September 2018: Unseasonable Warmth and Drenching Rains!

Posted: October 2, 2018, 12:12 am by chewitt

So much for meteorological fall! It seemed summer was quite hesitant to depart the Northeast, making September yet another record breaker in various departments. While severe weather took a back seat, unseasonable warmth, high humidity, and drenching rainfall would define what is climatologically a rather quiet month.

A ridge allowed for high pressure to anchor itself over the eastern US in the first week, sending temperatures well above normal. High temperatures rose into the 80s and 90s, breaking several records between the 3rd and 6th. Washington, D.C. hit 95 degrees on the 4th while Philadelphia, Hartford, and Boston all broke records in the upper 90s! Humidity levels did not help matters either as dew points consistently hovered in the low 70s.

This quiet stretch would hit a wall come the 6th and 7th once a cold front sagged into the region, the former of which saw some damaging wind gusts in New England. Showers and storms along this also produced very heavy downpours due to the moist environment; over 4 inches fell near and over Philadelphia International while Reagan International received nearly 3 inches. This boundary would hang around over the next few days, mainly across southern PA, NJ, and most of the Mid-Atlantic, which added a few more inches to an already wet record in some spots. At the same time, the rainfall in combination with a cold front would send temperatures below normal by the 12th as highs struggled into the 60s.

 

An approaching thunderstorm in Westminster, MD on September 26th.
 

Hurricane season was now in full swing at this point and all eyes were glued to Hurricane Florence impacting the Carolina’s. A boundary separated the storm and high pressure over New England, keeping things dry for the most part outside of far southern Virginia. The remnants then swung into the Upper South along Appalachia, eventually moving through on the 17th and 18th, which brought a general 1-2” across the Northeast. This period up until about the 22nd was also marked by anomalously warm temperatures in the 80s, which sent departures 5 to 10 degrees above the norm.

A dry cold front then moved across on the 22nd, giving brief relief from the heat for the weekend. After the 24th though, a southerly flow surged summer-like air back into the area, sending temperatures once again well above normal. This was also marked by another stretch of active weather to round out the month. What was supposed to be a long duration rainfall on the 25th turned into a massive flooding event in northeast New Jersey before eventually spanning into the lower Hudson Valley and southwestern Connecticut. This was due to convergence along a warm front resulting in up to 3-5” inches across these parts, with locally higher amounts up to 6-8” between Norwalk and Meriden, CT! Many water rescues took place due to this excessive rainfall.

 

Destroyed roads and flooded streets across southern Connecticut on September 25th.
 

One final cold front then caused severe storms in Maryland, resulting in wind damage across the state. To add on to an already healthy amount of precipitation, an overnight disturbance a day later resulted in another 0.5-2” across Pennsylvania through southern New England.

Overall, this made for one of the more interesting Septembers we have seen in a while. The region was generally between 3 to 5 degrees above normal. In fact, Boston, MA recorded their 2nd warmest September on record. We also were in no way lacking in precipitation as much of the Northeast was 3 to even 6 inches above normal, resulting in amounts in cities that were up to triple their normal! Now that October is upon us, hopefully fall finally makes a more extended appearance this month.

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