Summer 2023 Summary – Seventh Wettest on Record

Blue Hill Observatory Summer (June-August) 2023 Summary: 

Summer 2023 was much wetter, and less sunny than average. The approximated 24-hour mean temperature for the season of 68.6 deg F was 1.0 degrees warmer than the 1891-2020 130-year average for summer, and it was 0.6 degrees cooler than the 1991-2020 30-year average. It was the coolest summer since a mean of 66.5 deg F was observed in summer 2009. The average maximum temperature of 77.8 deg F was 1.3 degrees cooler than the 30-year normal, and the average minimum temperature of 61.2 deg F was 0.1 degrees cooler than the 30-year normal. The season was generally very wet with a total rainfall of 19.70 inches, which was 7.69 inches more than the 30-year normal. Summer 2023 was the seventh wettest on record, and it was the wettest summer since 2006. The largest single rainfall event was observed on July 16th, which brought 2.56 inches of precipitation in less than 24 hours. The wettest month was July with 9.59 inches. Thunderstorms were observed on 20 days during summer, which was seven more than average, and ten of them occurred in July. One of those thunderstorms dropped 1.01 inches of heavy rain in a single hour on July 21st. The mean wind speed for summer was 9.5 mph, which was the lowest on record, and the prevailing wind direction was from the south-southwest. The highest wind gust was 61 mph from the west-northwest during heavy rain and thunder on July 27th. Summer bright sunshine was below average with 685.1 hours, or 53 percent of possible, which was four percent less than the long-term average for the season.

BHO Highest Summer (June-August) Precipitation, inches (1886-2023):

1) 25.22 in 1998
2) 24.61 in 1955
3) 24.09 in 1938
4) 21.56 in 2006
5) 21.02 in 1922
6) 20.23 in 1982
7) 19.70 in 2023
8) 19.68 in 2021
9) 18.71 in 1989
10) 17.92 in 2013

BHO Lowest Summer (June-August) Mean Wind Speed, mph (1885-2023):

1) 9.5 in 2023
2) 10.0 in 2019
   10.0 in 2021
4) 10.1 in 2020
5) 10.2 in 2012
6) 10.3 in 2008
   10.3 in 2009

Mike Iacono
Chief Scientist
Blue Hill Observatory