Severe Weather, Tornadoes, and Flooding in August

September 12, 2023 // Article by: Steven Weinstein

Although bouts of severe weather and tornadoes were prominent during the first half of August 2023, it was not nearly as active from a severe weather and flash flooding perspective as June and July were. While there were still some systems spread out throughout the month, more prolonged drier stretches were notable, allowing many to soak up the last few days of summer. Meanwhile, any heavy rainfall events were localized, leading to quite the spread in precipitation anomalies across the Northeast, and temperatures were slightly below to near normal.

The first week of August marked a nice change from the oppressive heat and humidity seen in July with a drier, cooler, and September-like airmass settling in. As such, many areas ran 5 to 10 degrees below normal with cities such as Hartford, Philadelphia, and Atlantic City also setting daily record lows in the mid-50s to the low 60s. However, this cooler spell did not last long with the end of the week bringing the return of more summerlike heat and humidity across the Northeast. This helped fuel an afternoon/evening round of storms on the 6th that led to some localized heavy rainfall across parts of New Jersey, Pennsylvania, and down into the Mid-Atlantic. Then, as a warm front lifted north during the morning hours of the 7th, this primed the atmosphere for a rather significant bout of severe weather later that day across the Mid-Atlantic. For many across Maryland and Northern Virginia it was the area's first moderate risk for severe weather (risk level 4 out of 5) issued by the Storm Prediction Center (SPC) in over 10 years! A destructive line of storms traversed the Mid-Atlantic before entering into Eastern Pennsylvania and Southern New Jersey. This led to widespread damaging wind reports as many trees were uprooted, power poles were snapped, and some structural damage resulted. Additionally, 5 brief EF-0 and EF-1 rated tornadoes were confirmed, 2 in York County, PA, 1 in Lancaster County, PA, 1 in Lehigh County, PA, and the last one in Hunterdon County, NJ. 

Activity associated with this system then shifted eastward into New England the following morning with repeated downpours and storms leading to swaths of heavy rainfall across Connecticut and Massachusetts. This was especially the case in the Merrimack Valley in Massachusetts and Southern New Hampshire where 3-5"+ of rainfall fell, leading to numerous flash flooding issues. 2 brief tornadoes were also confirmed across Southeastern Massachusetts during the morning hours, an EF-1 in Plymouth County and an EF-0 in Barnstable County. An active second week of the month continued, first in the form of a system on the 10th that led to a few wind damage reports in Southern New Jersey as well as 2 EF-1 rated tornadoes across Gloucester and Burlington Counties in NJ. This activity was then followed up by another round of strong PM and overnight storms on the 12th that produced swaths of wind damage across portions of New Jersey, Pennsylvania, the Hudson Valley, and Connecticut. Isolated large hail occurred with some of these storms with an EF-0 tornado also touching down in Litchfield County, CT. Furthermore, it was during the second and third weeks of August that sporadic daily record highs in the upper 80s to even the upper 90s were set across many Northeast climate stations. After this, the third week of the month was relatively quiet with plenty of dry time as high pressure reigned supreme for many. 

Retweeted photo by NWS Mt Holly of quarter sized hail from strong storms in Bucks County, PA on August 12th, 2023.

An exception to this was a system into the morning of the 18th which brought heavy rainfall to much of New England with 1.5-3"+ falling. However, it was again the severe weather aspects of this activity that made it most memorable with a localized tornado outbreak occurring across Eastern Connecticut, Rhode Island, and Southeastern Massachusetts. At the culmination of the event, 5 tornadoes touched down across these areas over the span of just a few hours, with 1 occurring in CT, another in RI, and the last 3 in MA. Meanwhile, the Rhode Island tornado that tracked through Scituate, Johnston, and North Providence was given a more significant EF-2 rating, with estimated winds of up to 115 mph! Unfortunately, 1 person was injured by this tornado and the event served as further proof to just how active this year has been tornado wise. During the third and fourth weeks of the month, temperature swings were common across many Northeast cities, with above normal days followed by days that saw temperatures run as much as 3 to 8 degrees below average. Indeed, just as there were record highs there were also daily record lows in the upper 50s to the low 60s set during this timeframe.

Tweet from NWS Boston revealing the paths of the tornadoes that impacted New England on August 18th, 2023.

Outside of a batch of showers and storms for much of the Northeast on the 25th and a round of heavy rainfall on the 28th for portions of Southeastern Virginia which brought locally 2-4", the weather was relatively mundane to close out meteorological summer. Perhaps the most notable weather story during this timeframe was the uptick in tropical activity. Thankfully, these storms such as tropical cyclone Idalia stayed away from the East Coast. Nevertheless, Hurricane Franklin, which tracked well out over the open waters of the Atlantic, was still able to produce dangerous rip currents all up and along the Eastern Seaboard during the last several days of the month.

NWS Baltimore-Washington tweet showing high clouds which were in association with Idalia passing through the Carolinas.

Overall, high and low temperatures largely ran around normal to even a degree below normal across the Northeast during the month of August. Precipitation wise, anomalies were far more variable from site to site than previous months, especially across New Jersey, Pennsylvania, and the Mid Atlantic. Specifically, while the northern parts of NJ and PA ran 1-1.5" above normal, it was the southern portions of these states that ran 0.5-2" below their normal monthly rainfall. Meanwhile, anomalies were even more sporadic into Maryland and Virginia with amounts generally running 1" above to 1" below normal. It was New England that was more consistent with most areas finishing 0.5-1.5" above their normal monthly rainfall (though the Merrimack Valley was an exception). Lastly, pesky drought conditions currently continue across Northwest Maryland to end the month.