July 2023, already recognized as Earth’s hottest month in recorded history, featured brutal heat waves that scorched America’s coastal and southern states – several of which saw their hottest single month they’d ever recorded – while the Upper Midwest and Northern Plains were surprisingly mild. For the contiguous U.S. as a whole, July ranked as the 11th warmest summer in records going back to 1895, according to NOAA’s monthly national climate report.
It was the hottest July on record for Arizona, Florida, New Mexico, and Maine. Since July is typically the warmest month of the year, the month also ranked as the warmest of any month in 129 years of recordkeeping for each of these states, as shown in the monthly averages below. The magnitude of the heat record was especially striking in Arizona and New Mexico.
- Arizona: 85.7 degrees Fahrenheit (old record 84.1°F, August 2020)
- Florida: 84.1°F (old record 84.0°F, July 2016)
- New Mexico: 78.6°F (old record 76.9°F, July 2016)
- Maine: 70.1°F (old record 70.0°F, July 1921 and July 1952)
Fifteen other states along an arc from Washington to California to Texas to Maryland to New Hampshire had their top-10-hottest July (see Figure 1 below). Most of the nation was at least a little warmer than average, while it was among the coolest third of Julys on record in Iowa, Minnesota, Nebraska, and North and South Dakota, as persistent upper-level low pressure sent a series of cool fronts through the area, keeping temperatures relatively mild.
July’s ‘ring of fire‘: All-time record heat stretches from Southern California to South Florida
All-time record heat in July afflicted not only large parts of the Sun Belt, but also several other locations far to the northwest and northeast, bookending a “ring of fire” that burned its way across the southern tier of U.S. states.
Here’s a likely incomplete list of towns and cities that broke or tied their records in July for hottest month ever recorded, in many cases beating out more than a thousand months across a century-plus of weather history. The starting year for each city’s official weather archive is labeled POR (period of record). A number of the monthly records were set by more than 1 degree Fahrenheit, which is an achievement in itself for a monthly average at a long-term weather station. The wild contrast in the record monthly averages themselves — they span almost 40 degrees Fahrenheit — is just as striking as their geographic spread. (Many thanks to weather historian Christopher Burt for helping to populate this list.)
- Quillayute, WA: 63.1°F (tied with August 2013; POR 1966-)
- Palm Springs, CA: 98.5°F (old record 97.6°F in July 2021; POR 1922-)
- Las Vegas, NV: 97.3°F (old record 96.2°F in July 2010; POR 1937-)
- Needles, CA: 101.8°F (old record 100.9°F in July 2006; POR 1888-)
- Barstow, CA: 93.4°F (tied with July 2018; POR 1944-)
- Blythe, CA: 99.4°F (old record 98.8°F in August 1969; POR 1948-)
- Flagstaff, AZ: 71.4°F (old record 70.0°F in July 2002; POR 1899-)
- Kingman, AZ: 88.5°F (old record 87.6°F in August 2020; POR 1901-)
- Phoenix, AZ: 102.7°F (old record 99.1°F in August 2020; POR 1895-)
- Tucson, AZ: 94.2°F (old record 92.0°F in August 2020; POR 1895-)
- Winslow, AZ: 83.3°F (old record 82.5°F in July 1971; POR 1915-)
- Albuquerque, NM: 85.6°F (old record 83.8°F in July 2003; POR 1892-)
- Roswell, NM: 88.1°F (old record 87.6°F in July 2020; POR 1893-)
- Eagle Nest, NM: 64.7°F (old record 63.4°F in July 2011; POR 1929-)
- Las Vegas, NM: 73.8°F (old record 72.7°F in July 2011; POR 1940-)
- Portales, NM: 84.1°F (old record 84.0°F in July 2016; POR 1905-)
- Roswell, NM: 88.1°F (old record 87.6°F in July 2020; POR 1894-)
- Socorro, NM: 85.0°F (old record 82.9°F in July 1951; POR 1893-)
- El Paso, TX: 91.6°F (old record 88.9°F in June 1994 and July 2020; POR 1887-)
- Baton Rouge, LA: 87.8°F (old record 86.3°F in August 2011; POR 1892-)
- Slidell, LA: 85.1°F (tied with July 1962; POR 1956-)
- Fort Myers, FL: 86.1°F (old record 85.9°F in June 1981; POR 1892-)
- Tampa, FL: 86.5°F (old record 86.3°F in June 2022; POR 1890-)
- Sarasota-Bradenton, FL: 86.2°F (old record 85.8°F in July 2020; POR 1911-)
- Lakeland, FL: 85.5°F (old record 85.1°F in August 1987 and July 2016; POR 1948-)
