September 2020 was a touch milder than average (+0.8 degree), with close to an average amount of rain (3.94"). The month's story can be told by three eight-day periods: Sept. 3-9 was four degrees above average, Sept. 23-30 was six degrees above average, and the middle of the month (Sept. 15-22) was six degrees chillier than average, and rain-free. Nearly all of the month's nearly four inches of rain was produced by three storm systems: 0.71" on 9/3, 1.20" on 9/10 and 1.61" on 9/29-30.
The month's near average rainfall belied a 16-day streak with no measurable rain (Sept. 11-26). This was the longest dry streak since the fall of 2017. These dry conditions were largely due to a strong high pressure system that anchored itself over the Northeast for about a week. It prevented moisture from hurricane Sally and tropical storm Beta from moving into the area and brought chilly air into the region, delivering the City's earliest lows in the 40s in seven years (49° on 9/21, 48° on 9/22).
Just seven days had highs of 80° or warmer, joining ten other Septembers since 1970 with this few. The warmest reading was 85°, occurring on 9/3 and again on 9/4 (a typical September's hottest reading is around 90°). The month's average high of 75.5° was the coolest since 2009. And although the month's average temperature was a touch above average, it was the coolest September since 2013.
Finally, although highs in the 80s/90s and lows in the 70s occasionally occur in October, if 2020's final reading of 80°+ remains at 9/10, it will be one of the earliest dates on record for this occurrence. Meanwhile, the 58 lows of 70°+ is the third most after 1906 (61) and 2005 (60).
Here are previous September recaps: