Summer 2023 broke dozens of daily and monthly heat records » Yale Climate Connections

Dozens of all-time daily and monthly records melted from Arizona to Florida this summer during one of the hottest stretches in U.S. history, a disaster cataloged in the national climate summary for summer 2023 released by NOAA on Monday. Many folks from Detroit to Boston experienced a summer near or slightly cooler than average, but that didn’t comfort others across rapidly growing Sun Belt states. For many of them, the period from June to August was a brutal ordeal, their hottest three-month stretch ever endured.

Averaged across the contiguous 48 U.S. states, summer 2023 was the 15th-hottest in 129 years of record-keeping, according to NOAA. Louisiana saw its hottest summer on record, and it was a top-10 hottest in six other states, as shown in Figure 1. No state had a top-10 coolest summer on record.

The heat last month was particularly brutal across the Gulf Coast states from Texas to Florida. Persistent drought and light winds allowed the coastal plains and the adjacent Gulf waters to roast to unprecedented levels, in many cases topping record August averages by 2 degrees Fahrenheit or more. Three states saw their hottest August on record — Florida, Louisiana, and Mississippi — and it was a top-10 hottest August in eight other states, extending to Oregon and Washington, as shown in Figure 2. No state had an August that was significantly cooler than average. Averaged across the contiguous 48 U.S. states, summer 2023 was the ninth-hottest in 129 years of record-keeping, according to NOAA.

Read: The fight to protect Miami’s outdoor workers against the deadly heat

The month was slightly wetter than average nationally but quite dry along the Gulf Coast. Louisiana had its driest August on record, and Mississippi and Texas were in their top-10 driest, while 10 states from California to Maine had a top-10 wettest August.

Below is a summary of cities in the contiguous U.S. that had their all-time hottest month in August and/or experienced their hottest summer overall, as compiled by weather historian Christopher Burt. Note that several cities with more than a century of weather data had their hottest month on record this past July, then promptly broke that record the next month.

Outside the 48 contiguous states, the extreme Atlantic heat was reflected in Puerto Rico, where San Juan tied its hottest summer in 124 years of record-keeping (85.1°F) and experienced its hottest August on record (85.2°F, toppling 85.0°F from 1980). In a much different marine setting, Utqiagvik, on the Arctic coast of Alaska, had its “warmest” summer in 102 years of record-keeping (43.2°F, beating the 42.9°F in 1989).

“Winners” and “losers”

This summer’s standout combination of a large population and incredible monthly heat was in Phoenix, where the July average of 102.7°F was the first to exceed 100°F for any month in any major U.S. city. Maricopa County, which includes Phoenix and which has become a national leader in tracking and analyzing heat mortality, reported 194 confirmed heat-related deaths as of September 6, with 351 other deaths under investigation. At least 80 unhoused people in Maricopa County have died from heat-related causes this year; at least 40 others lost their lives in structures where the air conditioner was not working.

Read: For unhoused people in America’s hottest large city, heat waves are a merciless killer

Across the Midwest and Northeast, much of the summer wasn’t scorching but was instead tepid and acrid — the result of periodic intrusions of thick smoke from record-smashing forest fires across Canada, including those in and near Quebec that one analysis found were made twice as likely by climate change. In New York City’s Central Park, which had near-average readings for summer as a whole, nights tended to be warm while days averaged on the mild side. From June through August, only six days in New York hit 90°F, and readings in August never got above 88°F, a lack of heat that’s happened in August only 10 times in 155 years of data.

When global heating hits home

There were clear fingerprints of human-induced climate change on the southern U.S. heat waves, which mirrored similar bouts of record heat across many of the globe’s land areas and oceans over the past three months (see our global roundup coming on September 14). One example: As we reported last month, it was the hottest July on record for Arizona, Florida, and New Mexico (as well as Maine) The World Weather Attribution initiative reported that “maximum heat like in July 2023 would have been virtually impossible to occur in the U.S./Mexico region and Southern Europe if humans had not warmed the planet by burning fossil fuels.” And the nonprofit Climate Central found that people in a number of U.S. cities experienced at least one day of heat in July that was made at least three times more likely by climate change.

The Maui fire and Hurricane Idalia

There were two billion-dollar U.S. disasters in August:

• A catastrophic wildfire decimated the historic community of Lahaina, Maui, in a matter of hours on August 8. The fire took more than 100 lives, making it the deadliest U.S. wildfire in 105 years. The blaze damaged or destroyed more than 2,000 structures (mostly homes), and rebuilding costs were estimated at more than $5.5 billion. The fire was driven by fierce, dry winds blowing downslope from the West Maui mountains. This setup is similar to the Santa Ana or Diablo mountain winds that have caused fire catastrophes in California; in this case, the winds were forced by unusually strong high pressure to the north of Maui, perhaps exacerbated by the indirect effects of Hurricane Dora far to the south. The growth of nonnative vegetation across Hawaii in recent decades has also been cited as a contributing factor.
• Hurricane Idalia vaulted to Category 4 strength over the record-warm waters of the eastern Gulf of Mexico on August 29-30, then weakened to Category 3 strength just before striking the Big Bend area of the Florida Gulf Coast on the 30th. Idalia was the strongest hurricane to strike the Big Bend area north of Cedar Key and east of Apalachicola in NOAA records dating back to 1851. Idalia’s small size and its short life as a Gulf hurricane helped minimize the breadth of its impact apart from the immediate, hard-hit Big Bend. Insured damages were estimated between $2 and $5 billion, unusually low for a major U.S. landfall (total damages are typically twice the insured value). Idalia led to at least seven direct and three indirect fatalities.

Jeff Masters contributed to this post. Website visitors can comment on “Eye on the Storm” posts (see comments policy below). Sign up to receive notices of new postings here.