Gulf of Maine Warming Update: Winter 2024–25

Reports | Apr 10, 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 winter 2024 – 25 Gulf of Maine warming update.

Winter 2024-25 Gulf of Maine Warming Update

Winter Highlights

For this seasonal report, we present an analysis of sea surface temperature (SST) in the Gulf of Maine for winter 2024 – 25, defined as the period extending from December 1, 2024 – February 28, 2025.

Winter is an important time of year for the Gulf of Maine. During this time of year, SSTs are typically falling, weakening the stratification of surface waters from deeper waters that occurs during warmer months. The breakdown of stratification allows for vertical mixing in the water column, which helps transport important nutrients up into the near-surface waters. These nutrients fuel the spring phytoplankton blooms that support the high productivity in the region. Vertical mixing may be enhanced in winter with the help of Nor’easters, which are most frequent this time of year and stir up the water column with rough seas and strong winds.

This winter, the average SST for the Gulf of Maine was 43.16°F. These conditions were 0.88°F below the 1991 – 2020 climatological reference period (CRP) average of 44.04°F, which places this winter as the 26th warmest (or the 19th coldest) on record.

Weekly Temperatures

Table 1 highlights how the SST for each week this winter compares to the 1991 – 2020 CRP for the area shown in Figure 7 (see "About the Updates" section) The weekly observed SST, long-term average SST, and SST anomaly (i.e., departure from the long-term average SST) are reported in the table.

Temperature anomalies were below the long-term average for every week of the winter, with weekly anomalies ranging from -0.12°F to -1.92°F.

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 winter 2024 – 25.
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 winter 2024 – 25.

Monthly Statistics

Table 2 shows monthly average SST for the 2024 – 25 winter season. Monthly conditions were below the long-term average for each month. February SSTs were coldest, averaging 1.07°F below the 1991 – 2020 long-term 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 winter 2024 – 25.
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 winter 2024 – 25.

How Does this Winter Compare to Past Winters?

Winter 2024 – 25 was the 26th warmest (19th coldest) winter season observed in the Gulf of Maine during the 44 years satellite data are available (Figure 1).

Figure 1. A ranking of the 30 warmest winter seasons for the Gulf of Maine in the satellite record (1982 – 2024). Winter of 2024 – 25 was the 26th warmest (19th coldest) on record.
Figure 1. A ranking of the 30 warmest winter seasons for the Gulf of Maine in the satellite record (1982 – 2024). Winter of 2024 – 25 was the 26th warmest (19th coldest) 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 winter 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 long-term rate of warming in winter for the Gulf of Maine (0.66°F per decade) is three times faster than the winter warming rate for oceans globally (0.22°F per decade).

Figure 2. Average annual winter SST anomalies in the Gulf of Maine from 1982 through 2024 – 25 (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 winter SST anomalies in the Gulf of Maine from 1982 through 2024 – 25 (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.

Extreme Temperature Conditions

A “marine heatwave” (MHW) is defined by daily average SSTs that exceed the 90th percentile of a climatological (i.e., 30-year) average for at least five consecutive days. A “marine coldspell” (MCS) event is the cold-temperature counterpart to a MHW, and is identified using the same approach, but for temperatures below the 10th percentile. Gaps of two days or less in reaching the threshold do not constitute a break in a single MHW/MCS event.

Using these broadly accepted definitions, this winter the Gulf of Maine experienced no MHW conditions, but did experience nine days of MCS conditions, accounting for 10% of the days this winter. MCS conditions are from a single nine day event that began on February 20th, lasting through the end of the month.

Figure 3. A time series of SSTs in the Gulf of Maine extending from December 1, 2024 through February 28, 2025. 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, lightblue for marine coldspells, or blue for non-event SSTs) 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. We observed one nine day marine coldspell at the end of the winter period.
Figure 3. A time series of SSTs in the Gulf of Maine extending from December 1, 2024 through February 28, 2025. 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, lightblue for marine coldspells, or blue for non-event SSTs) 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. We observed one nine day marine coldspell at the end of the winter period.

Using our standard definition, last year (2024) was a mild year with respect to MHW conditions, with just two short MHW events occurring during the warmer months (Figure 4). Summer and fall SSTs in the Gulf of Maine have been warming more rapidly than other seasons (see Fig. 5 of our 2024 Annual Warming Update), and extended MHW events during this time of year have become common, which may relate to water column stratification during these months.

2025 is off to a similar start to 2024, with below-average over-winter SST’s, but with the added development of a MCS. MCS conditions in the Gulf of Maine have been rare occurrences since the shift in ocean temperatures around 2010. The most recent MCS event occurred in 2019, the next closest a full decade earlier.

Figure 4. Heat map of daily SST anomalies from a 1991 – 2020 climatological baseline from the beginning of 1982 through February 2025. Marine heatwave events (red lines) and marine coldspell events (blue lines) contrasting two competing methodologies have been overlaid. The use of a static baseline when identifying extreme events (left) leads to an increased frequency and duration of MHW events. The removal of long-term warming (right) reveals events that depart from that long-term trend, highlighting quick swings in SSTs.
Figure 4. Heat map of daily SST anomalies from a 1991 – 2020 climatological baseline from the beginning of 1982 through February 2025. Marine heatwave events (red lines) and marine coldspell events (blue lines) contrasting two competing methodologies have been overlaid. The use of a static baseline when identifying extreme events (left) leads to an increased frequency and duration of MHW events. The removal of long-term warming (right) reveals events that depart from that long-term trend, highlighting quick swings in SSTs.

Spatial Distribution of Seasonal Anomalies

When viewed spatially, winter 2024 – 25 SST anomalies show a fairly even distribution of below-average anomalies, with some concentration on the eastern half of the area and over deeper waters (Figure 5). Above-average anomalies were isolated to more shallow areas towards the Bay of Fundy or in the Western Gulf of Maine. During the winter season, a large mass of below-average SSTs was located to the south of the Gulf of Maine region off the continental shelf.

Figure 5. Map of average SST anomalies for each grid cell in the satellite record for winter 2024 – 25. 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 winter 2024 – 25. 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 winter 2024 – 25 are shown spatially in Figure 6. During December (left panel), above-average SSTs were located towards the western side of the Gulf of Maine and to the south of Cape Cod. Below-average SSTs were concentrated to the east towards the Northeast channel and Nova Scotia. The distribution of SST anomalies was similar in January (middle panel) and February (right panel), with a below-average off-shelf cold water mass appearing to move south over this period.

Figure 6. This series of maps shows the monthly average SST anomaly for December 2024, January 2025, and February 2025. 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 December 2024, January 2025, and February 2025. 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. 2025. Gulf of Maine Warming Update: Winter 2024-25 https://gmri.org/stories/gulf-of-maine-warming-update-winter-202425.

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