The United States is a large country with diverse climates and temperatures across its 50 states. Some states experience sweltering hot summers while others see more moderate temperatures year-round. Determining the hottest state depends on how we define “hottest.” This article will examine multiple metrics like average summer highs, record high temperatures, and average annual temperatures to provide a comprehensive look at which U.S. state could be considered the hottest.
Average Summer High Temperatures
One way to evaluate the hottest state is to look at average daily high temperatures during the summer months of June, July, and August. States in the Southwest region of the U.S. tend to experience the highest summer temperatures.
According to climate data from the National Oceanic and Atmospheric Administration (NOAA), the state with the highest average summer high temperature is Arizona. Here are the average summer highs for Arizona and other hot states:
| State | Average Summer High Temperature (°F) |
|---|---|
| Arizona | 107.0°F |
| Nevada | 103.7°F |
| Texas | 98.3°F |
| Oklahoma | 97.8°F |
| New Mexico | 96.0°F |
| California | 95.7°F |
| Louisiana | 95.0°F |
As you can see, Arizona takes the top spot with an average summer high of 107°F – several degrees hotter than second place Nevada at 103.7°F. Texas, Oklahoma, New Mexico, California, and Louisiana all have average summer highs in the 95-98°F range.
The Southwest’s Hot and Dry Climate
What makes the Southwest states like Arizona so hot in summer? The region experiences a very hot and dry climate type known as desert or arid. High pressure systems dominate in the summer leading to cloudless skies, intense sun exposure, and daytime heating. The lack of moisture in the air allows heat to build up through the day without relief. Mountain ranges like the Sierra Nevada in California or the Rockies in Arizona/New Mexico also create a rain shadow effect that keeps the interior Southwest extra dry and hot.
Coastal States Are Milder
In contrast, coastal states in other regions have more moderate summertime temperatures. Eastern and Western coastal states all maintain cooler summer highs in the 80s and 90s°F thanks to onshore winds and airflow from the ocean. The sea breeze effect keeps these coasts cooler than the interior desert states in summer. So while the Southwest baking under sunny skies, Gulf Coast or Pacific Coast states enjoy marginally cooler summer days.
Record Hot Temperatures
Another way to look at the hottest states is to examine record high temperatures. Even though Southwest states see the highest summer averages, the hottest temperature ever recorded in the U.S. was 134°F in Death Valley, California on July 10, 1913. Here are the top 5 hottest temperatures measured:
| Location | Hottest Temperature | Date |
|---|---|---|
| Death Valley, CA | 134°F | July 10, 1913 |
| Greenland Ranch, AZ | 128°F | June 29, 1994 |
| Ozona, TX | 120°F | June 5, 1994 |
| Basin, WY | 119°F | July 12, 1900 |
| El Azizia, Libya | 136°F | Sept. 13, 1922 |
Based on record alone, California stands out for having the hottest temperature not just in the U.S. but globally. However, many weather historians debate the accuracy of the 1913 Death Valley reading. El Azizia, Libya claimed the world record for over 90 years with a 136°F reading, but it too was found to be faulty. Many modern meteorologists believe temperatures of 134-136°F are not possible on Earth. Still, Death Valley and the Southwest U.S. more broadly certainly see extreme hot temperatures.
Factors Producing Record Heat
Why do these locations reach such high extremes? Many of the same reasons the Southwest states see the highest summer averages – sunny skies, lack of moisture, downslope heating, and a hot arid climate. The specific weather conditions on record temperature days also play a role. Key factors helping produce record heat include:
- Powerful high pressure systems leading to sinking, dry air and cloudless skies
- Downslope, compressional heating as air flows over mountains and descends into valleys and basins
- Hot mid-level air aloft heating the ground further as it mixes down
- Ground surfaces like bare rock, sand or pavement rapidly heating air near the surface
- Dry air allowing excessive heating without evaporative cooling effects
- Light wind conditions preventing mixing and cooling from convection
All these ingredients came together in Death Valley in 1913 to produce the highest air temperature ever recorded. However, some still doubt the accuracy given inconsistencies in the reading.
Average Yearly Temperatures
Examining average annual temperatures is another way to look at the hottest states. While Southwest states experience the most intense heat in the summer, the year-round climate tells a slightly different story in some parts of the country.
Florida narrowly beats out Hawaii for the highest average annual temperature across all U.S. states. Here are the top 5 states by yearly average:
| State | Average Annual Temperature |
|---|---|
| Florida | 70.7°F |
| Hawaii | 70.0°F |
| Louisiana | 66.4°F |
| Texas | 64.2°F |
| Arizona | 63.4°F |
Coastal southern states dominate the highest average yearly temperatures, with Florida barely edging out tropical Hawaii. Louisiana, Texas and Arizona fill out the top 5, with their southern latitudes and Gulf/Southwest climates keeping them warmer through the year.
