July 2023 Summary – Fifth Wettest on Record

Blue Hill Observatory July 2023 Summary: 

July 2023 was much warmer and much wetter than average with several days of heavy rain. The approximated 24-hour mean temperature for the month of 73.5 deg F was 3.5 degrees warmer than the 1891-2020 130-year average for July, and it was 1.8 degrees warmer than the 1991-2020 30-year average. The month tied with 1949 as the 12th warmest July on record. The average maximum temperature of 82.7 deg F was 1.0 degrees warmer than the 30-year normal, and the average minimum temperature of 65.7 deg F was 1.9 degrees warmer than the 30-year normal and tied for the fourth warmest on record. The month was consistently warm with only eight days cooler than average, but there were few extremes with only two days above 90F. The highest temperature was 92F on the 6th, and the coolest temperature was 56F on the 30th, one of only two days during July with low temperatures below 60F. The month was also notable for generally high humidity and dew points. The average water vapor pressure, which directly represents the amount of moisture in the air, was 22.9 mb, which was the second highest on record for July and for any month of the year. July precipitation was excessive with a total of 9.59 inches, which was 6.12 inches more than the 30-year normal, and July was the fifth wettest on record. Much of the monthly rainfall, 6.61 inches, fell on just four days, the 16th, 21st, 25th, and 29th. The greatest rainfall within 24 hours was 2.56 inches on the 16th. A total of 5.88 inches fell as mostly heavy rainfall within 11 individual hours during July, including 1.01 inches within a single hour during a thunderstorm on the 21st. Thunderstorms were observed on ten days during the month, which is five more than average, but this number is well below the July record of 15 in 1988. The total thunderstorm days for the year has climbed to 20, which is also five more than average through July. The mean wind speed was 9.3 mph, which was a new record low monthly mean wind speed for July and the second lowest for any month of the year. The prevailing wind direction was from the south-southwest. The highest wind gust was 61 mph from the west-northwest on the 27th during a thunderstorm with frequent lightning and a period of heavy rain. Despite the rainfall, July bright sunshine was near average with 255.2 hours, or 57 percent of possible, which was one percent less than the long-term average for the month.

BHO Highest July Average Minimum Temperature, deg F (1885-2023):

1) 66.9 in 2013
2) 66.0 in 2020 
3) 65.9 in 2010
4) 65.7 in 2022
   65.7 in 2023
6) 65.6 in 1994
   65.6 in 2019
8) 65.3 in 2006

BHO Highest Monthly Average Vapor Pressure, mb (1932-2023):

1) 23.5 in July 2013
2) 22.9 in July 2023
3) 22.5 in July 1994
22.5 in August 2018
5) 21.9 in August 2021
6) 21.8 in July 2020
7) 21.7 in July 2006
8) 21.6 in August 1937
9) 21.5 in August 1988

BHO Highest July Average Vapor Pressure, mb (1932-2023):

1) 23.5 in 2013
2) 22.9 in 2023
3) 22.5 in 1994
4) 21.8 in 2020
5) 21.7 in 2006
6) 21.3 in 1988
7) 21.2 in 1955
21.2 in 1975

BHO Highest July Precipitation, inches (1886-2023):

1) 11.67 in 1938
2) 11.59 in 2021
3) 10.66 in 1988
4) 10.43 in 1921
5) 9.59 in 2023
6) 9.52 in 1915
7) 8.47 in 1889
8) 7.62 in 2009

BHO Lowest Monthly Mean Wind Speed, mph (1885-2023):

1) 9.2 in June 2023
2) 9.3 in July 2023
3) 9.5 in August 1996
   9.5 in August 2008
   9.5 in August 2021
6) 9.6 in July 2019
7) 9.7 in July 2021

BHO Lowest July Mean Wind Speed, mph (1885-2023):

1) 9.3 in 2023
2) 9.6 in 2019
3) 9.7 in 2021
4) 9.8 in 2012
   9.8 in 2020

Mike Iacono
Chief Scientist
Blue Hill Observatory