Weather: Coastal sea temperatures around New Zealand well above average for time of year

With summer starting on Wednesday, beachgoers are in for a treat with coastal sea temperatures around New Zealand well above average for this time of year.

Water temperatures have ranged from 1.1C to 1.4C above average for November according to NIWA meteorologist Ben Noll.

The daily sea surface temperatures are also up more than 3C on average around the western and northern North Island and eastern South Island over the last week.

Marine heatwave conditions - classified when the sea temperature is above the 90th percentile for at least five days - have been observed in waters offshore of all regions of New Zealand.

This is comparable to the conditions observed in November 2017, which marked the beginning of an unprecedented marine heatwave around the country and in the Tasman Sea.

"Frequent patterns of high pressure near and south of New Zealand during November, owing to La Niña, have caused more frequent sub-tropical, northeasterly winds than normal," Noll says. "Reduced wind speeds through the month have prevented colder, subsurface ocean waters from getting mixed up to the surface. 

"In addition, sunshine has generally been above normal, which has helped to heat the ocean surface."

Marine heatwaves are becoming increasingly more common as New Zealand has experienced a warmer climate over the last decade. 

There have been 963 marine heatwave days observed in the New Zealand region between 2010-2019 compared to 366 between 2000-2009.