- Punta Gorda, FL: 85.8°F (old record 85.1°F in August 1951; POR 1914-)
- Winter Haven, FL: 85.6°F (tied with August 1989; POR 1941-)
- Miami, FL: 86.5°F (old record 85.9°F in July 2020; POR 1895-)
- Dry Tortugas, FL: 88.7°F (old record 87.4° in August 2011; POR 1950-)
- Key West, FL: 87.7°F (old record 87.5°F in August 2007; POR 1872-)
- Marathon, FL: 89.5°F (old record 88.0°F in June 2019; POR 1950-)
- Brunswick, GA: 87.3°F (old record 85.5°F in July 2016; POR 1944-)
- Caribou, ME: 71.5°F (old record 70.9°F in July 2018; POR 1939-)
- Dover-Foxcroft, ME: 71.4°F (old record 70.5°F in July 2018; POR 1973-)
The standout in this catalog of misery is Phoenix, where the monthly average of 102.7°F (39.3°C) smashed the prior record for any month by a phenomenal 3.6°F (2.0°C). No large U.S. city had ever before seen a monthly average top 100°F; the previous record hot month for any U.S. city was 102.2°F in July 1996 at Lake Havasu City, Arizona, according to Alaska-based climatologist Brian Brettschneider. Every day in the month but one (July 31) hit at least 110°F (43.3°C) in Phoenix. Together with June 30, the city endured a record-long streak of 31 days with highs of at least 110°F, and it also experienced a record 16-day streak in which temperatures never dipped below 90°F.
As of July 29, 39 heat-related deaths had been recorded in Phoenix’s Maricopa County, with another 312 deaths under investigation. Just as disturbingly, heat mortality records curated by the Centers for Disease Control show that the five-year running average of U.S. heat-related deaths has nearly doubled since 2010, and that’s not including this year. (See our in-depth post from 2020 on how heat fatalities are assessed.)
Along with the monthly records above, at least two U.S. weather stations with a long-term period of record set their all-time daily records in July:
- Kingman, Arizona, 114°F (45.6°C) on July 15 (old record 113°F on July 20, 2017; POR 1901-)
- Las Vegas, New Mexico, 100°F (37.8°C) on July 18 (old record 99°F on multiple dates; POR 1940-)
Death Valley, California, had the hottest temperature on the planet so far in 2023: 53.9°C (129.0°F) at Saratoga Spring on July 16. This is just short of the all-time world record for a reliably measured temperature of 54.4°C (130°F), set on July 9, 2021. (A reading of 134°F from Death Valley on July 10, 1913, which is currently shown as the world’s all-time record high, has been disputed and discounted as unreliable by multiple researchers.) Furnace Creek in Death Valley, which had 17 consecutive days with a high of at least 120°F, had its second hottest month on record in July 2023: a monthly mean temperature of 107.6°F, just behind July 2018 (108.1°F).
The non-contiguous U.S.
Record temperatures were not just recorded in the contiguous United States. San Juan, Puerto Rico had its fifth-warmest July in 125 years of record keeping, with an average of 84.6F, following its second-warmest June on record (also 84.6F). In Utqiagvik (formerly Barrow), Alaska, July was the hottest month in 105 years of data with an average temp of 48.4F (old record 48.3F from July 2019). Also in Alaska, Northway bested its previous record-warm month of 62.4°F from July 2019 with an average this July of 65.5°F.
How did the Southwest and South Florida get so hot?
As natural weather variations play out, we can expect some days, months, and years to spike above the long-term trend, which is why heat waves tend to become even hotter when they occur in a warming climate.
The subtropical belt that wraps its way around the planet at latitudes of 25-30 degrees north is notorious for sinking air, which is why many of the world’s deserts — from the Sahara in Africa to the Sonoran in North America — are located there. During July 2023, that subsidence appears to have intensified even more than usual. The resulting heat was so widespread and intense that it expanded the lower atmosphere and pushed the 500-millibar pressure surface (considered the midpoint of the atmosphere, typically at around 19,000 feet) to record-high altitudes across the nation’s southern tier. In fact, the 500-millibar surface was at record heights over most of the globe’s tropical areas as well as many parts of the subtropics, as shown in the tweet below.
