Gulf of Maine Warming Update: Fall 2024

Reports | Jan 17, 2025

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 fall 2024 Gulf of Maine warming update.

fall 2024 warming update feature image

Fall Highlights

For this seasonal report we present an analysis of sea surface temperature (SST) in the Gulf of Maine for fall 2024, defined as the period extending from September 1, 2024 – November 30, 2024. This year, the average SST for the Gulf of Maine was 57.86°F. These conditions are 1.33°F above the 1991 – 2020 climatological reference period (CRP) average of 56.53°F, and place 2024 at the tenth warmest fall on record. Fall SST anomalies were highest (but variable) from September through mid-November, and they dropped below the long-term climatological average at the end of fall.

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 fall 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 fall 2024.

Monthly Statistics

Table 2 shows monthly average SST for fall 2024. September and October SSTs each were within the top ten warmest for their respective months. November was comparatively cool with SSTs within 0.5°F of the climatological average.

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 fall 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 fall 2024.

How Does this Fall Compare?

2024 was the 10th warmest fall season observed in the Gulf of Maine during the 42 years satellite data is available (Figure 1).

Figure 1. A ranking of the 20 warmest fall seasons for the Gulf of Maine in the satellite record (1982 – 2024). 2024 was the tenth warmest fall on record.
Figure 1. A ranking of the 20 warmest fall seasons for the Gulf of Maine in the satellite record (1982 – 2024). 2024 was the tenth warmest fall 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 fall 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 fall rate of warming for the Gulf of Maine (1.08°F per decade) is roughly four times faster than the fall warming rate for the oceans, globally (0.27°F per decade).

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

This fall’s sea surface temperature (SST) anomaly is higher than in 2023 but remains well below the elevated anomalies observed from 2020 to 2022 (Figure 2 above). Several factors likely contributed to this difference, with air temperature playing a key role.

Energy is exchanged between the ocean and atmosphere, meaning warmer-than-normal air temperatures can transfer more heat to the ocean, driving warming. During the falls of 2020 to 2022, air temperatures over the Gulf of Maine were notably warmer than in 2024, contributing to higher SST anomalies. In contrast, fall 2023 had cooler air temperatures, resulting in a lower SST anomaly than 2024.

Another contributing factor may have been sunlight. The falls of 2020 to 2022 likely experienced reduced cloud cover, allowing more sunlight to reach the ocean surface and further elevate SSTs.

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 has experienced MHW conditions for 10% of days this fall. These days were from a single 9-day MHW event that began at the end of September and extended through the beginning of October.

Figure 3. A time series of marine heatwave (MHW) conditions in the Gulf of Maine extending from January 1, 2024 through November 30, 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 time series of marine heatwave (MHW) conditions in the Gulf of Maine extending from January 1, 2024 through November 30, 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 and fall 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 two heatwaves of the year to date occurring during the summer and fall months. However, this

Figure 4. Heat map of daily SST anomalies from the beginning of 1982 through November 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 November 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 fall 2024 (Figure 5). This fall’s SST anomalies were evenly distributed and just above the climatological average. During this same time, seasonal high and low SST anomaly areas were located to the south of the Gulf of Maine region.

Figure 5. Map of average SST anomalies for each grid cell in the satellite record for fall 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, and darker blue regions indicate cooler 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 fall 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, and darker blue regions indicate cooler anomalies. Black contours have been added at 100m and 200m depths.

Spatial Distribution of Monthly Temperature Anomalies

Monthly average SST anomalies for fall 2024 are shown spatially in Figure 6. During September, above-average SSTs were located towards the interior of the Gulf of Maine, particularly over its deep basins. Below-average SSTs were present off of Nantucket and off the southern tip of Nova Scotia. In October, SST anomalies across the Gulf of Maine were warm. At this time, two contrasting hot and cold water masses had developed to the south of Georges Bank and the shelf-break. During November, SST anomalies along the Scotian Shelf and the eastern Gulf of Maine had cooled with the expansion of cold-water anomalies throughout the Scotian shelf.

Figure 6. This series of maps shows the monthly average SST anomaly for September, October, and November 2024. The box outlined by the black dashed line denotes the region of study for the analysis. Darker red regions indicate warmer anomalies, and darker blue regions indicate cooler anomalies.
Figure 6. This series of maps shows the monthly average SST anomaly for September, October, and November 2024. The box outlined by the black dashed line denotes the region of study for the analysis. Darker red regions indicate warmer anomalies, and darker blue regions indicate cooler 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

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

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.

Citing This Work

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

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

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