High humidity makes a hot day feel oppressive because the human body is acutely sensitive to moisture in the air. Determining the most humid location requires focusing on the actual quantity of water vapor held in the atmosphere, rather than just the percentage. The most extreme humidity occurs when the air contains the maximum possible amount of moisture.
How Extreme Humidity is Measured
The most commonly reported metric, Relative Humidity (RH), can be misleading when assessing the world’s most humid places. RH expresses the amount of water vapor in the air as a percentage of the maximum amount the air can hold at a specific temperature. Since warm air holds significantly more moisture than cold air, 100% RH in a cool environment represents a much smaller volume of water than 100% RH in the tropics.
A more accurate measure of absolute moisture content is the Dew Point temperature. The dew point is the temperature to which air must be cooled for water vapor to condense into liquid water. A higher dew point directly indicates a greater concentration of water vapor, making it the definitive metric for identifying the most humid location.
Identifying the Most Humid Location
Based on the highest sustained dew point measurements, the coastal region bordering the Persian Gulf holds the record for the most extreme humidity. The port city of Dhahran, Saudi Arabia, recorded the world’s highest measured dew point temperature on July 8, 2003. The dew point reached 35°C (95°F), with the air temperature climbing to 42°C (108°F).
This extreme atmospheric moisture resulted in a calculated heat index that soared to 81.1°C (178°F). Other nearby Persian Gulf cities, such as Bandar Mahshahr in Iran, have also recorded exceptionally high dew points near 32°C (90°F). These intense conditions represent the highest absolute moisture content ever registered by weather stations.
The Unique Climatic Drivers
The unique geography and oceanography of the Persian Gulf create a perfect environment for generating and trapping this record-breaking moisture. The Gulf is a relatively shallow, semi-enclosed body of water, which allows its Sea Surface Temperatures (SSTs) to become exceptionally high during the summer months, reaching up to 37°C (98°F). This leads to a massive rate of water evaporation into the lower atmosphere.
The surrounding Arabian Peninsula is a vast desert, and the strong summer sun intensifies the heat over the land. This combination of intense surface heating and high evaporation produces an extremely moist and hot boundary layer of air just above the water.
A seasonal atmospheric pattern, often an anticyclone, contributes to low wind circulation over the region. This stagnant air mass acts like a lid, preventing the moist air from dispersing vertically or horizontally. When onshore winds push this highly saturated air mass from the Gulf over the coastal cities, the resulting dew points become trapped at dangerously high levels. The topography of the region, which is essentially a low basin surrounded by land, further contributes to the sustained moisture levels.
Humidity Versus Precipitation
It is important to distinguish between high humidity and high precipitation, as the most humid places are often not the wettest. The Persian Gulf coast, despite having the world’s highest absolute humidity measurements, is a desert region with minimal annual rainfall. Here, the air is saturated with water vapor, but atmospheric conditions do not favor the formation of clouds and rain.
By contrast, places like Mawsynram, India, are known as the wettest spots on Earth, receiving over 11,000 millimeters of rain annually. While Mawsynram experiences high relative humidity, the monsoonal conditions cause the moisture to be efficiently wrung out of the air as extreme rainfall, unlike the Persian Gulf where the moisture remains trapped in the air.