Record-Breaking Heatwaves: Arizona, Florida, and Maine Experience Hottest Month in History

2023-08-14 07:00:00

From Arizona to Florida, and even Maine, many states, cities and towns had their hottest month since climate records began.

July 2023, already recognized as the hottest month in Earth’s recorded history, featured brutal heat waves that scorched the southern and coastal states of America, several of which experienced their hottest month on record, while the The Upper Midwest and Northern Plains were surprisingly mild.

For the contiguous United States as a whole, July ranked as the 11th-warmest summer in records going back to 1895, according to NOAA’s national monthly climate report.

It was the warmest 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 records for each of these states, as shown in the monthly averages below. The magnitude of the heat record was especially shocking in Arizona and New Mexico.

Arizona: 85.7 degrees Fahrenheit (previous record 84.1°F, August 2020) Florida: 84.1°F (previous record 84.0°F, July 2016) New Mexico: 78.6°F (previous record 76.9°F, July 2016) Maine : 70.1°F (previous record 70.0°F, July 1921 and July 1952)

Fifteen additional states along an arc, from Washington to California, via Texas, Maryland, and New Hampshire, had their top ten warmest Joules (see Figure 1 below). Most of the nation was at least slightly warmer than average, while being among the coolest thirds of the joules on record in Iowa, Minnesota, Nebraska, and North and South Dakota, as persistent low pressure at upper levels it sent a series of cold fronts through the area, keeping temperatures relatively mild. Figure 1. Average temperature rankings for each contiguous US state for July 2023 compared to 129 years of records dating back to 1895. Darker orange colors indicate warmer conditions; darker blue denotes cooler conditions. (Image credit: NOAA/NCEI)

All-time record heat stretches from southern California to southern Florida

All-time record heat in July affected not only much of the Sun Belt, but also several places further to the northwest and northeast, encircling a “ring of fire” that spanned the southern states of the United States.

Here’s a probably incomplete list of cities that broke or tied their records in July for the warmest month on record, in many cases exceeding more than a thousand months through more than a century of climate history. The starting year of the official climate files for each city is labeled as POR (registration period).

Several 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, which span over 40 degrees Fahrenheit, is as startling as their geographic spread.

Quillayute, WA: 63.1°F (tied with Aug 2013; POR 1966-) Palm Springs, CA: 98.5°F (previous record 97.6°F in Jul 2021; POR 1922-) Las Vegas, NV: 97.3°F ( previous record 96.2°F in Jul 2010; POR 1937-) Needles, CA: 101.8°F (previous record 100.9°F in Jul 2006; POR 1888-) Kingman, AZ: 88.5°F (previous record 87.6°F in Aug 2020; POR 1901-) Phoenix, AZ: 102.7°F (previous record 99.1°F in Aug 2020; POR 1895-) Albuquerque, NM: 85.6°F (previous record 83.8°F in Jul 2003; POR 1892 -) Roswell, NM: 88.1°F (previous record 87.6°F in Jul 2020; POR 1893-) Eagle Nest, NM: 64.7°F (previous record 63.4°F in Jul 2011; POR 1929-) Las Vegas, NM: 73.8°F (previous record 72.7°F in Jul 2011; POR 1940-) Socorro, NM: 85.0°F (previous record 82.9°F in Jul 1951; POR 1893-) El Paso, TX: 91.6°F (previous record 88.9°F in June 1994 and July 2020; POR 1887-) Baton Rouge, LA: 87.8°F (previous 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 (previous record 85.9°F in June 1981; POR 1892-) Tampa, FL: 86.5°F (previous record 86.3°F in June 2022; POR 1890-) Sarasota -Bradenton, FL: 86.2°F (previous record 85.8°F in Jul 2020; POR 1911-) Lakeland, FL: 85.5°F (previous record 85.1°F in Aug 1987 and Jul 2016; POR 1948-) Peak Gorda, FL: 85.8°F (previous 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 (previous record previous record 85.9°F in Jul 2020; POR 1895-) Dry Tortugas, FL: 88.7°F (previous record 87.4°F in Aug 2011; POR 1950-) Key West, FL: 87.7°F (previous record 87.5°F in Aug 2007; POR 1872-) Marathon, FL: 89.5°F (previous high 88.0°F in Jun 2019; POR 1950-) Caribou, ME: 71.5°F (previous high 70.9°F in Jul 2018; POR 1939-) Dover-Foxcroft, ME: 71.4°F (previous record 70.5°F in July 2018; BY 1973-)

