September 2019 may or may not stand alone as the hottest September ever in Oneida — that’s to be determined — but it will almost certainly stand among a select group of Septembers through the years that have been miserably hot.

When you talk about September 2019, in terms of just how hot it has been, you have to talk about the Septembers of 2016, 2002, 1998, and 1980. Throw in 2019, and you have the five most miserable summers in Oneida since records-keeping began in the mid 20th century.

The official high temperature in Oneida today (September 17) was 92 degrees. That marks the seventh day this month that the high temperature has been 90 or hotter. It also marks the fifth day this month that has featured record-setting daily temperatures. 

The record for most 90-plus-degree days in September is nine, set in 1998. There’s plenty of time for September 2019 to make a run at that record, but that will probably require the heat ridge to rebuild later in the month. After tomorrow, temperatures will cool off a bit due to a cold front. It’s going to remain hot, relative to normal for this time of year, but getting to 90 degrees gets increasingly difficult as the region moves deeper into the fall season and the sun position continues to slide lower in the sky.

Run at a record

If the month ended today, Oneida’s average temperature for September would be 72.8 degrees. That’s exactly four degrees above average for the month, and it would go down as the second-warmest month of September on record, behind September 2018, which featured an average temperature of 73.4 degrees.

Since climatology alone suggests that the current average of 72.8 degrees will almost certainly drop over the last two weeks of September, even if warmer-than-average temperatures continue, it’s going to take something currently unexpected for September 2019 to break the record as the warmest-ever September in Oneida — and it’s quite possible that it might not even go down as one of the Top 5 warmest Septembers, though it’s unlikely that it’ll fall completely off that list.

But average temperatures are just one part of the equation, as we’ll examine more closely in a moment.

Hot for different reasons

At first glance, it’s quite noteworthy that the two warmest Septembers on record in Oneida, at least in this point, occurred in back-to-back years, 2018 and 2019. But a closer look reveals two Septembers that were warm for completely different reasons.

While September 2018 was the warmest-ever September, with an average temperature of 73.4 degrees, its average afternoon high temperature of 82.6 degrees — while certainly above average — wasn’t anywhere close to the top of the list. It currently ranks as the ninth-hottest September in terms of daily high temperatures, and is likely to fall to 10th once September 2019 is in the books.

The culprit for making September 2018 so warm was nocturnal temperatures. The average nighttime low temperature of 64.1 degrees last September was a record — and it wasn’t even close. The next closest September, in terms of warmest nights, was back in 1970, when the temp dropped only to 59.5 degrees each night.

By contrast, September 2019 — while very hot by day — has been close to normal by night. As of September 17, the average daily low temperature in Oneida has been 57.1 degrees, less than one degree above average. 

Why? One word: moisture. Those who remember the very wet stretch of weather East Tennessee recently experienced will recall that the wet stretch began in September 2018. We received a whopping 12.2 inches of rain last September, smashing the previous record for the wettest September, 2003, which featured 8.89 inches of rain. Compare that to this year, which has featured only four-hundredths of an inch of rain in Oneida thus far.

Lots of cloudy days block out enough of the sun’s rays to hold down diurnal temperatures, but cloudy nights prevent radiational cooling and keep nighttime temperatures warmer.

Painfully hot

So while 2018 featured the warmest September on record in Oneida, it didn’t feel nearly as hot last year as it has felt this year, because the warmest temps — relative to normal — were occurring during the night, when most of us were asleep in our beds. The daytime temperature only reached 90 degrees twice in September 2018, compared to seven times (and counting) in September 2019.

While September 2019 almost certainly won’t break September 2018’s record as the warmest-ever September in Oneida, it could very well go down as the hottest September in terms of daytime high temperatures. As of September 17, the average daytime high temperature in Oneida for the month has been 88.5 degrees. The hottest September on record in this regard is 1998, which featured an average daytime high of 86.7 degrees. Running second was 2005, with an average daytime high of 85.0 degrees.

September 1998 was miserably hot, with the temperature topping out at 94 degrees on September 14. The hot weather lasted throughout the month, hitting 90 degrees as late as September 28, just three days before October began. The first day of October featured a high temperature of 86 degrees, and temperatures were in the mid 80s a week into the month. October 1998 was much warmer than normal, and the warmth continued into November, as well.

The 1998 heat wave wasn’t synoptically identical to 2019, but one thing the two Septembers did have in common: they were abnormally dry. Only four-tenths of an inch of rain was recorded in Oneida in September 1998.

September by September

Here’s a brief look at the other Septembers that stand out as miserably hot: 

2016: No one needs to be reminded of how Fall 2016 turned out. It was the worst wildfire season in history in East Tennessee, with a number of major fires, including the deadly Chimney Tops fire in the Great Smoky Mountains that spread into Gatlinburg on a horrifying, windy night in November. The hot and dry weather began that September, though it wasn’t too dry to start. September 2016 featured 2.25 inches of rain in Oneida — well below normal, but nowhere near the least amount of rain ever received in September. But the daily high temperature was, on average, 84.9 degrees, making it the third-hottest on record at the time, between 1998 and 2005 (85.0 degrees). September 2019 (currently at 88.5 degrees) may bump it down to fourth. There were eight days of temperatures at or above 90 degrees. The average nighttime low in September 2016 was above normal, but not terribly so, at 56.5 degrees. The heat and drought persisted after September. October featured less than an inch of rain and an average daily high of 76 degrees. It was an eye-popping 80 degrees on Halloween! November was also quite warm and quite dry, although things had begun to moderate by the end of the month.

