August 2018 Summary – Second Warmest on Record

Blue Hill Observatory

August 2018 Summary:

August was generally very warm and sunny with near normal precipitation. The 24-hour adjusted mean temperature for the month of 73.4 deg F was 5.3 degrees warmer than the 120-year average for August and 4.0 degrees warmer than the 1981-2010 30-year average. This mean temperature was the second warmest on record for August behind only 74.1 deg F in 2016. The average maximum temperatures of 82.4 deg F tied for the eighth warmest on record, and the average minimum temperature of 66.3 deg F was the warmest ever observed in August. There were five ninety-degree days, which is three more than average, and the yearly total is up to 12, which is six more than average through August. The highest temperature for the month was 94F on the 29th, and the lowest temperature of 59F on the 24th, 25th, and 26th was the highest ever measured in August. There were no daily record maximum temperatures during the month, though there were three daily record high minimum temperatures including 74F on the 3rd, 73F on the 7th, and 75F on the 29th. A total of 3.94 inches of precipitation was measured, which was slightly less than the long-term 120-year average and the 30-year mean. About 30 percent of the monthly total, 1.16 inches, was the greatest amount to fall within 24 hours, though it actually fell in less than five hours during thunderstorms on the 4th. There were five thunderstorm days during August, one more than average for the month, which brought the annual total up to 16. The mean wind speed was 10.2 mph, and the prevailing direction was from the southwest. A peak gust of 35 mph from the northwest occurred on the 3rd and again from the west-northwest on the 22nd. August had average sunshine with 238.4 measured hours of bright sunshine, or 58 percent of possible, which was exactly equal to the long-term mean.

BHO Warmest August Mean Temperature (24-hour adjusted), deg F (1885-2018):

1) 74.1 in 2016
2) 73.4 in 2018
3) 72.6 in 2012
4) 72.5 in 1988
5) 72.4 in 2015

BHO Warmest August Average Maximum Temperature, deg F (1885-2018):

1) 85.1 in 2016
2) 83.2 in 2005
3) 83.1 in 1949
4) 82.6 in 2015
5) 82,5 in 1988
   82.5 in 2002
   82.5 in 2012
8) 82.4 in 1944
   82.4 in 2018

BHO Warmest August Average Minimum Temperature, deg F (1885-2018):

1) 66.3 in 2018
2) 65.0 in 2016
3) 64.9 in 2001
4) 64.6 in 2012
5) 64.4 in 2005
   64.4 in 2015

BHO Warmest August Monthly Minimum Temperature, deg F (1885-2018):

1) 59 in 2018
2) 58 in 1939
   58 in 2015
4) 57 in 1901
   57 in 2001

BHO Greatest August Water Vapor Pressure, mb (1932-2018):

1) 22.5 in 2018
2) 21.6 in 1937
3) 21.5 in 1988
4) 21.0 in 1955
   21.0 in 2009
6) 20.9 in 2003

Summer (Jun-Aug) 2018 Summary:

Summer 2018 became increasingly warmer than average during the season with slightly less rainfall than normal  The 24-hour adjusted mean temperature for June-August of 70.9 deg F was 3.6 degrees warmer than the 120-year average for Summer and 2.4 degree warmer than the 1981-2010 30-year average. Summer 2018 was the third warmest on record. The precipitation total was 10.63 inches, which was about three-quarters of an inch less than the long-term mean and about an inch and a half less than the 30-year average. The greatest rainfall in 24 hours was 1.36 inches on July 17th-18th. The 14 thunderstorm days during Summer was just one more than average. Summer sunshine was greater than average with 60 percent of the possible bright sunshine, which was three percent more than the long-term mean.

BHO Warmest Summer (Jun-Aug) Mean Temperature (24-hour adjusted), deg F (1885-2018):

1) 71.6 in 2016
2) 71.3 in 2010
3) 70.9 in 2018
4) 70.8 in 1949
5) 70.6 in 1999

Mike Iacono
Chief Scientist
Blue Hill Observatory