Sea Surface Temperature Update - 16 January 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 several weeks, the sea surface temperatures (SSTs) have warmed in the New Zealand region. SSTs are well above average in the Tasman Sea with anomalies of +2.0˚C to 4.0˚C, and also above average in New Zealand coastal waters with anomalies of +1.0 to 3.0˚C. Compared to the exceptional conditions at this time last year, SSTs are even warmer to the north and east of New Zealand and about equally as warm in the Tasman Sea (image below).

Given that SSTs have been significantly warmer than average for several weeks, marine heatwave conditions are likely now occurring in parts of the Tasman Sea and New Zealand coastal waters, according to the definition proposed by Australian research in 2016 (see background below).

Expected Conditions over the Next Several Weeks

Over the next week, a hot air mass is forecast to persist over eastern Australia and the western Tasman Sea. This should lead to additional, short-term SST warming. During the last week of the month, there is the potential for a few low-pressure systems to track near or south of Tasmania, which could initiate a period of slightly cooler than average air temperatures and a reduction in sea surface temperatures.

For New Zealand, periods of mainly warmer than normal temperatures are forecast over the next two weeks along with a few southerly changes. During that time, SSTs and anomalies may warm slightly near the North Island and cool slightly or remain the same near the South Island.

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: Climate