New research shows sea surface temperatures (SSTs) are up to 3degC warmer than they were this time last year.
The 'snapshot in time' sea maps were taken last week, and the equivalent period in 2017.
They show Auckland's SSTs are currently around 19degC-20degC, compared to 17degC in 2017. Wellington is up one to 15degC, while Christchurch is up two to 15degC.
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NIWA meteorologist Seth Carrier told Newshub the warm water is due to high pressure delivering tranquil weather recently.
"Until the last couple of days, New Zealand has experienced generally tranquil weather recently due to high pressure over the region," he says.
"Such settled weather prevents different layers of the ocean from mixing together - mixing tends to keep water temperatures lower.
"Due to the settled weather, SSTs were able to increase more easily."
Unfortunately, a low pressure system this week has brought much cooler air, leading to a decrease in water temperatures. But things should warm up next month.
"Looking farther into the future, warmer and more settled weather is favoured during early and mid-December - so that may be a good time to head to the beach," Mr Carrier says.
"Unfortunately the second half of December may be a bit cooler, particularly in the South Island.
"As of now, January could bring fairly settled conditions and warmer temperatures to New Zealand."
Newshub.
