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Water temperature below average

The water off Gisborne's beaches is warming a little more slowly than usual, despite claims of a marine heatwave looming in New Zealand's coastal waters.

The water temperature yesterday stood at 18.5 degrees — well below the average of 19.1 for Gisborne beaches in January.

New Zealand last experienced a marine heatwave in 2018 when some coastal waters reached as much as 2 or 3 degrees above normal. Far North beaches recorded water as warm as 25.

There is talk of another marine heatwave in some quarters but satellite and other measurements are not indicating anything other than the usual summer warming.

Typically western coast waters fronting the Tasman Sea are warming ahead of eastern coasts, where a south-to-north current keeps things cooler, with the peak warmth in February.

Unusually, towards the end of 2020, a large blob of warm water developed in the Pacific 1500 kilometres east of New Zealand, past the Chatham Islands.

This was up to 3 degrees warmer than usual, but now appears to be dissipating.

Sea temperatures provided on a daily basis by various agencies, including Niwa, MetService and the US National Oceanic and Atmospheric Administration, show no warming of the Tasman that would indicate New Zealand's coasts are about to experience above normal warm water.

It is well known the oceans act as a heat sink, soaking up solar energy, with each hemisphere warming in turn as the seasons progress. However, it takes longer for the sea to heat up than the land or atmosphere, which is why the peak of summer heat lags behind the calendar summer.

Gisborne's record for warm water is 21.7 degrees for January and 22.4 for February.

Niwa says New Zealand's coast waters have warmed by 0.2 of a degree every 10 years since the 1980s, with the warming particularly evident off the South Island's West Coast and Wairarapa.

For Gisborne, the yearly mean air temperature over land has risen from 14.2 in the sixties to 15.2 for 2020. — RH