North Wales

The sea in North Wales peaks in August, when the water averages around 17°C.

On average, 0 months a year sit above 20°C — the threshold most swimmers describe as pleasant without a wetsuit.

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 8°C, when cold-water swimmers dominate the coast.

Long-term climatology for North Wales shows an annual mean sea temperature of 12°C, ranging from 8°C in winter to 17°C at the summer peak.

The seasonal swing is roughly 9°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 North Wales, 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.