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October 2017

Recap of September 2017 Weather: The Great Rebound




After experiencing the coolest start to the month since 1975 (thru 9/12), a complete turnaround occurred, with temperatures nine degrees above average during a streak of sixteen unseasonably warm days (thru 9/28).  This included a record high of 91° on 9/25, the first 90-degree reading since 8/1, and the latest temperature in the 90s since 1970.  As a result of this rebound the month ended up being 2.5 degrees above average, the fourth year in a row in which September had warmer than average temperatures.  (The final two days of the month reverted back to the cool conditions experienced at the beginning of September, but by then such temperatures were close to average.)  Other highlights:


  • With just 2.00" of rain, September was the driest month since August of last year (when 1.97" was measured), and the sixth driest September since 1980.  Much of the rain fell in a 12-hour period on the night of 9/2 into the early morning hours of 9/3 (1.27").  No rain fell in the last 11 days of the month, tying an equally long streak in February as the longest dry spell of the year.  (This dry spell continued into the first week of October.)  The month's last rainfall, 0.22" on 9/19, was produced by Hurricane Jose, which New York was on the western edge of.
  • September's average temperature was 3.5 degrees cooler than August's, the closest September has been to August since 1961 (the average difference is 7.2 degrees). 
  • This was the sixth September in a row to have at least one high in the 90s, the longest such streak since one of seven years from 1940 to 1946 (which would be tied in Sept. 2018).
  • The last day of the month and 9/2 had the month's coolest reading, 54°.  However, while this reading was eleven degrees below average on 9/2, it was just one degree below average on 9/30.
  • Although it fell during the cool first part of September, Labor Day was sunny and pleasant with a seasonable high/low of 80/61.
  • The average high/low of 74/59 in the first twelve days of September was followed by a warm 82/69 from Sept. 13-28.
  • Embedded in the sixteen-day streak of unseasonably warm temperatures were five days in a row (Sept 23-27) with mean temperatures 10 degrees or more above average, the longest such streak in 20 months (October 2017 would have a streak that lasted seven days).  Temperatures were 14 degrees above average during these five days, with an average high/low of 87/69.
  • This was the third September in a row with an average temperature of 70.0 degrees or warmer, making this the longest such streak on record.


Sept 2017


Here are links to September summaries of the previous three years:

September 2016

September 2015

September 2014