National Weather Service United States Department of Commerce

Lala Impacting Hawaii; Severe Thunderstorm and Flash Flooding Risks; Excessive Heat

Areas of gusty winds, heavy rain leading to flash flooding, and high surf continue across portions of Hawaii as Tropical Storm Lala continues to move away from the islands. Severe thunderstorm, heavy rainfall, and flash flooding threats continue from the Midwest to the Mid-Atlantic and across the central High Plains. Record heat continues for areas of the central/southern Plain into the Southeast Read More >

A Discussion on Water Vapor (Moisture)

QUESTION 1:

In the winter, if the air temperature was 40 F and the dewpoint was also 40, what would the relative humidity be? Now, in the spring, if the air temperature was 70 and the dewpoint was 70, what would the relative humidity be? In which situation would if feel more humid? What does this tell you about relative humidity?

ANSWER 1:

If the air temperature and dewpoint temperature were both 40, the relative humidity would be 100 percent. Likewise, if the air and dewpoint temperature were both 70, the relative humidity would again be 100 percent. Despite the relative humidity being the same in both cases, it certainly would feel more humid if the air and dewpoint temperatures were both 70 degrees. This shows how the relative humidity tells you little about the actual moisture content of the air (much more moisture is contained in the air for the summer case), and how the same relative humidity value can occur in completely different situations having very different "feels" to our bodies.

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