Warm, moist tropical air is needed for monsoon storms to get going over Southeast Arizona. That is why we track the dew point numbers very closely from June to September.
When dew points are below 50°, the air is generally too dry for widespread heavy downpours. When dew points are at or above 54° and conditions are favorable in the atmosphere for storm development, storms can form and produce heavy, flooding rains.
The Tucson National Weather Service records the dew point data throughout the monsoon. Data is put into the record books from June 15th through September 30th.
Dew points are the temperature at which the water vapor in the air condenses into liquid water. A high relative humidity indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature and that the air is completely saturated with water. When the moisture content remains constant and temperature increases, relative humidity decreases.
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