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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.