Louisiana Coast
Grand Isle Water Temperature
Louisiana's only inhabited barrier island, and the state's most famous fishing town.
That is about 6°F warmer than average for this time of year, and cooling over the last two weeks. The October average here is 79°F.
Updated Saturday, October 3 — sea-surface temperature modeled for Grand Isle by Open-Meteo.
Out in the open Gulf, NOAA buoy 42084 — 27 miles offshore — is reading 85°F. Deep water offshore runs cooler than the shallows in summer and warmer in winter, so it won't match the beach.
For swimming
Very warm
Bath-warm. Pleasant, though it stops being much relief from the heat of the day.
For fishing
Hot — fish the edges of the day
Early and late is the play. Through the middle of the day fish drop into deeper channels and passes where there's moving water and more oxygen.
The last two weeks
Daily average sea-surface temperature, °F.
Grand Isle water temperature by month
Averaged from 3 years of daily sea-surface temperature (2023–2025). The range column is the coolest and warmest daily average recorded in that month over the period — a guide to how much any given year can differ, not a record high and low.
| Month | Average | Range | Swimming |
|---|---|---|---|
| January | 60°F | 55–66°F | Bracing |
| February | 62°F | 57–69°F | Bracing |
| March | 68°F | 64–75°F | Cool but comfortable |
| April | 73°F | 69–79°F | Cool but comfortable |
| May | 80°F | 73–85°F | Warm |
| June | 85°F | 83–88°F | Very warm |
| July | 88°F | 87–90°F | Bath water |
| August | 89°F | 86–91°F | Bath water |
| September | 85°F | 82–89°F | Very warm |
| Octobernow | 79°F | 75–84°F | Warm |
| November | 73°F | 65–78°F | Cool but comfortable |
| December | 65°F | 60–70°F | Bracing |
Warmest on average in August at 89°F; coolest in January at 60°F.
The water at Grand Isle
Grand Isle is the one inhabited barrier island Louisiana has, a narrow strip of sand and camps with the Gulf on one side and Barataria Bay behind it. The state's fishing culture concentrates here — a summer tarpon rodeo tradition going back generations, surf and pier fishing off the beach, speckled trout and redfish on the bay side, and offshore structure within reach of a well-found boat. The beach draws campers, swimmers and birders, and the island's position out ahead of everything else makes it a first landfall for songbirds crossing the Gulf in spring. Sitting that far out cuts both ways: storms come ashore here directly, and the marsh behind the island has been thinning for decades.
Barataria Bay & the Gulf
What moves the water temperature here
The Gulf shelf off this coast is shallow, which is why the water swings so much more between summer and winter than open ocean at the same latitude does. Shallow water heats fast and gives that heat up fast: a single strong winter cold front can pull the inshore bays several degrees down in a couple of days, while the beaches a mile offshore barely move. Wind direction matters too — a sustained offshore breeze can pull cooler water up from below and drop the beach temperature noticeably in a morning.
Inshore bays, canals and flats run warmer than the beach through the summer and colder through the winter, for the same reason. The reading above is for the open water at Grand Isle; expect the back bays to be a few degrees either side of it depending on the season.
Common questions
- What is the water temperature at Grand Isle right now?
- The water at Grand Isle is currently about 85°F (29°C). The October average here is 79°F.
- Is the water warm enough to swim at Grand Isle in October?
- October averages 79°F at Grand Isle, which most people would call warm. About as good as it gets — warm enough to stay in for hours without getting chilled.
- When is the water warmest at Grand Isle?
- August is the warmest month on average at 89°F, and January the coolest at 60°F. 6 months of the year average 75°F or above.
- Why does the water temperature change so quickly here?
- The Gulf shelf off this coast is shallow, so it heats and cools far faster than deep open ocean. A strong winter cold front can pull the inshore water down several degrees in a couple of days, and a sustained offshore wind can drop beach temperatures in a single morning by pulling cooler water up from below.