25 Most Humid U.S. Cities Ranked: Is Your Town On the List?
Humidity and problems such as mold growth go hand in hand. Does that mean the most humid cities in the United States are also the worst cities for mold allergies? Let’s look at the data about the worst cities for humidity and mold.
What Does High Humidity Mean?
Relative humidity measures the moisture in the air as a percentage of its total holding capacity. A 50 percent humidity measurement means the moisture in the air is half of its maximum capacity.
Humidity can make a hot day feel even hotter, and this effect can be explained by the science of how the body reacts with the environment. Sweating is the body’s natural air conditioner, and as moisture evaporates from the skin, the body cools down.
However, if a city reaches the upper limits of 100 percent relative humidity, the air is saturated and cannot hold any more water. This means perspiration stays on the skin rather than evaporating into the air. This result is that the higher the humidity, the less the body can cool itself through sweat evaporation.
What’s a Good Humidity Level?
Relative humidity between 30 and 50 percent is typically the most comfortable range for people. Interestingly, buildings have similar preferences. The EPA recommends that indoor humidity levels be kept between 30 and 50 percent to stop the growth of mold and discourage pests such as cockroaches and dust mites.
Additionally, humidity levels ranging from 55-60% and above can contribute to problems like mold growth and wood rot.
Mold can contribute to unhealthy conditions and affect structural integrity, and wood rot can significantly impact the stability of your underlying structures. Rotting wood supports like floor joists in crawl spaces can lead to sagging and uneven floors, and fail to properly support the floors above.
When you get in touch with your local Groundworks experts, we will test the air and the moisture of the wood during our inspections so you know what you’re dealing with in your crawl space.
Because ground moisture typically leads to indoor humidity problems, the most effective home dehumidification is usually in the basement or crawl space. By properly sealing and dehumidifying these lower levels, the effects can be felt throughout the house because of the air’s natural upward circulation.
Which Cities Have the Highest Humidity?
Using Comparative Climatic Data compiled in 2023 from the National Oceanic and Atmospheric Administration (NOAA), we identify the cities with the highest average annual relative humidity, based on morning and afternoon humidity measurements.
25 Most Humid Cities in the United States
| Rank Number and Location | Average Annual Humidity Percentage |
|---|---|
|
1. St. Paul Island, AK
|
86%
|
|
2. Cold Bay, AK
|
84%
|
|
3. Quillayutte, WA
|
82%
|
|
4. Yakutat, AK
|
82%
|
|
5. Barrow, AK
|
81%
|
|
6. Astoria, OR
|
80%
|
|
7. Juneau, AK
|
79%
|
|
8. Bethel, AK
|
79%
|
|
9. San Francisco, CA
|
78%
|
|
10. Kotzebue, AK
|
78%
|
|
11. Annette, AK
|
78%
|
|
12. Port Arthur, TX
|
77%
|
|
13. Olympia, WA
|
76%
|
|
14. Lake Charles, LA
|
76%
|
|
15. Galveston, TX
|
76%
|
|
16. Nome, AK
|
76%
|
|
17. Kodiak, AK
|
76%
|
|
18. Corpus Christi, TX
|
75%
|
|
19. King Salmon, AK
|
75%
|
|
20. Brownsville, TX
|
75%
|
|
21. Sault Ste. Marie, MI
|
75%
|
|
22. New Orleans, LA
|
75%
|
|
23. Homer, AK
|
75%
|
|
24. Victoria, TX
|
75%
|
|
25. Valdez, AK
|
74%
|
We tend to associate humidity with cities in southern states such as Florida and Louisiana. Large bodies of water tend to cause more humidity because evaporation adds water to the air. Plus, warmer water evaporates more quickly, and so warmer cities near water are more apt to have high levels of humidity.
Interestingly, you’ll notice half of the cities listed here are located in Alaska.
Many Alaskan cities have high average relative humidity because cold air holds very little moisture, so even a small amount of water vapor can saturate it and result in high relative humidity. Coastal locations also receive constant moisture from nearby oceans, contributing to persistent fog, clouds, and dampness. However, despite the high relative humidity, Alaska’s absolute humidity (dew point) remains very low, meaning the air contains far less actual water vapor than warm, tropical places.
What Cities Have the Most Mold?
Mold is naturally found everywhere, but it grows most prolifically in damp areas with high humidity. In part, this means the cities with the highest humidity could also have high levels of mold. However, that’s only part of the story.
To measure mold, we first need to divide potential environments into indoors and outdoors. Even though the mold spores themselves may not be different, mold needs specific conditions to grow, and differences can occur between the environments.
For example, in a cold, wintry city, there are likely to be minimal outdoor mold spores. However, if a house in that setting has high humidity in the basement or crawl space, the warm, damp environment can create the ideal conditions for indoor mold growth.
When it comes to outdoor mold in the U.S., the growth of airborne mold spores is typically related to regional climate. Areas with high humidity, heavy precipitation, and low winds could see the worst problems. The peak is usually around July for the warmer states. For the cooler states, mold spores peak around October as piles of damp leaves and debris accumulate.
How Is Indoor Mold Growth Different?
Indoor mold can be especially damaging to one’s health and property. Mold allergy sufferers may even be prone to asthma attacks because of the duration of mold exposure.
Researchers have found that when it comes to indoor mold, “It is primarily the homes’ internal and external structural integrity that controls moisture and mold growth,” said one analysis by researchers at the Environmental Protection Agency (EPA) and the Department of Housing and Urban Development (HUD).
The EPA and the NY Academy of Medicine sampled air quality in homes across the country. They found indoor moldy conditions have less to do with geography than a home’s water problems or moisture conditions.
The research compared different home conditions based on the level of mold. Using the Environmental Relative Moldiness Index (ERMI), a home in the lowest quartile for mold had 24 percent of respondents say they had water damage, and 11 percent say they have a musty smell. In contrast, homes in the highest quartile of mold had 34 percent of respondents with water problems, and 24 percent said they have a musty smell.
Ready to Fix High Indoor Humidity? Trust Groundworks!
Controlling moisture damage, including mold, starts with managing indoor humidity. However, every home is different, with its own unique challenges and repair needs. Our team at Groundworks understands that. We’ll help you determine if the best solution is to improve drainage, add a vapor barrier, install a sump pump, or add a dehumidifier to your basement or crawl space. Contact us today for a free inspection and estimate.
High Humidity FAQs
Use a hygrometer, a device that measures humidity, to determine the moisture level in your basement.
It’s best to keep relative humidity below 60%, with ideal ranges falling between 30-50%.
The size of the dehumidifier you need depends on the size of the area you want to dehumidify and the level of humidity. Dehumidifiers are rated by the amount of moisture they can remove in a day, so larger spaces and higher humidity levels typically require a dehumidifier with a higher capacity. Groundworks experts are able to calculate the right unit for your home.
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