Water temperature by month — Sebastian, Florida

The ocean off Sebastian Inlet averages about 72 degrees in late winter and 84 degrees in late summer, based on NOAA monthly averages for the stations north and south of the inlet.

NOAA does not publish a monthly water temperature average for Sebastian Inlet itself. Its Coastal Water Temperature Guide lists averages for stations on either side, and three of them frame the inlet: the CANAVERAL buoy 20 nautical miles east of Cape Canaveral, offshore and north of Sebastian; Trident Pier at Port Canaveral, a shallow nearshore site to the north; and the Lake Worth Pier to the south. The table below sets the three side by side.

Offshore, the Canaveral buoy bottoms out at 71.8 degrees in February and peaks at 84.0 in September. Lake Worth Pier, farther south, never averages below 74.5 degrees in January and reaches 85.7 in August. Sebastian Inlet sits between those two records along the coast, so a winter swimmer at the inlet faces water in the low 70s and a late summer swimmer water in the middle 80s.

Water off Sebastian Inlet warms fastest from March to June and cools fastest from October to December, and the nearshore water changes about twice as fast as the offshore buoy.

Spring warming off Sebastian is slow offshore and quick near the beach. The Canaveral buoy climbs from 72.0 degrees in March to 77.4 in May and 80.8 in June, a rise of 8.8 degrees in three months. Over the same months Trident Pier climbs from 74.4 to 82.8, after a jump of ten degrees between February at 68.9 and April at 78.9, according to the NOAA Coastal Water Temperature Guide.

Fall runs the other way. The offshore buoy holds 81.8 degrees in October, then slips to 78.7 in November and 75.6 in December. Trident Pier drops harder, from 81.0 in October to 74.5 in November and 70.3 in December. For Sebastian Inlet and the Sebastian Inlet State Park beaches, the result is a long warm-water season: on the NOAA averages, every month from May through November stays above 77 degrees offshore.

Nearshore water around Sebastian swings colder in winter and warmer in summer than the offshore buoy, as the Trident Pier averages show.

The Trident Pier record makes the point. Its January average is 66.8 degrees, about six degrees below the 72.9 at the Canaveral offshore buoy, while its September average of 87.0 runs three degrees above the buoy's 84.0. The two sites also measure at different depths: the Canaveral 20 NM buoy reads sea temperature 2 meters below the water line, while the nearshore wave buoys closer to Sebastian read it 0.46 meters down.

Readings taken on the same afternoon show the spread around Sebastian Inlet. At 2:56 p.m. on October 10, 2026, buoy 41114 off Fort Pierce reported 85.8 degrees, and buoy 41113 off Cape Canaveral reported 82.4. The Florida Tech monitoring station at Sebastian Inlet showed 79 degrees that day, and the NWS Melbourne Surf Zone Forecast put the water in the lower 80s for the Coastal Indian River beaches and in the mid 80s for the St. Lucie and Martin beaches to the south.

A swing of nearly seven degrees between the inlet and the Fort Pierce buoy on one October afternoon is the reason a single monthly figure for Sebastian Inlet would mislead. The monthly table gives the seasonal pattern; the live stations give the number for the day.

The Indian River Lagoon at Sebastian has reached 85 to 87 degrees in summer heat, while its coldest water comes in late February, but no agency publishes a monthly lagoon average for Sebastian.

Summer readings are the best documented. In August 2023, Sebastian Daily reported that the lagoon water had heated up to 85 degrees and that some local scientists reported 87 degrees during their studies, at a time when a minor fish kill had been reported in the lagoon. The same article noted that mangrove snapper were being seen at the north and south jetties of Sebastian Inlet that week.

The coldest water comes at the end of winter. A study of the Indian River Lagoon by Ned P. Smith of Harbor Branch Oceanographic Institution, published in Estuaries in 1983, compared bihourly water temperatures over two 110-day periods and found the annual minimum temperatures in late February. Cold snaps reach the shoreline in Sebastian, but the water lags the air: in February 2021, Sebastian Daily wrote that the water is usually warmer than the air temperature in cold weather, and put the lowest temperature seen that winter in the city at about 35 degrees.

Long records exist but are not summarized by month online. Harbor Branch's Technical Report 17 holds water temperature, salinity and dissolved oxygen collected approximately weekly from January 1972 through February 1975 in the Indian River between Sebastian and St. Lucie Inlets, published as tables. Limited public data are available for a current month-by-month lagoon average at Sebastian; further research is needed.

Live water temperatures for Sebastian are published by Florida Tech on the Sebastian Inlet District webcam page, by NOAA buoys 41114 and 41113, and in the daily NWS Melbourne surf forecast.

The Sebastian Inlet District webcam page carries a water temperature reading from the Florida Institute of Technology alongside the camera views and tide chart, and the Florida Tech research group's own page shows the same inlet reading with wave height, period and water level. Both come from the instruments Florida Tech maintains at the inlet with the Sebastian Inlet District.

For the open coast, the NWS Melbourne nearshore buoy page states that the Fort Pierce and Cape Canaveral wave buoys report sea surface temperature every hour, alongside wave height, period and direction. The Surf Zone Forecast adds a daily water temperature line for the Coastal Indian River beaches, from Vero Beach north through Melbourne Beach, which brackets Sebastian Inlet and the beaches of Sebastian Inlet State Park.

In winter the ocean off Sebastian is about ten degrees warmer than the average air temperature, while in late summer water and air run within a few degrees of each other.

The comparison uses two NOAA records. The 1991 to 2020 normals for the Vero Beach airport, the climate station nearest Sebastian, give a January mean air temperature of 62.8 degrees, against 72.9 degrees for January water at the Canaveral buoy and 74.5 at Lake Worth Pier. In August the Vero Beach air mean is 82.1 degrees, against 83.7 and 85.7 for the water.

That winter gap is why Sebastian Daily described the water as usually warmer than the air during cold snaps. By September the water at the Canaveral buoy averages 84.0 degrees, warmer than the Vero Beach September air mean of 80.9, so the warmest water of the year off Sebastian Inlet arrives after the hottest air.