Next week will mark the forty year mark of Agnes' impacts in this region -- setting flood marks that were not approached or breached until last year. If it weren't for Agnes, last year's flooding in Central Pennsylvania would have been the "Agnes" that likely changed the face of many a town.
Forty years ago this weekend, Agnes was developing as a tropical system and lifting northward into the Yucatan Channel that separates Cuba from Mexico. The storm was just a tropical storm at the time but would intensify into a hurricane over the "Loop Current" in the Gulf on the 18th. Early projections of the storm making landfall over Western Cuba and tracking through Florida misfired as the storm took a more western track, allowing it to stay over open water as it progressed northward.
Locally, our region was somewhat dry and had dealt with a coolish pattern for the most part in June. Rainfall in early June was running about an inch below average in Philadelphia, an inch and a half below average in Allentown through the 15th. Less than a week prior to Agnes' intro to our region, temperatures had dropped into the 30's in Allentown on the morning of the 11th as frost occurred in the Poconos. However, by the 16th a frontal boundary approached the East Coast and brought a decent round of rain and thunder to the region -- Allentown picked up 1.15" of rain on the 16th, Scranton picked up 0.70" of rain between the 15th and 16th. The front slowed as it crossed the region and the associated upper trough behind it set up the path of least resistance that allowed Agnes to come farther north. We'll talk more about that down the line but this front as it approached set the table for Agnes to come north.
The tropics in 1972 weren't even that active -- four tropical systems, three subtropical systems in a developing El Nino year and a cool phase in the Atlantic. The combination made for a not-so-active season but Agnes was the most notorious...and a nail in the coffin to support the theory that it only takes one storm to make a year noteworthy.