Record Warmth

For the 13th consecutive year, we in the state climate office have evaluated the myriad daily, monthly, and annual observations gathered across New Jersey during the course of the year to choose what we feel were the most significant and impactful 10 weather and climate events of 2021. More about each event can be found in the monthly narratives and the special Post-tropical Cyclone Ida report posted on our website. You might be tempted to rearrange the rankings, particularly as some of the events on the list may have affected you more than others ranked higher. Or perhaps you best recall one that didn't make the list. That's the enjoyment and frustration of lists! Unless stated otherwise, statewide values are based on an average of several dozen stations. The period of record for monthly, seasonal, and annual departures is 1991–2020; while for extremes and rankings it is from 1895–present. Observations are mainly drawn from National Weather Service Cooperative Observing Program stations, Rutgers NJ Weather Network stations, and NJ Community Collaborative Rain, Hail, and Snow Network locations.

August joined the chorus of much warmer-than-normal months experienced throughout most of 2020 to date across the Garden State. Six of the eight months have ranked among the top 10 warmest for the 126 years beginning in 1895. Only April and May are outliers and, in fact, each of them had below-average temperatures. With a mean of 75.5°, August tied with 2001 and 1955 as the 6th warmest. This is 2.5° above the 1981–2010 mean. Eleven of the warmest 17 Augusts have occurred since 2001. The mean maximum of 84.8° tied for 19th warmest at 1.5° above normal, while the mean minimum of 66.1° was 3.4° above normal and ranked 4th warmest.

Statewide precipitation averaged 6.04”. This is 1.94” above normal and ranks as the 26th wettest August on record. Above-average totals occurred in northern (6.02”), southern (6.10”), and coastal (5.50”) climate divisions. The southern division (Mercer-Middlesex-Monmouth counties and south, except a narrow coastal division) saw a range from the driest area in Monmouth and parts of Mercer counties and a very wet area in Salem and Gloucester counties.

Following on the heels of the 8th mildest January on record, February 2020 entered the books as the 3rd mildest since records began in 1895. The 39.2° average was 5.7° above the 1981–2010 mean. The northern climate division of the state averaged 36.2° (+5.2°; 6th mildest), the south was 41.0° (+6.1°; 3rd mildest), and the coastal division was 41.2° (+5.7°; 3rd mildest). Average minimum temperatures ranked 2nd mildest for the state, while average maximums ranked 8th mildest. To place February 2020 in some perspective, it was just 1.6° below the 1981–2010 March average of 40.8° and only 0.2° below the longer 1895–2019 March average. It was close to the long-term (1981–2010) average February temperatures in Washington, DC, Paducah, KY, and Bristol, TN.

February precipitation (rain and melted snow) came in very close to the 1981–2010 average at 2.82”. This is just 0.02” above average and ranks as the 62nd driest (and 65th wettest) of the past 126 years. Divisional totals ranged from 2.48” (-0.34”, 49th driest) in the north, 2.99” (+0.21”, 60th wettest) in the south, and 3.37” (+0.48”, 51st wettest) at the coast.

So often over the past roughly year and a half, I have been writing about statewide monthly temperatures being among the warmest on record. In fact, February, May, August, and September 2018, as well as April 2019, have ranked as 2nd, 4th, 2nd, 3rd, and 4th warmest, respectively, since statewide averages began being generated in 1895. Throughout this century, this has so often been the case that, seemingly, it is almost expected each month. Not necessarily a top 5 ranking, but often in the top 20.

This got me wondering whether I was exaggerating the warmth since 2000. Thus an evaluation of rankings was performed for each month and for the year as a whole. This included generating counts of the warmest top 10 and top 20 warmest months since 1895 that have occurred from January 2000 through April 2019.

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.