2005: September 2005 was doesn’t make the list of Oneida’s Top 5 most miserable Septembers, but it was a hot one. In fact, its average afternoon high of 85.0 degrees makes it the second hottest ever, in terms of daytime heat. There were five days of temps in the 90s. But nighttime temps were quite comfortable, averaging 53.9 degrees. The month was quite dry, featuring only 1.16 inches of rainfall. The heat persisted into October that year, with temps in the mid 80s for the first week of the month, and hitting 80 degrees as lat was October 20. Once things broke, however, they broke in a hurry, and there were several consecutive nights of hard freezes (under 28 degrees) to end the month. November 2005 was a volatile month, with temps that were both well above and well below average. There were several mornings with temps bottoming out in the teens, which is unusual for November.

2002: September 2002 was one of the five miserable Septembers in Oneida. The issue wasn’t drought; the month wasn’t extremely wet, but it did feature 5.73 inches of rainfall. The average afternoon high temperature was 83.6 degrees — well above normal, but only tied for the third-hottest in Oneida’s history at that time (it’s since slipped into a tie for fifth, and will likely drop to a tie for sixth once September 2019 is in the books). Nighttime temperatures were above-average, as well, at 56.9 degrees. What made September 2002 seem a little less extreme by its end was the fact that the heat wave broke and the month ended comfortably. But, early on, it was miserable, with temps at 90 or above eight times in the first 11 days of the month and topping out at 93 degrees on September 10. Once the heat broke, it didn’t come back. October was quite benign, and November 2002 was actually quite a bit colder than normal. 

1999: Although it didn’t quite meet the standard of the September before it, September 1999 featured some very hot weather, with temperatures getting into the 90s six different days and very little rainfall (just over half an inch). The heat didn’t exactly go away; temps were well into the 80s at the end of the month, but low nighttime temps helped balance things out. In fact, the average nighttime low in September 1999 was 49.8 degrees, quite a bit below normal. Although October was benign that year, the above-average heat was back with a vengeance by November, with temps routinely getting into the 70s all the way through Thanksgiving.

1998: This one has already been described above, but 1998 — along with 1980 and 2016 — pretty much set the standard that September 2019 is proving to live up to. Daytime temperatures topped out at 86.7 degrees on average, making it the hottest September ever in that regard, and there were a record-setting nine days with temps in the 90s. Nighttime temperatures were above average, but not notably so. There was very little rain; less than half an inch in Oneida. The heat did not abate at any time during September 1998. It was a stunning 90 degrees on September 28! Things didn’t get much better in October, with a high of 86 degrees on the first day of the month and a high of 76 on Halloween. Highs were in the upper 70s the first three days of November, though temperatures began to moderate a bit as the month progressed. Warmth continued through December, as well.

1980: While hot Septembers (and, along with them, overall warm autumns and mild winters) have become quite normal since 1998, that miserably hot year marked the first time in a long time that it had been so warm so late in the year. The 1980s and 1990s featured crisp autumn and cold, snowy winters overall. But 1980 was an exception, going down as one of the hottest years on record in East Tennessee, with a persistent heat wave. September 1980 featured eight days with temps in the 90s, almost unheard of in Oneida at the time, including a high of 96 degrees on September 1. The average daytime high for the month was 83.1 degrees — the third-hottest year on record at the time, though it has since been bumped quite a ways down the list. The overall average temperature was 70.1 degrees — again, the third-warmest at the time, though it has since been bumped out of the Top 5. The heat wave didn’t end with September’s exit, either. It was a miserable 84 degrees on October 11 that year, and temperatures in the 70s persisted all the way into the last week of the month before cooler weather finally arrived. November finally brought seasonal temps, and even a couple of skiffs of snow. The heat returned temporarily in December, but temps bottomed out in the single digits on Christmas. 

1973: Prior to 1980, 1973 set the standard for September heat. There were five days of temperatures in the 90s, a record for the month at the time, and the average high temperature was 83.9 degrees, also a record at the time. The month was front-loaded as far as heat was concerned; the days in the 90s were the first five days of the month. But after a cool middle of the month, the heat returned later on, and temps were well into the 80s the last 10 days of September 1973. After that, the heat persisted into October. On October 4, the high temperature was a scorching 90 degrees — the only time 90 degrees has ever been recorded in Oneida during the month of October. And it almost happened again later on; the high reached 89 degrees on October 12. It was as hot as 80 degrees as late as October 28, and warm weather continued through the month of November. 

Eye to the Sky is a weather blog by Independent Herald editor Ben Garrett. Information on this blog should not be considered a substitute for forecasts, advisories or other products from the National Weather Service.