Moderate vs Extreme Temperatures
Compared to summer highs, the yearly average paints a somewhat different picture of the hottest states. Arizona, Nevada and inland California see the most extreme high temperatures in summer. But the overnight lows and comfortable winters in these deserts bring down the annual mean temperature compared to southern coastal climates. Places like Florida and Hawaii experience less variable, more moderate temperatures year-round without cold winter extremes. This moderation balances out to a higher annual mean despite hotter individual summer days in the desert.
Humidity Makes the Heat Feel Worse
When discussing hot weather, it’s important to consider humidity as well as air temperature. The heat index accounts for humidity to determine how hot the air actually feels to your body.
High humidity makes conditions feel hotter by limiting the evaporation of sweat from your skin. Since sweat doesn’t evaporate as well, it becomes harder for your body to shed heat. You feel hotter as a result. Dry heat conditions allow more evaporative cooling from sweat, meaning 100°F with 30% humidity feels much more bearable than 90°F with 70% humidity.
States in the Southeast and Gulf Coast regions experience higher humidity on average than the dry Southwest. Florida and Louisiana have high annual humidity alongside hot temperatures. Here are the 5 most humid states based on average relative humidity:
| State | Average Relative Humidity |
|---|---|
| Florida | 74% |
| Louisiana | 74% |
| Mississippi | 74% |
| Alabama | 72% |
| Georgia | 71% |
Combining heat and humidity, these Southeast states feel the most sweltering in summer. The Southwest may reach higher air temperatures, but the low desert humidity provides some heat relief. Coastal heat still feels oppressive due to moisture off the Gulf of Mexico and Atlantic Ocean.
Heat Index Tables
Weather forecasters use heat index tables to account for humidity and determine how hot it actually feels outside. Here is an example heat index table showing degrees Fahrenheit:
| 40% Humidity | 50% Humidity | 60% Humidity | 70% Humidity | 80% Humidity | 90% Humidity | |
|---|---|---|---|---|---|---|
| 90°F | 86°F | 88°F | 91°F | 95°F | 100°F | 107°F |
| 100°F | 96°F | 101°F | 105°F | 113°F | 123°F | 135°F |
| 110°F | 106°F | 114°F | 123°F | 134°F | 148°F | 162°F |
At 100°F with 80% humidity, it feels like 123°F to your body! The Southwest may reach 120°F at 10% humidity, but along the Gulf Coast 100°F at 80% humidity would be brutal.
Global Warming Impacts
As average temperatures increase due to global warming, heat waves are becoming more intense and dangerous. The hottest states will face worsening summer heat.
The EPA reports extreme heat waves in recent years, such as:
- July 2022: Excessive heat dome with over 100°F temperatures gripping the Central and Eastern U.S. for weeks
- June 2021: Pacific Northwest/British Columbia heat wave with record temperatures up to 121°F leading to hundreds of deaths
- July 2020: Heat wave with 120°F Death Valley temperatures and 130°F ground surface temperatures
Global warming has increased the likelihood of record-breaking, deadly heat events. If greenhouse gas emissions continue rising, these events will become more frequent and intense in the coming decades.
Researchers project that by 2100, the number of days per year above 100°F will quadruple in the Southwest, triple in the Southeast, and double in the Northeast. The hottest states like Arizona, Texas and Florida will see 100°F+ days nearly every summer day.
Rising sea levels may also increase coastal humidity as warmer oceans evaporate more moisture into the air. This combination of extreme heat and humidity could push dangerous heat indexes above the human survivability threshold across wide regions.
Public Health Risks
Thehottest states already face public health risks from heat that will get worse. Hazards include:
- Heat exhaustion when body temperatures rise to 100-104°F
- Heat stroke when core temperature exceeds 104°F, causing organ damage or failure
- Dehydration from excessive sweating
- Exacerbated respiratory and cardiovascular disease
- Kidney stones and other issues from dehydration
Vulnerable populations like children, seniors and outdoor workers are most at risk. But extreme heat can affect anyone by overwhelming the body’s ability to thermoregulate and stay cool.
Public health preparation and infrastructure upgrades will be crucial in the hottest states. Air conditioning, cooling centers, early warning systems, urban green spaces, and ready access to fluids will help reduce risks.
Conclusion
Determining America’s hottest state depends on the metrics used. Arizona takes the crown for highest average summer highs, while Florida sees the hottest year-round mean temperature. The Southwest faces more extreme heat thanks to its dry desert climate, but humidity makes the Southeast feel most oppressive during heat waves. Looking ahead, global warming will exacerbate summer heat, especially in already hot southern states.
Preparing infrastructure and public health systems for worsening extreme heat will be essential in the coming decades. But reducing greenhouse gas emissions remains critical to avoid truly dangerous levels of warming. The country’s hottest states make clear that summer heat is nothing to take lightly as climate change progresses.
