Coastal sea temperatures around Aotearoa New Zealand have risen well above average, NIWA forecasters say.
Marine heatwave conditions, classified when the sea temperature is above the 90th percentile for at least 5 days, have been observed in waters offshore of all regions of New Zealand.
Meteorologist Ben Noll says that water temperatures have ranged from 1.1˚C to 1.4˚C above average for the month of November, with daily sea surface temperatures being more than 3˚C above average around the western and northern North Island and eastern South Island over the last week.
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 sub-tropical, northeasterly winds than normal. Reduced wind speeds through the month have prevented colder, subsurface ocean waters from getting churned 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 frequent in a warmer climate with 963 marine heatwave days observed in the New Zealand region between 2010-2019 compared with 366 between 2000-2009.
“NIWA’s Seasonal Climate Outlook for summer will be released tomorrow, providing commentary on the likelihood of warm seas continuing through the season and their impact on the summer ahead.”