October 2017 Summary – Warmest on Record

Blue Hill Observatory

October 2017 Summary:

October was notable for being very warm, and it was drier than normal until a significant rainstorm in the final days of the month. The 24-hour mean temperature for the month of 59.2 deg F was 8.1 degrees warmer than the 120-year average for October and nearly eight degrees warmer than the 1981-2010 30-year average. This made October the warmest on record by nearly a full degree F. The average maximum temperature for October was 68.0 deg F, which was the third warmest on record, and the average minimum temperature was 51.7 deg F, which surpassed the previous record for October by more than two degrees. The high temperature of 79F occurred on the 5th. Several daily high minimum temperature records were set including 67F on the 8th and 68F on the 9th, which surpassed the previous record for the date of 61F in 2011. This reading also established a new monthly high minimum temperature record for October, surpassing the previous record of 67F on October 13, 1990 and on October 8th, 2017.  A minimum temperature of 64F on the 24th was not only a new record for the date, surpassing 61F set in 2001, but it was also the warmest daily minimum temperature of 64F or higher so late in the season. The coldest temperature during October was 35F on the 17th, and there were only three days all month that averaged colder than the 30-year normal, the 1st, 2nd and 17th. Fifteen days were ten degrees or more warmer than normal. The monthly mean water vapor pressure (a measure of moisture in the air) of 13.2 mb was a new record for October. A total of 5.94 inches of precipitation was measured during the month, which was over an inch more than the long-term 120-year average and about two inches more than the 30-year mean. The greatest amount in 24 hours was 3.12 inches (more than half of the monthly total) during a very strong rain and wind storm on the 29th-30th. This was the first month this year without a thunderstorm day, which leaves the annual total at 17. The mean wind speed for October was 12.8 mph, and the prevailing direction was from the south. The strong rain and wind storm on the 29th-30th brought a peak gust of 73 mph from the southeast on the 30th, which surpassed the previous record wind gust for the date of 66 mph NW in 1963. The lowest sea-level pressure during this storm was 29.03 inches (983.0 mb) on the 30th, which tied for the second lowest pressure ever measured during October. The month was sunnier than average with 192.0 hours of bright sunshine, or 58 percent of possible, being observed, which was two percent more than the long-term October mean.

BHO Warmest October 24-hour Corrected Mean Temperature, deg F (1885-2017):

1) 59.2 in 2017
2) 58.4 in 1947
3) 56.9 in 2007
4) 56.6 in 1971
5) 56.5 in 1963

BHO Warmest October Average Maximum Temperature, deg F (1885-2017):

1) 70.1 in 1947
2) 68.5 in 1963
3) 68.0 in 2017
4) 66.4 in 1946
5) 66.1 in 2007

BHO Warmest October Average Minimum Temperature, deg F (1885-2017):

1) 51.7 in 2017
2) 49.5 in 2007
3) 49.2 in 1971
4) 49.1 in 1947
5) 48.2 in 1913

BHO Highest October Daily Minimum Temperature, deg F (1885-2017):

1) 68 on October 9th, 2017
2) 67 on October 13th, 1990
   67 on October 8th, 2017
4) 66 on October 18th, 1908

BHO Highest October Mean Water Vapor Pressure, mb (1932-2017):

1) 13.2 in 2017
2) 12.7 in 2007
3) 12.4 in 1971
4) 11.9 in 1990
   11.9 in 2012

BHO Lowest October Sea-Level Pressure, mb (1885-2017):

1) 28.95 in 1925
2) 29.03 in 1926
   29.03 in 2006
   29.03 in 2017
5) 29.04 in 1927
6) 29.08 in 1972
   29.08 in 2003



Mike Iacono
Chief Scientist
Blue Hill Observatory