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Because of its position in the northeastern part of the state, near the Atlantic Ocean and the St. Johns River, Jacksonville, Florida, has a climate that is characterised by long, hot and humid summers, mild winters, frequent summer rainfall and a lot of sunshine. The city has, over the years, come across some remarkable temperature extremes, so the local weather should be checked before going outside on a day.
The geographical position of Jacksonville accounts for a great deal of this pattern. The city is situated in Duval County in northeastern Florida and lies at about 30° north latitude. To the east is the Atlantic Ocean, and the St. Johns River passes through the Jacksonville area before flowing into the ocean. The city is quite low in elevation, the official weather station of Jacksonville International Airport being only a few metres above sea level.
The fact that Jacksonville is situated by the coast means that it has a humid subtropical climate; the influence of the ocean causes the temperatures to be less extreme than they would be at places further inland, and the warm, moist air leads to hot summers and a frequent occurrence of thunderstorms.
The long-term climate record for Jacksonville indicates that the city is warm for a large part of each year, and the NOAA and the National Weather Service use the 1991–2020 climate normals as their standard reference period for current averages.
At Jacksonville International Airport the daytime temperatures usually go from the mid-60s°F in January to about 92°F in July. August is similarly hot before the temperatures start to decrease in September and October. Although January is typically the coldest month, winter days can still be warm enough for outdoor activities.
Another characteristic of Jacksonville's weather is rainfall. The city has an annual average of about 53.4 inches of precipitation according to the 1991–2020 normals. The months from June to September are especially wet, each of them usually getting about 6 to 8 inches of rain.
Summer rain is usually caused by thunderstorms that occur in the afternoon. It's possible for a morning to start off with sunny weather and high humidity before clouds form later in the day. Both residents and visitors can benefit greatly by looking at the forecast before going to the beach, the park or other outdoor locations.
Jacksonville starts to become noticeably warmer in the spring, with March and April seeing temperatures rise and more sunshine, and by May it is already similar to summer.
By June the effects of the heat, humidity and rainfall are much more apparent. July and August are usually the hottest months, the average high temperature being about 91–92°F. The warm nights are likewise a significant feature of the local climate, average minimum temperatures staying above 70°F throughout the summer.
In September the temperature can still be very warm even though the rainfall remains high; in October the temperatures are generally more comfortable and by November there is a clearer shift towards the mild winter conditions.
Winter is much milder than in most of the United States, with daytime highs in January usually being in the mid-60s°F, though at times cold fronts can cause much colder weather. The historical record for Jacksonville also shows some extreme temperatures. Since 1871 the National Weather Service has maintained a long climate record, which includes more than 150 years of observations for comparison.
The UV Index in Jacksonville, Florida is also a significant element of the local weather. Since the city is fairly far south and gets a lot of sunshine, ultraviolet exposure can become considerable long before the hottest period of summer.
Historical data on UV levels exhibits a clear seasonal pattern, with maximum UV Index values reaching about 4 in January, increasing to approximately 8 in March, rising to around 10 in April and May, and reaching 11 in June and July, a figure that falls within the Extreme category, and staying high at about 9 in September before the UV levels decrease gradually in the autumn.
Long-term records of UV radiation also demonstrate just how intense exposure can be; historical data for Jacksonville from 1994 shows that July is the month with the highest average UV Index, about 11.7, and a maximum UV Index of 12.77 was recorded on May 3, 2010.
It is important to keep this in mind since temperature and UV radiation are not the same. Even a pleasant spring afternoon can have a high UV Index, and the presence of clouds or cooler temperatures doesn't mean that UV exposure can be ignored.
If the UV Index is in the high or very high range, staying in direct sunlight for a long time may increase the chance of sun damage. While the strongest part of the day is going on, basic protection like sunscreen, sunglasses, a hat and shade can make outdoor activities not only safer but also more comfortable.
In Jacksonville in particular outdoor activities are closely linked to the local environment since beaches, parks, waterways and trails may all be appealing in the warmer months but the intense sunshine and high humidity can make the conditions more demanding than they at first seem.
Looking at the Jacksonville weather forecast and UV Index together gives a better understanding of how the day will actually feel. The temperature informs you about the heat, rainfall shows the probability of wet weather, and the UV Index gives details about ultraviolet exposure.
When one looks back at Jacksonville's climate history it becomes clear that the city has a remarkably steady warm-weather pattern: hot summers, mild winters, a good deal of rainfall and intense seasonal UV exposure.
Different years can still be quite varied; one summer might see more thunderstorms whereas another could experience longer spells of heat. The temperature during winter can also vary considerably according to the number and intensity of the cold fronts that affect northern Florida.
For anybody who lives in Jacksonville or one who visits the city, the historical climate averages can be of some use when one wants to get a broad understanding, but it is still the daily forecast that gives the best indication of the present conditions.
The place where Jacksonville is situated, together with its proximity to the Atlantic and the fact that it is low in elevation, means that the city has a special kind of weather; with the high UV Index during summer and a lot of sunshine, it is now obvious that it is useful to check both the Jacksonville, Florida weather conditions and the UV Index when planning on spending time outside.