For the fourth consecutive year, summer weather stubbornly hung on well into September across the Garden State. The statewide average temperature of 70.4° was 4.6° above the 1981–2010 mean, and ranks as the third warmest since records commenced in 1895. September 2017, now ranking 11th, sat in the top 10 for just one year before being bumped out by 2018. This September was the fifth consecutive month of above-average temperatures. The past 12 months have seen the 2nd warmest October, 4th warmest May, 1st warmest August (tied with 2016 based on updated figures), and now the 3rd warmest September. The June through September period this year averaged 73.3° (+2.5°), making it the 4th warmest on record. The top 10 such intervals have all occurred since 2005. The August–September average of 73.7° (+4.3°) was the warmest on record, followed by 2005, 2016, 2015, and 2010.
Perhaps what was most interesting about temperatures this past month was the disparity between average maximum and minimum temperature anomalies. The average maximum of 77.7° was 1.4° above average and ranked 27th warmest. However, the average minimum of 63.2° was 7.9° above average and is a whopping 2.2° milder than the previous highest September average minimum. This came about due to the excessive cloud cover and humidity throughout most of the month, which kept the days from getting too warm and, come nighttime, “trapped” much of the heat gained during the day within the lower atmosphere. Thus, unlike the past three warm Septembers (as well as 2013 and 2014), each of which had below-average precipitation, this year was anything but dry. There were frequent rainy episodes, which at times produced localized deluges and resultant flash flooding. The statewide average rainfall of 7.60” is 3.55” above the 1981–2010 average, and is tied with 1960 as the sixth wettest September since 1895. The wettest September on record remains 1999, which averaged 9.50 inches, in no small part due to Tropical Storm Floyd’s rains. Aside from 1999, you have to go back to 1975 to find a September with more rain than this year.