Gulf of Maine Warming Update: Spring 2025

Reports | Jul 8, 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 spring 2025 Gulf of Maine warming update.

2025 Spring Warming update

Spring 2025 Highlights

For this seasonal report we present an analysis of sea surface temperature (SST) for spring 2025, defined as the period extending from March 1, 2025 through May 31, 2025.

Springtime in the Gulf of Maine is when SSTs dip to their annual lows (typically in March), followed soon-after by a climb in temperature and the pronounced spring peak in phytoplankton productivity. Vertical mixing over the winter replenishes critical nutrients to the surface waters which, together with longer durations of sunlight, fuel the spring phytoplankton bloom. This is a very active time of year for marine species looking to take advantage of the seasonal bounty of plankton.

This year, the average spring SST for the Gulf of Maine was 43.13°F. This seasonal average temperature was 0.29°F above the 1991 – 2020 climatological reference period (CRP) spring average of 42.84°F, ranking as the 17th warmest (28th coldest) spring on record (extending 40+ years since satellite observations began in the fall of 1981).

Weekly Temperatures

Table 1 highlights how the SST for each week this spring compares to the 1991 – 2020 CRP for the area shown in Figure 7.

The observed SST, long-term average SST, and SST anomalies (i.e., departures from the long-term average SST) are shown.

Weekly SST anomalies this spring ranged from as low as -1.87°F in early March, to as high as +2.47°F during mid-May.

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 spring 2025. The first row is just one day, as a result of how the weeks are split up.
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 spring 2025. The first row is just one day, as a result of how the weeks are split up.

Monthly Statistics

Table 2 shows the average monthly SSTs for the spring of 2025. The SST in March was slightly below the 1991 – 2020 CRP, with the SST anomalies trending warmer during April and remaining positive for much of May. May SST deviated most from the long-term climatological average, with an average SST anomaly of 1.09°F.

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 spring 2025.
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 spring 2025.

How Does this Spring Compare to the Past?

2025 was the 17th warmest (28th coldest) spring season observed in the Gulf of Maine during the 42 years we have satellite data to analyze, a departure from spring seasons in the past three years, which experienced much warmer conditions.

Figure 1. A ranking of the 20 warmest spring seasons for the Gulf of Maine in the satellite record (1982 – 2025). 2025 was the 17th warmest spring on record.
Figure 1. A ranking of the 20 warmest spring seasons for the Gulf of Maine in the satellite record (1982 – 2025). 2025 was the 17th warmest spring on record.

Seasonal Trends and Long-Term Global Context

The Gulf of Maine is an area of particular interest to the scientific community due to the remarkable rate of warming it has experienced in the last decade.

Figure 3 illustrates the average spring temperature anomaly for each year in the Gulf of Maine, overlaid with long-term SST anomaly trends for the Gulf of Maine (orange) and global oceans (blue).

The spring rate of warming for the Gulf of Maine (0.53°F per decade) is just-under 2x as fast as the spring warming rate globally (0.29°F per decade).

Figure 2. Average annual spring SST anomalies in the Gulf of Maine from 1982 through 2025 (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 spring SST anomalies in the Gulf of Maine from 1982 through 2025 (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) 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 exceeding the threshold do not constitute a break in a single MHW/MCS event.

Using this broadly accepted definition, the Gulf of Maine has experienced no MHW conditions this spring. There was a brief period of temperatures above the 90th percentile threshold during May, but conditions did not persist for five days.

Figure 3. Time series of SSTs in the Gulf of Maine extending from January 1, 2025 through May 31, 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.
Figure 3. Time series of SSTs in the Gulf of Maine extending from January 1, 2025 through May 31, 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.

Heatmap of Temperature Anomalies and Extreme Events

Using our standard definition for extreme events, spring 2025 has continued to be mild with respect to MHW/MCS conditions, with no events occurring since the brief winter coldspell (Figure 4).

Elevated SST conditions have been more frequent and persistent after 2010 and throughout the early 2020s in the Gulf of Maine. During this period, the frequency, duration, and intensity of marine heatwaves have been more pronounced. Marine coldspells were common in earlier decades but have become rare, with only two occurring in the last 15 years.

Figure 4. Heat map of daily SST anomalies from the beginning of 1982 through May 2025. Periods where SSTs meet or exceed the criteria for extreme event conditions (heatwaves and coldspells) have been overlaid with a horizontal bar (red for heatwaves, blue for coldspells) for the event’s duration.
Figure 4. Heat map of daily SST anomalies from the beginning of 1982 through May 2025. Periods where SSTs meet or exceed the criteria for extreme event conditions (heatwaves and coldspells) have been overlaid with a horizontal bar (red for heatwaves, blue for coldspells) for the event’s duration.

Spatial Distribution of Seasonal Anomalies

When viewed spatially, much of the Gulf of Maine region and the adjacent on-shelf areas experienced neutral SSTs during spring of 2025 (Figure 5). Conditions were slightly cooler further offshore near the Northeast Channel, and warmest in shallow coastal areas around Cape Cod. Off-shelf water masses showed stronger SST anomalies.

Figure 5. Map of average SST anomalies for each grid cell in the satellite record for spring 2025. 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 spring 2025. 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 Spring 2025 are shown spatially in Figure 6. During March, mild above-average SSTs occupied the interior of the continental shelf, with below-average anomalies located along the shelf break, within the Northeast Channel and Downeast Maine. During April, the below-average conditions were more widely distributed in the Gulf of Maine. By May there were signs of above-average conditions on the edge of Georges Bank, but enduring slightly below-average SSTs over most of the Gulf of Maine.

Figure 6. This series of maps shows the monthly average SST anomaly for March, April, and May 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 March, April, and May 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.

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 outlined with the dashed line below. For this body of work we use a rectangular bounding box with longitudinal bounds from -70.875 W to -65.375 W, and latitudinal bounds of: 40.375 N to 45.125 N. This area is consistent with previous seasonal and annual SST reports that scientists at GMRI have produced.

Figure 7. Spatial domain used for Gulf of Maine SST analyses. For this body of work we use longitudinal bounds of: -70.875 W to -65.375 W, and latitudinal bounds of: 40.375 N to 45.125 N. Depth contours are colored at 100 m intervals up to 600 m; deeper blues indicate deeper off-shelf water depths.
Figure 7. Spatial domain used for Gulf of Maine SST analyses. For this body of work we use longitudinal bounds of: -70.875 W to -65.375 W, and latitudinal bounds of: 40.375 N to 45.125 N. Depth contours are colored at 100 m intervals up to 600 m; deeper blues indicate deeper off-shelf water depths.

Citing This Work

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

Gulf of Maine Research Institute. 2025. Gulf of Maine Warming Update: Spring 2025 https://gmri.org/stories/gulf-of-maine-warming-update-spring-2025

Note About the Data: The figures in this report are created using remotely-sensed satellite data as part of publicly funded research efforts. Satellite 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.

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