Sea temperature in United States
Live water temperatures and swimming conditions across 1075 beaches on the United States coast.
Best time to swim in United States
The sea in United States peaks in July, when the water averages around 28°C.
The main swimming season runs from April – November, when surface temperatures stay comfortable for extended sessions.
On average, 8 months a year sit above 20°C — the threshold most swimmers describe as pleasant without a wetsuit.
Shoulder months like March and December are noticeably cooler but often quieter, with fewer crowds and steadier weather.
The coldest month is typically January at around 18°C, when cold-water swimmers dominate the coast.
United States sea temperature history
Long-term climatology for United States shows an annual mean sea temperature of 23°C, ranging from 18°C in winter to 28°C at the summer peak.
The seasonal swing is roughly 10°C between the coldest and warmest month — a useful yardstick when comparing years or checking whether the current sea is running above or below average.
Recent decades have trended slightly warmer at United States, in line with regional sea-surface temperature records for the wider basin.
Monthly averages below are drawn from multi-decadal climatology and are updated as new observations arrive.
Values are area averages; individual beaches vary by exposure and depth.
United States sea temperature: frequently asked questions
What is the warmest month to swim in United States?
July is the warmest month in United States, when the sea averages about 28°C. Late-season warmth often persists a few weeks after peak.
When is the sea coldest in United States?
The coldest month in United States is typically January, when the water averages around 18°C. Cold-water swimmers and surfers dominate this period.
When can you swim in United States without a wetsuit?
The main swimming season in United States runs from April – November — about 8 months a year when the sea sits above 20°C, the level most swimmers describe as pleasant without a wetsuit.
Do I need a wetsuit in United States?
Outside peak summer the water in United States drops toward 19°C, so a 3/2mm shorty or full wetsuit makes long swims much more comfortable. In peak months most swimmers go without.
What is the average sea temperature in United States?
The long-term annual mean sea temperature in United States is about 23°C, based on multi-decadal climatology of the surrounding waters.
How do I check the current sea temperature in United States?
The live reading at the top of this page shows the current sea temperature in United States, updated hourly from marine buoy and satellite data. The 7-day forecast covers water, air, waves, wind and UV for the week ahead.
Browse by state
Deep-dive hubs for the US coastal states with the most tracked beaches.