September is more likely than May to see 90-degree temperatures. While May experiences a 90-degree day once every three years, September sees one about every two years. The most such days in occurred in 1961, when there were eight, followed by seven in 1895, 1970 and 1983. The most consecutive years to have a 90-degree reading in September is eleven, from 1936 to 1946. (Presently we are in the midst of a six-year streak, 2012-2017.) The most consecutive years without one is six, from 1885 to 1890. Finally, three days in September have never had a reading in the 90s: 9/28, 9/29 and 9/30 (9/24 was on this list until 2017).
Only four of New York's ten warmest Septembers are among those with the most 90-degree days: 2015 (warmest September on record/six 90-degree days); 1961 (second warmest September/eight 90-degree days); 1931 (sixth warmest/five 90-degree days); and 1983 (tenth warmest/seven 90-degree days). And one of the ten years with the most 90-degree days, 1988 (32 days), reported no 90-degree days in September.
Finally, there have been four years with 90-degree readings in October - the last time was in 1941. Two of those years were back-to-back (1938 and 1939), and in both years there were no 90-degree days in September. October 1941 had two 90-degree days, including the hottest October reading on record - 94° on 10/6. In addition, there have been nine years in which there were 90-degree days in the last ten days of September, most recently in 1980.