Ocean water temperatures around Maritimes reaching record highs for July

A remarkable warming of ocean waters this July has some of the Atlantic marine districts reaching record highs.

Data provided by Peter Galbraith, a research scientist with the Department of Fisheries and Oceans (DFO), shows the average sea surface temperature in July is reaching record highs for eastern areas of the Grand Banks, the waters off the South Shore of Nova Scotia, and parts of the Bay of Fundy.

The waters off the South Shore of Nova Scotia, including parts of Lahave Bank and the Scotian Slope, are particularly remarkable. There the expected average for July 2023 is 17.4 C. That currently exceeds the standing record of 15.5 C set in 2022 by nearly 2 degrees. The Bay of Fundy is sitting at 14.85 C which is just over the record of 14.81 C set in 2022.

Warm ocean waters are now present around the Maritimes. Most of these temperatures shown running 1 to 4 degrees above average for the month of July.

There has been a marked turnaround in sea surface temperature anomaly from June to July for our ocean areas. While North Atlantic water temperatures were found to be at record highs in June most of our marine districts were actually sitting at or slightly below average for the month. Now halfway through July, according to data from the National Oceanographic and Atmospheric Association and DFO, most of those districts are sitting at 1 to 4 degrees above the monthly average.

A sea surface temperature anomaly chart from June 20, 2023. The white and blues around the Maritimes indicating temperatures near or below average.

A sea surface temperature anomaly chart from July 18, 2023. The reds around the Maritimes indicating temperatures well above average a marked difference from June.

What is the cause of the turnaround? According to Peter Galbraith sea surface temperatures in the western Atlantic are primarily influenced by atmospheric conditions, in other words, the weather.

From June into July the northern hemisphere has experienced several stagnant ridges in the jet stream. Those ridges have allowed heat domes to form allowing for extreme heat that has broken records in the southern US, southern Europe, and parts of the Middle East and Asia.

A map from the UK Meteorological Office showing the current locations of the heat domes in the northern hemisphere.

While the Maritimes isn’t under one of those heat domes we have had a persistent ridge that has run up the eastern seaboard of the US and north of Atlantic Canada. That has allowed for a persistent southerly flow in the atmosphere moving very warm, humid air up from the subtropical Atlantic. The presence of that subtropical air warms the surface waters under it.

Waters could cool in the event of a cooler round of air arriving or, in the case of near coastal waters, a strong storm to create upwelling. Upwelling is the movement of cooler water at depth toward the surface. Neither of those scenarios look likely over the next several days and so the expectation is that by the end of July, our ocean waters will continue to be well above climate averages.