Fire Island Water Temperature & Swim Forecast

The sea in Fire Island peaks in August, when the water averages around 23°C.

The main swimming season runs from July – September, when surface temperatures stay comfortable for extended sessions.

On average, 3 months a year sit above 20°C — the threshold most swimmers describe as pleasant without a wetsuit.

Shoulder months like June and October are noticeably cooler but often quieter, with fewer crowds and steadier weather.

Outside peak season the water drops toward 9°C, so a 3/2mm shorty or full wetsuit makes long swims much more comfortable.

The coldest month is typically February at around 3°C, when cold-water swimmers dominate the coast.

Long-term climatology for Fire Island shows an annual mean sea temperature of 12°C, ranging from 3°C in winter to 23°C at the summer peak.

The seasonal swing is roughly 20°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 Fire Island, 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.