The atmosphere always contains moisture, which influences weather patterns and human comfort. Meteorologists use the dew point temperature as the most direct and consistent measure of humidity. Unlike relative humidity, which changes with air temperature fluctuations, the dew point provides an absolute value of the actual water vapor content in the air. This reading indicates how muggy the air feels.
Defining Dew Point
The dew point is the temperature to which air must be cooled, at a constant pressure, to become saturated with water vapor. When air reaches this temperature, the water vapor condenses into liquid droplets, forming dew, fog, or clouds. This condensation point occurs when the relative humidity reaches 100%.
Because it represents the actual quantity of moisture in the air, the dew point is a reliable gauge of human comfort. A dew point below 55°F (13°C) is considered dry and comfortable. As the dew point climbs into the 55°F to 65°F (13°C to 18°C) range, the air begins to feel sticky or muggy.
Once the reading exceeds 65°F (18°C), the atmosphere becomes oppressive, feeling heavy and tropical. This high measurement signifies a massive amount of water vapor available, often focusing attention on extreme weather events.
The World Record Dew Point
The highest officially recorded dew point temperature reached 35°C (95°F). This measurement was taken at 3 p.m. on July 8, 2003, in Dhahran, Saudi Arabia. The air temperature at the time was 42°C (108°F), indicating the air was extremely close to saturation.
The combination of the high air temperature and the record dew point resulted in a calculated heat index, or “feels like” temperature, of 81.1°C (178°F). This reading is considered the highest reliable, accepted measurement for a dew point, despite potential unconfirmed spikes elsewhere.
The Atmospheric Conditions Enabling Extremes
The Persian Gulf is uniquely suited to generate such extreme humidity. As a shallow, semi-enclosed body of water, its surface temperatures soar during the summer months, sometimes reaching 98°F. This creates a massive, continuous source of water vapor through evaporation.
The coastal geography of Dhahran is also a contributing factor. Air heavily laden with moisture from the warm sea is carried inland by light, steady onshore winds. A high-pressure system or a layer of warm air aloft often acts like a lid, trapping the moist air close to the surface and preventing mixing with drier air masses. This atmospheric trapping, combined with the super-heated moisture source, concentrates the absolute humidity to record levels.
Impact on Comfort and Health
Extremely high dew points pose a significant threat to human health by undermining the body’s primary cooling mechanism. Humans cool down when sweat evaporates from the skin. However, evaporation slows dramatically when the air is saturated with moisture, which is indicated by a high dew point.
When the dew point rises above the mid-70s F (mid-20s C), the body cannot effectively shed heat, and the core temperature begins to rise. This physiological strain forces the heart to work harder to dissipate heat. This inability to cool quickly leads to the risk of heat-related illnesses, such as heat exhaustion or heat stroke, causing the heat index to soar to dangerous levels.