Gulf of Maine Warming Update: Summer 2024

Reports | Oct 8, 2024

Over the past decade, scientists have led a body of research that highlights the rapid pace of warming in the Gulf of Maine. To help keep you informed, we share seasonal and annual updates about conditions in the Gulf of Maine. Read on for an inside look at what we've learned in our summer 2024 Gulf of Maine warming update.

Feature image for the 2024 summer warming report.

Summer Highlights

For this seasonal report we present an analysis of sea surface temperature (SST) in the Gulf of Maine for summer 2024, defined as the period extending from June 1, 2024 – August 31, 2024.

During the summer, Gulf of Maine SSTs reach their annual highs. For year-round resident species, summer can be a period of stress, as this is when SSTs are most likely to approach or exceed suitable temperature ranges. For other species, these same warmer summer temperatures open the door to seasonal travel into the area. Many species migrate into the Gulf of Maine to capitalize on a bounty of food that follows the spring phytoplankton bloom. For example, Atlantic bluefin tuna and various whales migrate hundreds of miles for a once-a-year feeding opportunity.

This summer the average SST for the Gulf of Maine was 61.13°F. This seasonal average temperature was 2.03°F above the 1991 – 2020 climatological reference period (CRP) summer average of 59.1°F, ranking as the seventh warmest summer on record since satellite SST observations began more than 40 years ago.

Weekly Temperatures

Table 1 highlights how the SST for each week this summer compares to the 1991 – 2020 CRP for the area shown in Figure 7 (see "About the Updates" section). The observed SST, long-term average SST, and SST anomaly (i.e., departure from the long-term average SST) are shown. The first half of June was particularly warm (~4°F above the long-term average) before temperatures moderated a bit for the rest of the summer, hovering around 1.5°F above the long-term average for the duration of the season.

Table 1. Observed weekly average SST, climatological average SST for that week, and SST anomaly (i.e., deviation from the climatological average) in the Gulf of Maine during summer 2024.
Table 1. Observed weekly average SST, climatological average SST for that week, and SST anomaly (i.e., deviation from the climatological average) in the Gulf of Maine during summer 2024.

Monthly Statistics

Table 2 shows monthly average SST for summer 2024. June SSTs exhibited the greatest positive deviation above the 1991 – 2020 CRP, with an average SST anomaly of 3.10°F, representing the second warmest June on record. SST anomalies fell to more modest levels during July and August, with each of these months ranking as the 11th warmest on record.

Table 2. Monthly ranking, observed average, climatological average, and deviation from the CRP average (i.e., temperature anomaly) for SST at a monthly resolution in the Gulf of Maine during summer 2024.
Table 2. Monthly ranking, observed average, climatological average, and deviation from the CRP average (i.e., temperature anomaly) for SST at a monthly resolution in the Gulf of Maine during summer 2024.

How Does this Summer Compare?

2024 was the seventh warmest summer season observed in the Gulf of Maine during the 42 years we have satellite data to analyze (Figure 1).

Figure 1. A ranking of the 20 warmest summer seasons for the Gulf of Maine in the satellite record (1982 – 2024). 2024 was the seventh warmest summer on record.
Figure 1. A ranking of the 20 warmest summer seasons for the Gulf of Maine in the satellite record (1982 – 2024). 2024 was the seventh warmest summer on record.

Seasonal Trends and Anomalies in Context

The Gulf of Maine is an area of particular interest to the scientific community because of the remarkable rate of warming it has experienced in recent years.

Figure 2 illustrates the average summer temperature anomaly for each year in the Gulf of Maine since the beginning of the satellite record in 1982, overlaid with long-term SST anomaly trends for the Gulf of Maine (orange) and global oceans (blue).

The summer rate of warming for the Gulf of Maine (1.04°F per decade) is roughly 4x faster than the summer warming rate for the oceans, globally (0.27°F per decade).

Figure 2. Average annual summer SST anomalies in the Gulf of Maine from 1982 – 2024 (black dots). The orange line indicates the trend for the full timeseries for the Gulf of Maine. The blue line indicates the trend for the full timeseries for the global oceans.
Figure 2. Average annual summer SST anomalies in the Gulf of Maine from 1982 – 2024 (black dots). The orange line indicates the trend for the full timeseries for the Gulf of Maine. The blue line indicates the trend for the full timeseries for the global oceans.

Marine Heatwave Conditions

The most commonly used definition of a “marine heatwave” (MHW) is when daily average SSTs exceed the 90th percentile of a climatological (i.e., 30-year) average for at least five consecutive days. Gaps of two days or less in reaching this threshold do not constitute a break in a single MHW event. Using this broadly accepted definition, the Gulf of Maine experienced MHW conditions for 26% of days this summer. These days were all part of a single MHW event that began at the end of May and extended through much of June.

