making the January-through-August period the wettest on record for the islands. Alaska, by contrast, tracked closer to normal, with an August average of 52.4 degrees, 2.9 degrees above its 1925-2000 baseline and landing in the warmest third of its 102-year record rather than setting an outright record.

Why Some Interior Regions Missed the Extremes

Not every part of the country shared in the record warmth. Daytime maximum temperatures stayed close to average across much of the Midwest and the Ohio and Tennessee valleys through the summer, even as nighttime lows ran much above average almost everywhere else. That split, warm nights paired with near-normal daytime highs in the country’s midsection, is one reason the national seasonal average could set a record while individual states in that corridor did not. Meanwhile, Indiana and Ohio each logged their highest August precipitation on record, roughly double their typical totals, and neighboring Illinois, West Virginia and New Jersey each received more than 50 per cent above their average August rainfall. That split illustrates how sharply conditions diverged between the parched Southwest and the soaked Ohio Valley and Mid-Atlantic in the very same month that produced the record national heat average.

What the September Outlook Points To

The National Centers for Environmental Information’s August summary notes that above-average temperatures are favored for September across much of the country, from the Southwest and Rockies through the Great Lakes, Gulf Coast and Southeast, with the strongest odds centered on the southern and central Plains. The Climate Prediction Center’s 30-day outlook also favors below-average precipitation over the central Plains and middle Mississippi Valley, conditions that, layered onto an already dry and hot summer, are expected to sustain or expand drought in several of the same regions that just came through record heat. Wildland fire potential is also forecast to run above average across parts of the northern Great Basin, the southern Plains and the Lower Mississippi Valley through September.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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