May Weather in San Diego County

From the National Weather Service:

May is normally characterized by persistent overcast skies during the night and morning hours and by less sunshine than any other month, except June.

Temperatures continue their upward trend with the most noticeable rise in nighttime readings. The normal daily maximum for the month is 68.5 degrees, the normal daily minimum 59.4 degrees and the mean 64.0 degrees. On 10 days the record maximum temperatures are in the 90s and was 98 degrees on May 25, 1896, the absolute high for May.

However, the cool sea breeze prevails nearly every day and temperatures above 80 degrees rarely have been reached. Nights are uniformly mild and the lowest reading during the month was 45 degrees in 1915.

Our long dry season usually begins in May and the average number of days with measurable rain is 2 with an average monthly total of 0.12 inch. However, on three occasions the monthly total has exceeded 2 inches with the greatest rainfall 2.54 inches in 1921.

Stormy weather is almost unknown during the month and winds over 20 mph have been infrequent. Only twice have winds over 30 mph been recorded at the National Weather Service office. The highest wind ever recorded in May was 40 mph on May 29, 1988. The other time winds over 30 mph were recorded was in 1922 when winds of 37 mph were registered.

Although skies are commonly overcast during the night and morning hours, heavy fog is rare, the average being only once each May.

Clear days number eight, partly cloudy 12 and cloudy 11. Possible sunshine is 58 percent on any given day, about 11 percent less than the winter days’ average. May and June are the cloudiest months of the year, which is a paradox because they are two of the five driest months of the year. Relative humidity shows little change from April with humidity in the early morning 77 percent, near noon 65 percent and in the afternoon 64 percent.