We just had the warmest September since the 1920s here are the charts to prove it.

This likely is not a huge shock to many around here, but this September was insanely hot. September is usually a month that starts warm with average highs in the mid-80s and lows in the mid-60s. Then by the end, we usually see highs in the upper 70s and lows in the mid-50s. This year was anything but normal.

The temperature records for Charlotte are from 1878-2018, but dew point records only date back to 1941.

Average overall temperature:

This number should be around 70° which is all the highs and lows averaged out over the entire month. This year we had the 3rd warmest September on record and warmest since 1925.

Average High Temperature:

The daytime high we had were much higher than average, but we only hit 90° or higher 11 times. Which was high but fell to the 14th most on record. This made September the 7th warmest September for an average high temperature of 87.3°.

Average low temperature:

If you want to know why this September was so warm look no further than the overnight low temperatures. The low temperatures were anything but low. This was crazy warm for a month that even with warm days we should start to see cooler nights, not the case this year this was by far the warmest September on record for overnight low temperatures.  The average low for the month is 10.4° cooler than this year.

How bad was it? For the 1st time since 1933, we didn’t see a low temperature in Setepmber below 60°. That means no lows in the 50s as all this September.

It was crazy muggy as well:

One thing that drove these warm overnight low was the incredibly high dewpoints. The very muggy airmass typical of summer hung out over the Southeast and kept our overnight lows from dropping at all. Remember dry air cools much easier than moist air. This was far and away the muggiest September since we started keeping dewpoint records in 1941. This chart shows the number of hours with dewpoint at 70° or higher.

Rainfall:

That muggy air and Hurricane Florence also made for a very wet September. It was the 5th wettest Setepmber on record.

The cause?:

The cause was the persistence of the Subtropical ridge we call the Bermuda high. This semi-permanent high drives our summer weather but usually starts to break down and shifts South and east back into the Atlantic as Sepapproachesrocahes. The jetstream also starts it annual shift back south, and cold fronts are driven into the region. This year both the ridge moves closer t us, got stronger and the jet stream stayed north. This not only made us hot but also very muggy and we weren’t alone a big chunk of the eastern U.S. saw the same pattern.