Nantasket Beach Water Temperature
The ocean off Nantasket Beach averages about 66°F in July and 67°F in August, the warmest months. June averages about 61°F and September about 65°F. Those figures come from NOAA's Boston buoy (station 44013) for the summers of 2023 to 2025. For today's reading, check the buoy's live page.
Ocean Temperature, May to October
Average sea surface temperature at NOAA buoy 44013, 2023 to 2025. Worked out from NOAA's historical data.
Where to Check Today's Water Temperature
NOAA's National Data Buoy Center runs station 44013, a buoy about 16 nautical miles east of Boston in Massachusetts Bay. It reports the sea surface temperature through the day, and its station page shows the latest reading. This is the nearest public, official water temperature reading we know of for Nantasket.
Keep in mind what the number is. The buoy floats in open water well offshore, not in the surf at Hull. Water at the beach can run warmer or colder than the buoy on any given day, so use it as a guide, not a promise.
Nantasket Water Temperature by Month
We worked out these averages from every reading the buoy logged in 2023, 2024 and 2025, using NOAA's historical data files. That's more than 13,000 readings for each summer month.
- May: about 52°F on average, with readings from 45.5°F to 63.1°F. Cold for a swim.
- June: about 61°F, ranging from 51.1°F to 71.4°F. The water warms fast through the month.
- July: about 66°F, ranging from 59.0°F to 74.5°F.
- August: about 67°F, ranging from 60.4°F to 73.0°F. The warmest month on average.
- September: about 65°F, ranging from 60.3°F to 75.7°F. The highest single reading in the three years came in September.
- October: about 59°F, ranging from 54.9°F to 65.3°F.
Years differ. July averaged 67.6°F in 2023, 63.9°F in 2024 and 67.2°F in 2025, so one summer can run a few degrees cooler than the next.
Water vs. Air in Summer
In July, NOAA's 30-year normal high at Boston Logan is about 82°F, while the water off Hull averages about 66°F. That gap of about 16 degrees is why the water feels cold on a hot day. By September the gap shrinks: the normal high drops to about 73°F, but the water still averages about 65°F. Our Weather page has the full air temperature table.
Planning a Swim
- Lifeguards: on duty Memorial Day to early September (weekends only until June 18). Late May and early June bring the coldest water of the guarded season. Dates and hours are on our Hours page.
- Water quality: the state tests the water at Nantasket through the season. See our Water Quality page before you go in.
- Tides: at high tide much of the beach is under water. Our Tides page shows where to find the day's times.
Summer Water at Nantasket
Water Temperature FAQ
How cold is the water at Nantasket Beach?
In summer, about 61°F in June, 66°F in July, 67°F in August and 65°F in September, based on NOAA's Boston buoy (station 44013) for 2023 to 2025. May averages about 52°F.
What is the water temperature at Nantasket Beach today?
Check NOAA buoy 44013, about 16 nautical miles east of Boston. Its station page shows the latest sea surface reading. Water at the beach can differ from the buoy.
When is the water warmest at Nantasket?
August, at about 67°F on average, with July close behind at about 66°F. The single warmest reading from 2023 to 2025 came in September, at 75.7°F.
Is Nantasket water warm enough to swim in June?
June averages about 61°F at NOAA's Boston buoy, with readings from 51°F to 71°F. It warms through the month, so late June is usually warmer than early June.