Figure 3. A timeseries of marine heatwave (MHW) conditions in the Gulf of Maine extending from January 1, 2024 through August 31, 2024. Black lines represent the long-term (i.e., 1991 – 2020) average SST, the 10th percentile, and 90th percentile for a given day in the Gulf of Maine; a solid line (red for marine heatwave or blue for non-heatwaves) indicates the observed SST this year; red (above 90th percentile) and blue (below 90th percentile) shading illustrates how far the observed SST is from the climatological average.
Figure 3. A timeseries of marine heatwave (MHW) conditions in the Gulf of Maine extending from January 1, 2024 through August 31, 2024. Black lines represent the long-term (i.e., 1991 – 2020) average SST, the 10th percentile, and 90th percentile for a given day in the Gulf of Maine; a solid line (red for marine heatwave or blue for non-heatwaves) indicates the observed SST this year; red (above 90th percentile) and blue (below 90th percentile) shading illustrates how far the observed SST is from the climatological average.

Heatmap of Temperature Anomalies and Heatwave Events

Looking at the full record of daily SST anomalies in the Gulf of Maine (Figure 4), a distinct thermal regime shift beginning around 2010 is evident. Indeed, since 2012, the Gulf of Maine has experienced far more persistent and intense warm anomalies (deep red color bars) and MHW conditions (indicated by solid black lines) than at any other point in the satellite record.

Summer SSTs in the Gulf of Maine have been warming more rapidly than other seasons (see Fig. 8 of our 2023 Annual Warming Update), and extended MHW events during this time of year have become common. This was the case again in 2024, with the only heatwave of the year to date occurring during the summer months.

Figure 4. Heat map of daily SST anomalies from the beginning of 1982 through August 2024. Not only do large warm anomalies (darker reds) appear more frequently in recent years, but the frequency, duration, and intensity of marine heatwave events (black lines) in the Gulf of Maine has become more pronounced in the past decade.
Figure 4. Heat map of daily SST anomalies from the beginning of 1982 through August 2024. Not only do large warm anomalies (darker reds) appear more frequently in recent years, but the frequency, duration, and intensity of marine heatwave events (black lines) in the Gulf of Maine has become more pronounced in the past decade.

Spatial Distribution of Seasonal Anomalies

When viewed spatially, above-average SST anomalies were distributed fairly evenly across the Gulf of Maine region during summer 2024 (Figure 5). Two areas of below average conditions located off the southern tip of Nova Scotia or to the southeast of Cape Cod were the exceptions to otherwise above-average summer conditions. The highest seasonally averaged SST anomaly in the Gulf of Maine was 2.29°F — located near Penobscot Bay in Maine.

Figure 5. Map of average SST anomalies for each grid cell in the satellite record for summer 2024. The box outlined by the black dashed line denotes the region of study for the analysis (see Figure 7). Darker red regions indicate warmer anomalies. Black contours have been added at 100m and 200m depths.
Figure 5. Map of average SST anomalies for each grid cell in the satellite record for summer 2024. The box outlined by the black dashed line denotes the region of study for the analysis (see Figure 7). Darker red regions indicate warmer anomalies. Black contours have been added at 100m and 200m depths.

Spatial Distribution of Monthly Temperature Anomalies

Monthly average SST anomalies for summer 2024 are shown spatially in Figure 6. During June, above-average SSTs were present for much of the regional continental shelf, with below-average SSTs present off-shelf and over central Georges Bank. By July, below-average SSTs had developed off the southern edge of Nova Scotia and along the western Gulf of Maine coast, with the cold anomaly strengthening over Georges Bank. This general spatial set up of SSTs in July persisted through August.

Figure 6. This series of maps shows the monthly average SST anomaly for June, July, and August 2024. The box outlined by the black dashed line denotes the region of study for the analysis. Darker red regions indicate warmer anomalies.
Figure 6. This series of maps shows the monthly average SST anomaly for June, July, and August 2024. The box outlined by the black dashed line denotes the region of study for the analysis. Darker red regions indicate warmer anomalies.

About the Updates

The Gulf of Maine Region

For analyses like these, it is important to be clear about the spatial extent that “defines” the Gulf of Maine (Figure 7), as different borders could produce different results. The spatial domain we use as the “Gulf of Maine'' is displayed below. This area is consistent with previous seasonal and annual Gulf of Maine warming reports produced by GMRI.

Figure 7. Spatial domain used for Gulf of Maine SST analyses. Depth contours are colored at 100m intervals up to 600m; deeper blues indicate deeper water depths.
Figure 7. Spatial domain used for Gulf of Maine SST analyses. Depth contours are colored at 100m intervals up to 600m; deeper blues indicate deeper water depths.

A Note on Data Sources

The figures in this report are created using remotely-sensed satellite data as part of publicly funded research efforts. Satellite sea surface temperature (SST) data was obtained from NOAA’s National Center for Environmental Information (NCEI), with all maps and figures displaying NOAA’s Optimum Interpolation Sea Surface Temperature Data.http://www.gmri.org/stories/gulf-of-maine-warming-update-summer-2024

NOAA_ERSST_V5 data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA.

NOAA High Resolution SST data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA.

Citing This Work

If you would like to cite this report, please use:

Gulf of Maine Research Institute. 2024. Gulf of Maine Warming Update: Summer 2024 www.gmri.org/stories/gulf-of-maine-warming-update-summer-2024.

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