On June 19, 1972, a minimal Category-One hurricane named Agnes came ashore near Panama City, Florida. While wind and storm-surge damage along the coast was small, the major impact from Agnes came afterward.
Agnes developed from a disturbance over the Yucatan peninsula on June 14th. As the system drifted eastward over the Yucatan Channel, it became more organized and was named a tropical storm on the morning of June 16th. It began to move slowly northward into the Gulf of Mexico. The research plane 40 Charlie had been deployed to Colorado to investigate mountain weather, but was recalled to Miami on the 17th by this early season threat. On the afternoon of June 18th, the plane flew a research pattern into the northward-moving storm and found it was deepening.
Agnes reached its peak wind speed of 86 mph (38 m/s) six hours later on the 19th. But as it approached the Florida panhandle, it began to weaken and was a minimal hurricane (75 mph [34 m/s]) when it made landfall near Cape San Blas, FL. The storm quickly weakened, but it brought along a large envelope of moist, tropical air and began to dump heavy rains on Florida, Georgia, and Alabama. Some thirty tornadoes were spun up in the periphery of Agnes throughout the southeast.
As it moved northeastward, an upper-level trough spawned a surface low to Agnes’ northwest which spurred it to re-intensify into a tropical storm. The two systems moved in parallel along the Eastern Seaboard causing extensive flooding along the Appalachian Mountains with rains of up to 19″ (48.3 cm). Agnes eventually transitioned to an extra-tropical system itself and continued to spread destruction into Canada, even generating another tornado in Ontario.
Agnes was responsible for 128 deaths, mostly in Pennsylvania where the state capital was flooded. Damage was estimated to exceed US$2 billion throughout the United States, making it the most damaging hurricane in American history to that point.