Amelia Island water temperature, month by month
Key facts
The Atlantic here runs 57.9°F in January to 84.6°F in August, and holds 77.7°F or better from May to October. The sea lags the air by about two months in both directions.
The Atlantic off Amelia Island averages 57.9°F in January and 84.6°F in August — an annual swing of 26.7°F, which is much larger than most people expect from Florida. This is the north-east corner of the state, not the Keys.
The practical answer: the water holds 77.7°F or better from May through October. Outside that window it is swimmable for the determined and cold for everyone else.
- Average daily high to low
- Ocean temperature
Monthly mean sea temperature
| Month | Avg high | Avg low | Ocean | Feels |
|---|---|---|---|---|
| January | 64.3°F | 45.4°F | 57.9°F | Cold |
| February | 66.6°F | 48.6°F | 60.3°F | Cold |
| March | 72.2°F | 54.1°F | 64.7°F | Brisk |
| April | 77.4°F | 59.8°F | 71.2°F | Comfortable |
| May | 83.9°F | 67.7°F | 77.7°F | Warm |
| June | 88.3°F | 73.1°F | 80.8°F | Warm |
| July | 90.7°F | 74.9°F | 82.7°F | Bath-warm |
| August | 89.5°F | 74.9°F | 84.6°F | Bath-warm |
| September | 86°F | 73.2°F | 82.4°F | Bath-warm |
| October | 80.1°F | 65.3°F | 76°F | Warm |
| November | 72.4°F | 56.1°F | 70.4°F | Comfortable |
| December | 66.3°F | 49.4°F | 62°F | Brisk |
The ocean lags the air by about two months
Water has an enormous heat capacity, so the sea warms and cools far more slowly than the air above it. The result is a visible lag on the chart: the air peaks in July at 90.7°F, but the water does not peak until August. Going the other way, January is the coldest air but January is the coldest water.
That lag is why April catches people out. The afternoon reaches 77.4°F and feels like summer; the ocean is still 71.2°F and empties a swimmer out in a few minutes. It is also why October is the island's best-kept secret — 80.1°F air over 76°F water, the last of the summer heat still stored in the sea.
Our reading of the numbers
We group the months into bands. This is our judgement about the numbers, not a NOAA classification:
- Warm enough to stay in (77.7°F and above). May, June, July, August, September, October.
- Brisk but swimmable (68–75°F). April, November.
- Cold (below 68°F). January, February, March, December. Surfers wear a wetsuit; most people wade.
The island's annual mean sea temperature is 72.6°F.
Where these numbers come from, and their limits
The Fernandina Beach tide station on the island has no water-temperature sensor. We are not going to pretend otherwise, so the monthly figures on this page are means of three years of hourly readings — 2023 to 2025 — at the nearest NOAA sensor with a long record: Mayport (Bar Pilots Dock), FL, about 30 km south at the mouth of the St Johns River.
Two honest caveats. A river mouth is not open beach: it runs slightly cooler on an outgoing tide in winter and slightly warmer in a summer afternoon. And a monthly mean is not a forecast — the real ocean on a given day moves several degrees around it, mostly because of upwelling when the wind turns hard from the south-west.
For the temperature right now, the better source is the offshore waverider buoy: Offshore Fernandina Beach, FL, 17 km ENE, which reports water temperature alongside wave height. That is what feeds our surf report and beach conditions pages.
What actually decides whether it feels cold
Three things, in order:
- The gap between air and water. May has a 6.2°F gap and feels shocking; August has 4.9°F and feels like nothing at all.
- Wind. An onshore breeze on wet skin removes more heat than two degrees of sea temperature ever will.
- The tide. On a big outgoing tide the water leaving the sound and the creeks is the water that has been sitting in the shallows, which in summer is warmer and in winter is colder than the open ocean. See tides.
Every month in detail
Before you get in
Part of Amelia Island beaches.
Frequently asked questions
- What is the water temperature at Amelia Island?
- It averages 57.9°F in January and 84.6°F in August, for an annual mean of 72.6°F. For today's reading see our beach conditions page, which pulls from the NOAA buoy 17 km offshore.
- When is the ocean warm enough to swim at Amelia Island?
- From May to October the monthly mean is 77.7°F or above, which most people find warm enough to stay in. April and November are swimmable but brisk. January, February, March, December are cold.
- Why is the Atlantic colder here than in south Florida?
- Amelia Island is at the top of the state, roughly on the latitude of Jacksonville, and the Gulf Stream runs much further offshore here than it does off Palm Beach. The shelf water in between follows the seasons rather than the current, so the swing between winter and summer is far larger.
- Which station are these figures measured at?
- Mayport (Bar Pilots Dock), FL, NOAA CO-OPS station 8720218, about 30 km south of the island. The Fernandina Beach station has no water-temperature sensor, so there is no on-island long record to use. Real-time readings come from NDBC buoy 41112, 17 km ENE.