August 2025 Summary – Sunniest on Record

Enhanced GOES-East visible imagery of Hurricane Erin passing the U.S. East coast on the afternoon of 21 August 2025. The color enhancement emphasizes the cloud phase and distinguishes ice clouds (yellow-orange), liquid clouds (light blue-green), land areas (deep blue), and ocean (black). Imagery courtesy of the College of DuPage (weather.cod.edu).

Blue Hill Observatory August 2025 Summary: 

August 2025 was cooler and drier than average with much above average sunshine. The approximated 24-hour mean temperature for the month of 68.5 deg F was 0.2 degrees warmer than the 1891-2020 130-year average for August, and it was 1.8 degrees cooler than the 1991-2020 30-year average. The average maximum temperature of 79.5 deg F was 0.7 degrees cooler than the 30-year normal, and the average minimum temperature of 59.3 deg F was 3.3 degrees cooler than the 30-year normal, which was the coolest average minimum temperature in August since 1987. The warmest period of the month was the second week, which included five consecutive days with a high temperature of 88F or higher. The highest temperature for the month was 94F on the 11th, and the lowest temperature was 51F on the 20th during a cool period of onshore winds prior to the passage of Hurricane Erin far offshore on the 21st. August mean water vapor pressure, which is an absolute measure of water vapor in the air, was 16.8 mb, which corresponded to a mean dew point of about 59F. This amount was below the long-term mean water vapor pressure for August of 18.2 mb, which equals a mean dew point of about 61F, and it was the lowest for the month since 1987. The total precipitation was 1.88 inches, which was 2.03 inches less than the 30-year normal. The greatest amount in 24 hours was 0.68 inches, which occurred during a gusty thunderstorm on the 14th. There were two thunderstorm days during the month, which was two fewer than average, and the total for the year through August increased to 18, which is close to average. The highest sea-level pressure during August was 30.52 inches on the 6th, which tied as the third highest on record for the month. The lowest sea-level pressure was 29.77 inches on the 25th, which was also relatively high for August. The mean wind speed was 9.5 mph, which tied as the second lowest on record for the month, and the prevailing wind direction was from the south-southwest. The highest wind gust was 41 mph from the northeast on the 17th. Hurricane Erin passed far out over the ocean and brought a wind gust to 36 mph from the east-northeast on the 21st. August sunshine was well above average with 305.1 hours of bright sunshine, or 74 percent of possible, which was fifteen percent more than the long-term average for the month. August ranked as the sunniest on record at Blue Hill.

BHO Highest August Sea-Level Pressure, inches (1885-2025):

1) 30.60 on 31 August 2002
2) 30.55 on 25 August 1991
3) 30.52 on 22 August 1957
   30.52 on 6 August 2025
5) 30.49 on 24 August 1967
6) 30.48 on 23 August 1954
7) 30.47 on 19 August 1918
8) 30.45 on 17 August 1942

BHO Lowest August Mean Wind Speed, mph (1885-2025):

1) 9.2 in 2024
2) 9.5 in 1996
   9.5 in 2008
   9.5 in 2021
   9.5 in 2025
6) 9.8 in 2019
7) 10.0 in 1899
   10.0 in 2009
   10.0 in 2022

BHO Highest August Bright Sunshine, hours (1886-2025):

1) 305.1 in 2025 [74%]   
2) 303.7 in 1971 [74%]   
3) 303.2 in 2015 [73%]   
4) 303.0 in 1969 [73%]   
5) 298.1 in 1932 [72%]   
6) 296.7 in 1970 [72%]   
7) 296.6 in 1995 [72%]   

Mike Iacono
Chief Scientist
Blue Hill Observatory