Sea Surface Temperature Update - 13 February 2019

A fortnightly report, updated over summer, covering sea surface temperatures and anomalies (differences from average) around New Zealand.

Following the Tasman Sea marine heatwave event of 2017-18, this report will help users understand the latest conditions in the ocean and their expected changes over the upcoming weeks.

Recent sea surface temperatures and anomalies

Over the past two weeks, sea surface temperatures (SSTs) have increased in the New Zealand and Tasman Sea region.

As a whole, Tasman Sea surface temperatures are +1.5˚C above average for the time of year, although localized anomalies of +2.0 to +3.0˚C exist in the central and west. This is an increase of +0.2˚C compared to the previous two week period.

New Zealand coastal waters are generally 0.5˚C to 1.5˚C above average, although anomalies of +2.0 to 3.0˚C are occurring in pockets near Southland, Otago, and Canterbury. Meanwhile, SSTs near Wellington are near or slightly below average for the time of year.

Marine heatwave conditions are still likely occurring in parts of the central and western Tasman Sea, according to the definition proposed by Australian research in 2016 (see background below). The existence of marine heatwave conditions may influence ex-tropical cyclones should they track toward the region in the coming weeks to months.

Compared to early 2018, current SSTs in the Tasman Sea are similar. While the peak observed near the end of January 2018 has not occurred in 2019, conditions have persistently been well above average (see figure 1 below).

Expected conditions over the next several weeks  

Another very hot air mass is currently sitting over New Zealand, which will lead to additional SST warming over the next few days. For the South Island, a southerly change will result in some cooling over the weekend. Warmer weather will return countrywide next week, followed by a potential colder change toward the end of the month. While sea surface temperatures are expected to remain above average for the time of year, marine heatwave conditions are unlikely to develop in new areas.

Background:

Sea Surface Temperature Update is a fortnightly report for New Zealand media. It provides measurements of sea surface temperature and anomalies (differences from average) measurements for New Zealand coastal and Tasman Sea waters.

Sea surface temperature anomaly: the difference between the long-term (1981-2010) average sea surface temperature and current sea surface temperature for a given time of year.

New Zealand region: within this document, any quoted anomalies refer to spatial averages over the ocean region bounded by the coordinates (145°E-175°W, 25-55°S)

SST: abbreviation for sea surface temperature.

Marine heatwave: periods of extremely warm sea surface temperature that persists for a prolonged period of time and can extend up to thousands of kilometres. According to Australian research (Hobday et al. 2016), warm sea surface temperature events are considered marine heatwaves (MHWs) if they last for five or more days with temperatures warmer than the 90th percentile based on a 30-year historical baseline period.

Research subject: Oceans