The star of this misery list is Phoenix, where the monthly average of 102.7°F (39.3°C) broke the previous record for any month by a staggering 3.6°F (2.0°C). No major city in the United States had ever seen a monthly average exceed 100°F before; the warmest previous month on record for any city in the United States was 102.2 °F in July 1996 in Lake Havasu City, Arizona, according to climatologist Brian Brettschneider.

All but one day (July 31) hit at least 110°F (43.3°C) in Phoenix; Along with June 30, the city endured a record 31-day streak with highs of at least 110°F, and also experienced a record 16-day streak in which temperatures never dropped below 90°F.

As of July 29, 39 heat-related deaths have been recorded in Phoenix’s Maricopa County, with another 312 deaths under investigation. Equally alarmingly, heat mortality records compiled by the Centers for Disease Control and Prevention show that the average number of heat-related deaths in the United States over a five-year period has nearly doubled since 2010,

And that doesn’t include this year. (See our detailed 2020 post on how heat deaths are assessed.)

Along with the monthly records mentioned above, at least two US weather stations with a long recording period set all-time daily records in July:

Kingman, Arizona, 114 °F (45.6 °C) on July 15 (previous record 113 °F on July 20, 2017; POR 1901-) Las Vegas, New Mexico, 100 °F (37.8 °C) on July 18 July (previous record 99 °F on various dates; BY 1940-)

Death Valley, California had the hottest temperature on record on the planet so far in 2023: 53.9 °C (129.0 °F) at Saratoga Spring on July 16. This is just below the reliably measured world temperature record of 130 °F (54.4 °C), set on July 9, 2021. (A reading of 134 °F in Death Valley on July 10, 1913, which currently listed as the world record for the highest temperature, it has been disputed and dismissed 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 ( 40°C).

Puerto Rico y Alaska

The record temperatures were not only recorded in the contiguous United States. San Juan, Puerto Rico had its fifth warmest July in 125 years of records, averaging 84.6 °F, after its warmest June on record (also 84.6 °F). In Utqiagvik, Alaska, July was the hottest month in 105 years of data, with an average temperature of 48.4 °F (previous record 48.3 °F in July 2019)

How did the Southwest and South Florida get so hot?

As natural weather variations unfold, we can expect some days, months, and years to exceed the long-term trend, which explains why heat waves tend to get even hotter when they occur in a warming climate.

The subtropical belt that encircles the planet at latitudes 25 to 30 degrees north is known for subsiding 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 to around 19,000 feet) to record highs across the southern United States. In fact, the 500 millibar surface was at record heights over most of the world’s tropical areas, as well as many parts of the subtropics.

500 mb height rankings for July 2023 compared to all Julys since 1940. Dark red indicated record heights. Seems bad. ???????? pic.twitter.com/5GB0IuQEep— Brian Brettschneider (@Climatologist49) August 6, 2023

The obvious place to start in looking at the searing July heat in the American South (and many other parts of the world, as we’ll detail in a post next week) is long-term warming caused by the use of fossil fuels, which is now about 2 degrees Fahrenheit (1.2 °C) above pre-industrial values globally. The World Weather Attribution Program concluded in a July 25 report that “maximum heat as of 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 a heat wave like this 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 Climate Change Index, Climate Central found that “July heat levels in the southern United States, Mexico, Central America, and the Caribbean would have been extremely unlikely without human-caused climate change.” In many of the cities mentioned above that set record monthly highs, the level of heat on certain days was four to five times more likely due to human-induced climate change, according to Climate Central.