The obvious place to start in analyzing July’s scorching heat across the southern United States (and many other parts of the world, as we’ll be detailing in a post next week) is long-term warming driven by fossil fuel use, which is now around 2 degrees Fahrenheit (1.2°C) globally above preindustrial values. The World Weather Attribution program concluded in a July 25 report that “maximum heat like in July 2023 would have been virtually impossible to occur in the US/Mexico region and Southern Europe if humans had not warmed the planet by burning fossil fuels.” The program estimated that such a heat wave in North America is about 3.6°F (2°C) warmer than it would have been without human-induced climate change.
Similarly, using its own attribution tool, called the Climate Shift Index, Climate Central found that “levels of July heat in the southern U.S., Mexico, Central America, and the Caribbean would have been extremely unlikely without human-caused climate change.” In many of the cities above that set all-time monthly highs, the level of heat on certain days was made four to five times more likely by human-induced climate change, according to Climate Central.
In larger cities, including Phoenix, the urban heat island is another factor exacerbating heat waves (and a heat island is a type of human-induced climate change in itself). Yet a number of smaller cities and tiny towns also set all-time records for July, as evident from the list above, so heat islands were not the sole culprit. As pointed out by the National Weather Service office in San Diego, temperatures a few miles above-ground — as inferred by weather balloon and satellite measurements — were also at record levels in July. Moreover, the all-time monthly highs listed above were set at heights above sea level that ranged from 3 feet in Marathon, Florida, up to 8,238 feet at Eagle Nest, New Mexico. Neither location would qualify as an urban heat island by any stretch.
Another factor in play: during most years the North American Monsoon brings an increase in cloud cover and rainfall across the Southwest through July. But the monsoon has been anemic this year, allowing the landscape to heat up much more readily.
Across southern and western Florida, both the atmosphere and the adjacent ocean were running at virtually unprecedented levels of heat in July. Many buoys just offshore reported sea surface temperatures above 95°F, and at Manatee Bay, the ocean surface rose to a mind-bending 101.1°F (38.4°C). Unusually light trade winds helped limit mixing just below the sea surface, allowing the paper-thin surface to heat even more than usual, as noted by Jeff Masters in a series of tweets. Organic-rich outflow from the Everglades may have also boosted the near-shore water temperatures by darkening the sea surface and thus absorbing more sunlight, he added.
The heat across South Florida also was likely enhanced in July by a lack of sun-reflecting intrusions of dust from the Sahara. And the regional and global heat in July may have gotten modest boosts from two other ongoing influences that we touched on in a July post: a drop in sun-blocking sulfur dioxide pollution from global shipping since 2020, and the undersea eruption in January 2022 of the Hunga Tonga–Hunga Ha’apai volcano, which increased the presence of water vapor (a greenhouse gas) in the stratosphere by as much as 15 percent.
Hail battered the nation yet again during a record month for severe weather
Even after a June pockmarked with hailstorm after hailstorm, July was an exceptional month for severe weather, as reported by Capital Weather Gang. The severe weather was stoked in part by a jet stream that remained stronger than usual for midsummer during much of the month. The jet has been squeezed between chilly upper-level low pressure across the Midwest and warm upper-level high pressure across the Southern Plains.
NOAA/NWS Storm Prediction Center recorded a total of 6,637 preliminary reports of severe weather, a category that includes tornadoes, hail at least one inch in diameter, and wind gusts to at least 58 mph. That’s higher than the final tally for any month in data going back to 2004. For June and July combined, the 532 reports of very large hailstones (2 inches or larger in diameter) have already broken the record of 378 that was set in 2009 for any entire meteorological summer (June through August), with one month still left to go.
As of August 9, NOAA had cataloged 15 separate billion-dollar U.S. weather disasters, which is a record for this stage of the year even after adjusting for inflation. Thirteen of these disasters were from severe weather.
The recurrent Midwestern upper lows helped give nine states a top-ten-wettest July (see Figure 2 below), including Michigan, New York, Oklahoma, Pennsylvania, and all the New England states except for Maine. For the contiguous U.S. as a whole, it was the 45th driest July out of 129 years of recordkeeping.
Drought was less widespread than it had been over the last several Julys, especially after the wet winter across the western U.S. However, pockets of extreme to exceptional drought were in place from Texas to Minnesota according to August 1 data in the U.S. Drought Monitor.
Website visitors can comment on “Eye on the Storm” posts (see comments policy below). Sign up to receive notices of new postings here.