Come on in, the water’s nice and warm

Sun-seekers heading to the beach this summer are in for a postChristmas treat – balmy seas as warm as southern California or the Mediterranean.

Sea temperatures around the country are up to 3 degrees Celsius higher than the norm for this time of year, driven by months of hot weather and settled conditions.

Waters off Canterbury’s coasts are between 17C and 19C, similar to Long Beach in California, Greece and the holiday resorts of Tunisia in north Africa.

After a scorching Christmas Day in Christchurch, Boxing Day was drastically cooler, with temperatures in eastern Canterbury around 17C with some rain.

Temperatures in Christchurch are expected to be in the late teens and low 20s for much of the week,

"Ocean temperatures around the country are much warmer than usual for the time of year. At the moment, sea surface temperatures off the South Island are about 2 degrees Celsius above average for the time of year.'' Niwa forecaster Chris Brandolino

before rising to 27C on New Year’s Eve, according to the MetService.

Seas off the North Island are a lot warmer than those around southern coasts, according to the National Institute of Water and Atmospheric Research (Niwa).

Satellite data showed that as of December 21, sea surface temperatures around Auckland, the Bay Of Plenty and Waikato were around 21C to 23C – as hot as parts of the Gulf of Mexico.

Waves lapping the beaches of Mt Maunganui in Tauranga were 20C, while Hot Water Beach in Coromandel lived up to its name, touching 22C.

Swimmers dipping a toe into Lyall Bay in Wellington enjoyed waters of 17C, Kaiteriteri near Nelson reached 17C, while Sumner beach in Christchurch was 18C, Caroline Bay in Timaru was 16C and in Dunedin seas were around 15C.

The waters of the West Coast were unusually warm, with the sea around Greymouth and Westport touching 20C.

The hottest sea temperature in the world was at Nightcliff, near Darwin in Australia, which was 31.7C on Monday. .

Niwa forecaster Chris Brandolino said: ‘‘Ocean temperatures around the country are much warmer than usual for the time of year.

‘‘At the moment, sea surface temperatures off the South Island are about 2 degrees Celsius above average for the time of year.’’

The recent long spell of hot weather triggered the warmer seas. Sunshine and warm weather allow the sea’s surface to heat up, while settled conditions and little wind mean the top layer has not mixed with cooler waters beneath it, a process known as ‘‘upwelling’’.

Brandolino said: ‘‘Temperatures in the Tasman Sea, on the West Coast, are more unusually warm than the ocean temperatures on the Pacific side.

‘‘Both are warmer than usual and, looking forward, our expectation is that ocean temperatures around New Zealand will remain above average for the summer season.’’

Surf Life Saving New Zealand chief executive Paul Dalton urged people to plan their trips, choose patrolled beaches and always to swim between flags at beaches.

He said: ‘‘Take a moment to stop and think before entering the water and if in doubt, stay out.’’

For people wanting to swim in one of Canterbury’s lakes or streams, about 90 per cent of sites monitored by scientists are usually considered safe for swimming, Environment Canterbury says.