National Weather Service Weather Forecast Office

     Jacksonville, a very large metropolitan area covering 840 square miles, extends from the Atlantic Ocean to about 40 miles inland.  Downtown Jacksonville is located some 16 miles inland on the St. Johns River.  The surrounding terrain is level. Easterly winds blowing about 40 percent of the time produce a maritime influence that modifies to some extent the heat of summer and the cold of winter. Summers are long, warm, and relatively humid.  Winters, although punctuated with periodic invasions of cool to occasionally cold air from the north, are mild because of the southern latitude and the proximity to the warm Atlantic Ocean waters.  Because of the nearness to the ocean, climatic features across the city vary.  For example, during the summer months, temperatures at Jacksonville International Airport, located 17 miles inland, usually reach into the lower and mid 90's before being tempered by the sea breezes.  Temperatures along the beaches rarely exceed 90 degrees.  Summer thunderstorms usually occur before the noon hour along the beaches, while afternoon thunderstorms are the rule inland.
     The annual temperature for Jacksonville is between 68 and 69 degrees.  June, July, and August are the hottest months, with temperatures averaging near 80 degrees.  December, January, February are the coolest months, with temperatures near the middle 50's.  Temperatures exceed 95 degrees only about ten times a year.  Night temperatures in summer are usually comfortable, rarely failing to drop below 80 degrees.
     The greatest rainfall, mostly in the form of local thunderstorms, occurs during the summer months when a measurable amount can be expected one day in two.  Rainfall of 1 inch or more in 24 hours normally occurs about fourteen times a year, and very infrequently heavy rains, associated with tropical storms, reach amounts of several inches with durations of more than 24 hours.
     The atmosphere is moist, with an average relative humidity of about 75 percent, ranging from about 90 percent in early morning hours to about 55 percent in the afternoon.  Prevailing winds are northeasterly in the fall and winter months, and west-southwesterly in spring and summer.  Wind movement, which averages slightly less than 7 mph, is 2 to 3 mph higher in the early afternoon than the early morning hours, and slightly higher in spring than in other seasons of the year. Although this area is in the Hurricane Belt, this section of the coast has been very fortunate in escaping hurricane-force winds. Most hurricanes reaching this latitude have tended to move parallel to the coastline, keeping well out to sea. Others have lost much of their force moving over land before reaching this area.