September weather outlook for D.C.: Hot and dry

Following a June through August in which heat was seldom excessive, the air is delightfully cool and fresh as we start September. But summer is not finished with us yet.

A summer sizzle is set to strike the D.C. area starting Monday, with highs in the mid-to-upper 90s for a three-day stretch. Highs may surpass 90 for six straight days starting Sunday, and that, by itself, may be enough to ensure a hotter-than-average September.

We project the District’s September average temperature to be 1 to 3 degrees above the norm (which is 72.4 degrees) following our first cooler-than-average meteorological summer (June through August) since 2017.

The upcoming hot weather predicted for the area is part of a spell of nationwide heat. Averaged across the Lower 48, the first half of September is forecast to be the hottest on record for all years back to 1950:

The hot pattern won’t lend itself to much rain. Computer models project drier-than-normal weather for the first half of September over much of the Mid-Atlantic:

Given these models, we project September will see 0.5 to 2 inches less rain than normal, which is 3.93 inches.

Advertisement

While there is high confidence it will be hot and dry through the first third of the month, the latest model projections show cooler changes by the week of Sept. 11 that should offer some autumn flavoring again. Highs should shift back into the 70s, and rain chances should increase too.

August and summer recap

Looking back at August, the month ended up slightly cooler than normal at 78.7 degrees (or 0.7 degrees below the 1991-2020 average). It marked the first cooler-than-normal August since 2017. However, considering normals are based on the period from 1991 to 2020, and temperatures have warmed over the long term, it still ranked as the 38th hottest August since 1871.

In our outlook released a month ago, we projected an average August temperature of 79 to 80 degrees, so we missed that range by a mere 0.3 degrees.

Advertisement

Across June, July and August, the summer average temperature was 78.1 degrees, which was 0.8 degrees cooler than normal, also the lowest since 2017. But it was still the 35th hottest on record since 1871.

August rainfall totaled 3.71 inches, which was 0.46 inches wetter than normal in the District; however, both Baltimore and Dulles had drier-than-normal months. In our outlook released a month ago, we projected 3 to 5 inches for the District.

The 3.71 inches marked the District’s 71st wettest August on record, while the June-to-August total of 12.27 inches was 0.49 inches wetter than normal and the 68th wettest.

Overall, Washington had a mix of warm and cool days during August, with cooler-than-normal days somewhat more numerous — as shown in the calendar below:

There was little in the way of extreme weather during the month. Dulles was the only observing station to set a record, when it tied the Aug. 25 calendar day high mark of 97.

For the year overall, 2023 is now tied with 2017 for the second hottest on record in the District, and precipitation is running slightly below normal.

ncG1vNJzZmivp6x7uK3SoaCnn6Sku7G70q1lnKedZMSmrdOhnKtnYmV%2FdHuPcmZpaV%2BZsG6%2FxKmrnqWSmr9uw8Saq6GdomK8tsDLqKakZZikwXA%3D