September 2021 Summary – Warmer and Wetter Than Average

| October 7, 2021 | Reply

Blue Hill Observatory September 2021 Summary:

September was very warm and wetter than average. The 24-hour adjusted mean temperature for the month of 64.8 deg F was 3.3 degrees warmer than the 1891-2020 130-year average for September, and it was 1.7 degrees warmer than the 1991-2020 30-year average. The month tied with 2018 as the 11th warmest September on record. The average maximum temperature of 73.2 deg F was 2.1 degrees warmer than the 130-year mean. The average minimum temperature of 57.4 deg F was 3.7 degrees warmer than the 130-year mean, and the average minimum tied with 2002 as the tenth warmest on record. The highest temperature observed all month was 82F on the 15th, and the lowest temperature during September was 45F on the 29th. The mean water vapor pressure during the month was 17.4 mb, which reflected the high level of moisture in the air during September and was the fourth highest on record for the month. September total precipitation was 6.64 inches, which was about two and a half inches more than the 130-year average and the 1991-2020 30-year mean. Most of this rainfall occurred on the first two days of the month, when former Category 4 Hurricane Ida passed New England as a post-tropical storm bringing 4.00 inches of rain between mid-day on the 1st and sunrise on the 2nd along with a wind gust to 49 mph from the ENE early on the 2nd. The heaviest rain in this time occurred in the early morning hours of the 2nd with 0.86 inches in the hour from 1-2 AM EST and 1.57 inches in two hours from 1-3 AM EST. The 4.00 inches was also the greatest in 24 hours for the month. There were three thunderstorm days during September, which was one more than average, and the annual total through September is 24, which is two more than average. The mean wind speed for the month was 11.0 mph, and the prevailing wind direction was from the northwest. The highest wind gust was 49 mph from the ENE during the passage of Ida on the 2nd. September sunshine was below average with 191.5 hours of bright sunshine, which was 53 percent of the possible sunshine and four percent less than the 130-year mean.

BHO Warmest September Average Minimum Temperature, deg F (1885-2021):

1) 58.6 in 2018
2) 58.5 in 2015
3) 58.2 in 1961
58.2 in 1999
5) 57.9 in 2016
6) 57.8 in 2005
7) 57.6 in 2011
8) 57.5 in 1934
57.5 in 1971
10) 57.4 in 2002
57.4 in 2021

BHO Highest September Average Water Vapor Pressure, mb (1932-2021):

1) 17.9 in 1961
2) 17.6 in 2018
3) 17.5 in 2011
4) 17.4 in 2021
5) 17.3 in 2015
6) 17.2 in 1934

Mike Iacono
Chief Scientist
Blue Hill Observatory

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Category: Weather Summary Archives

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