Summer 2025 Summary – Warmer and Drier Than Average

Blue Hill Observatory Summer (Jun-Aug) 2025 Summary: 

Summer 2025 temperature was much above average, and there was less precipitation and more sunshine than expected. The approximated 24-hour mean temperature for summer of 70.2 deg F was 2.7 degrees warmer than the 1891-2020 130-year average for the season, and it was 1.0 degrees warmer than the 1991-2020 30-year average. Summer 2025 tied as the eleventh warmest on record. The average maximum temperature of 80.8 deg F was 1.7 degrees warmer than the 30-year normal, and it was the tenth warmest on record. The average minimum temperature of 61.4 deg F was 0.1 degrees warmer than the 30-year normal, which was the fifteenth warmest on record. There was one four-day heat wave during Summer 2025, on June 22nd-25th, and there were 18 ninety-degree days, which was twelve more than average. Summer 2025 was generally warm during June and July, while much of August was cooler than average. The warmest temperature was 99F on June 24th, which matched the highest temperature ever measured at Blue Hill during June and surpassed the previous record for the date of 91F set in 1914, 1976, and 2013. The lowest temperature was 47F on June 1st. The average water vapor pressure was 18.8 mb, which corresponded to a mean dew point of 62F. This value was higher than the long-term average vapor pressure for summer of 17.6 mb, which corresponds to an average dew point of 60F. The season was drier than average, and the total precipitation was 9.59 inches, which was 2.42 inches less than the 30-year normal. Sixty-five percent of the summer rainfall fell during the wet month, July, while June and August were much drier than average. The greatest amount in 24 hours was 3.85 inches on July 10th, which was forty percent of the seasonal rainfall and was caused by an exceptionally heavy band of rain including a thunderstorm that morning. On that day, 1.35 inches of rain was recorded in a single hour. The minimal effects of distant Hurricane Erin, which passed far offshore on August 21st, brought a trace of precipitation and a peak wind gust to 36 mph from the east-northeast. There were eleven thunderstorm days during summer, which was three fewer than average for the season. The mean wind speed was 9.8 mph, which was the second lowest on record for summer, and the prevailing wind direction was from the south-southwest. The highest wind gust was 52 mph from the west-northwest during the arrival of some briefly cooler air on June 20th. Summer sunshine was above average with 825.8 total hours of bright sunshine, or 64 percent of possible, which was seven percent more than the long-term average for the season.

BHO Warmest Summer (Jun-Aug) Average Maximum Temperature, deg F (1885-2025):

1) 83.0 in 1949
2) 82.9 in 2022
3) 82.4 in 2016
4) 82.1 in 2010
5) 81.5 in 1952
6) 81.3 in 2020
7) 81.0 in 2024
8) 80.9 in 1999
   80.9 in 2005
10) 80.8 in 2025

BHO Lowest Summer (Jun-Aug) Mean Wind Speed, mph (1885-2025):

1) 9.5 in 2023
2) 9.8 in 2025
3) 10.0 in 2019
   10.0 in 2021
   10.0 in 2024
6) 10.1 in 2020
7) 10.2 in 2012
8) 10.3 in 2008
   10.3 in 2009

Mike Iacono
Chief Scientist
Blue Hill Observatory