In larger cities, including Phoenix, urban heat island is another factor exacerbating heat waves (and a heat island is a type of human-induced climate change itself). However, a number of smaller cities and towns also set all-time records for July, as evidenced by the list above, so heat islands weren’t the only culprit. As he pointed According to the National Weather Service Office in San Diego, temperatures within a few miles above Earth’s surface, as inferred by measurements from weather balloons and satellites, were also at record levels in July. Additionally, the aforementioned all-time highs were set at elevations above sea level, which ranged from 3 feet in Marathon, Florida, to 8,238 feet in Eagle Nest, New Mexico. Neither of these locations would qualify as an urban heat island in any sense.

Another factor at 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 weak this year, allowing the landscape to heat up much more easily.

Throughout southern and western Florida, both the atmosphere and the adjacent ocean were operating at near-record levels of heat in July. Many buoys just offshore reported sea surface temperatures above 95°F, and in Manatee Bay, the ocean surface reached an astonishing 101.1°F (38.4°C). Unusually light trade winds helped limit mixing just below the sea surface, allowing the paper-thin surface to warm even more than usual, as Jeff Masters noted in a series of tweets. The organic-rich outflow from the Everglades may also have increased nearshore water temperatures by darkening the sea surface and therefore absorbing more sunlight, she added.

The 101.1°F water temperature in South Florida’s Manatee Bay could be the second-highest in world history, behind the 102°F recorded there in August 2017, a month with exceptional heat in the Florida waters. A few weeks later, Category 4 Hurricane Irma fed off the warm waters; 97 people died and damage exceeded $60 billion.

The heat in South Florida was also likely intensified in July by the lack of intrusions of sunlight-reflecting dust from the Sahara. And regional and global warmth in July may have received modest boosts from two other ongoing influences we mentioned in a July post: a decline in sun-blocking sulfur dioxide pollution from global shipping since 2020 and the undersea eruption in January 2022 from the Hunga Tonga-Hunga Ha’apai volcano, which increased the presence of water vapor (a greenhouse gas) in the stratosphere by up to 15 percent.

Hail again battered the nation during a record month of severe weather. Even after a June marked by hailstorms after hail stormsJuly was an exceptional month in terms of severe weather, according to the Capital Weather Gang from the Washington Post. The severe weather was fueled in part by a jet stream that remained stronger than usual for midsummer for much of the month. The jet stream has been squeezed between a cold upper level low pressure in the Midwest and a warm upper level high pressure in the Southern Plains.

The NOAA/NWS Storm Prediction Center record 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 of at least 58 mph. That’s higher than the final count for any month in data going back to 2004. For June and July combined, the 532 reports of very large hailstones (2 inches or more in diameter) have already broken the record for 378 that was established in 2009 for the entire meteorological summer (from June to August), and there is still a month to go.

As of August 9, NOAA had cataloged 15 separate weather disasters in the United States that exceeded one billion dollars, which is a record for this time of the year even after adjusting for inflation. Thirteen of these disasters were due to severe weather.

We are reaching the inevitable point where insured losses from thunderstorms in the United States in 2023 will exceed $40 billion for the third time in history (2011 and 2020).

Losses currently average more than $1 billion per outbreak; being the second higher figure only after 2011. Upper-level recurring lows in the Midwest helped nine states have a July in the top 10 wettest (see Figure 2 below), including Michigan, New York, Oklahoma, Pennsylvania, and all of the states of New England except Maine. For the continental United States as a whole, it was the 45th driest July in 129 years of record. Figure 2. Average precipitation ranking for each contiguous United States during July 2023 compared to 129 years of records going back to 1895. Darker green colors indicate wetter conditions; darker brown color denotes drier conditions. (Image credit: NOAA/NCEI)

The drought was less widespread than it had been in the past several Julys, especially after a wet winter in the western United States. However, areas of extreme drought occurred from Texas to Minnesota, according to data from the August 1st in the United States Drought Monitor.