On May 17, 2025, the tranquil waters of Eyjafjörður, near Akureyri, provided a stunning backdrop to an extraordinary climatic event. With over a century of temperature records in Akureyri, the first 22 days of May this year boasted an astounding average of 10.9°C, setting a remarkable milestone for this period. (Photo: IMO/Haukur Haraldsson)
- For ten consecutive days, temperatures soared to or above 20°C at numerous weather stations across the country.
- Numerous temperature records for May were shattered throughout Iceland.
- A new national record of 26.6°C was recorded at Egilsstaðir Airport on May 15th.
From May 13 to 22, 2025, an unusually intense heatwave swept across Iceland, driven by a persistent high-pressure system lingering near the Faroe Islands. This atmospheric phenomenon gradually shifted its focus over Iceland, funneling warm air from the south and southeast into the region for an extended period. While similar conditions have occurred before, this heatwave stood out not only for its early arrival but also for its remarkable duration and the widespread high temperatures experienced.
Iceland basked in unseasonably warm and sunny weather during this spell, with temperatures soaring far above the average for May. The northeastern and eastern highlands recorded anomalies of over 10°C, while the southern and southeastern coasts saw increases of about 3°C or more.
Figure 1: Temperature anomalies (°C) recorded at automatic weather stations from May 13 to 22, 2025, are based on the expected daily temperatures calculated from the previous decade (2015 to 2024).
Traditionally, Iceland’s chilly May months often see temperatures that fail to cross the 20°C threshold. However, in recent years, this milestone has been reached for an average of just 2-3 days each May. This year, temperatures surpassed 20°C for ten consecutive days from May 13 to 22, along with an additional day of warmth on May 7, bringing the total to an impressive 11 days.
The peak temperatures occurred during the weekend of May 17-18, when nearly half of all weather stations in the country registered temperatures above 20°C. Notably, the national average temperature also reached its zenith during this time.
The first three weeks of May 2025 were exceptionally warm, with only two days registering slightly below-average temperatures when compared to a ten-year historical benchmark. For most weather stations, this May has already shattered previous average records, including historic locations like Stykkishólmur (reliable data since 1846), Reykjavík (since 1881), and others. Notably, Akureyri’s average temperature for the first 22 days reached 10.9°C, the highest ever recorded for this time frame. Similarly, Grímsstaðir á Fjöllum observed an average of just under 10°C, marking a new high over 119 years of continuous measurement.
Figure 2: A bar chart reflects the percentage of weather stations recording temperatures of 20°C or higher from May 1 to 22, 2025. On May 17 and 18, approximately 50% of all stations documented such temperatures, with the highest reading—a remarkable 26.6°C—registered at Egilsstaðir Airport on May 15.
Figure 3: A comparison of the national daily average temperature from May 1 to 22, 2025, against the past decade (2015 to 2024). Overall, these days have proven significantly warmer, with only May 9 and 10 falling slightly below the average.
Numerous May Records Broken
Remarkably, new temperature records for May were established at 94% of automatic weather stations that have been operational for over 20 years. The apex was the 26.6°C reached at Egilsstaðir Airport on May 15, eclipsing the prior record of 25.6°C set in Vopnafjörður on May 26, 1992.
Following this record-setting day, temperatures were surpassed again on several occasions:
- Egilsstaðir Airport registered 26.4°C on May 17,
- Végeirsstaðir in Fnjóskadalur saw 26.0°C on May 17,
- Húsafell recorded 25.7°C on May 18.
Figure 4 depicts automatic weather stations where new May maximum temperatures were recorded, focusing on those with at least 20 years of historical data. Remarkably, 83 out of 88 such stations set new May records, primarily on May 17 and 18, although peak temperatures varied slightly by region.
The longevity of manned weather stations lends them a historical perspective. Among those, the highest recorded May temperatures included:
- Stykkishólmur: 20.5°C (May 17, 174 years of data),
- Grímsstaðir á Fjöllir: 24.0°C (May 15, 119 years of data),
- Litla-Ávík: 23.3°C (May 17, 31 years of data).
Reykjavík also experienced its second-highest May temperature ever at 20.3°C, surpassing the previous record set in 1960. Similarly, Akureyri recorded 24.2°C on May 17, near its record of 24.6°C set in 1980.
Figure 4 highlights the locations of automatic stations that set new temperature records during the May 2025 heatwave, with color coding indicating the days on which those records were achieved.
Historical Heatwaves
Heatwaves are not entirely unprecedented in Iceland, with certain spells witnessing significantly elevated temperatures for several consecutive days. However, the current heatwave (May 13-22, 2025) stands as the most intense ever documented for the month of May. The last comparable event occurred in 1987, under remarkably similar atmospheric conditions.
In more recent history, significant heatwaves emerged around late July and early August of 2008 and in August 2004. During these times, numerous temperature records were also shattered, with values reaching 20°C over several consecutive days. It’s worth noting that these earlier heatwaves registered even higher temperatures, occurring during the peak of summer rather than spring.
Temperatures during the summer of 2021 were noticeably elevated, although that heat was largely confined to the northeastern and eastern regions of Iceland. Further noteworthy heat events occurred in July 1976 and 1991. A notable heatwave in June 1939 even saw the mercury rise to an astonishing 30.5°C at Teigarhorn on June 22—the highest temperature ever recorded in Iceland.
