Water temperature in Onset (MA) in August

Is it warm enough to swim in Onset in August? Average water temperature in Onset in August is 72.3°F and therefore suitable for comfortable swimming. The warmest sea in Onset in August is 79.7°F, and the coldest is 65.5°F. To find out the sea temperature today and in the coming days, go to Current sea temperature in Onset

Changes water temperature in Onset in August 2025, 2024

To get an accurate forecast for the water temperature in Onset for any chosen month, compare two years within a 10 year range using the chart below. In addition to the sea water temperature in Onset, the selected years in the table also show the values of the maximum and minimum temperatures on each of the days of August.

Average water temperature in Onset in August over a decade

Chart comparing the height of waves in Onset in August over the past years. The red line indicates the height of the waves when swimming in the sea is prohibited. To view the current sea conditions, click on the graph.

You can also view information about water temperature for other months by clicking on the month button below

The nearest locations with the average water temperature in August. In addition, the maximum and minimum water temperatures for that month, recorded over the last decade, are shown

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Our report for Onset is compiled using satellite data together with in-situ observations to get the most reliable daily data of sea surface temperatures, surf forecasts, current temperatures and weather forecasts.