After an upper trough moved east, wind shear decreased, causing lower atmospheric pressures observations in Cozumel, Quintana Roo, Mexico.

Due to unfavorable conditions, Agnes leveled-off slightly in intensity and weakened to a minimal hurricane while approaching the Gulf Coast of the United States.

[2] Shortly before 2200 UTC on June 19, Agnes made landfall near Cape San Blas, Florida with winds of 75 mph (120 km/h).

[9] By early on June 21, a large extratropical trough spawned a low pressure area, which resulted in baroclinic activity.

In contrast, few observations of high tides along the east coast of Florida exist; the highest reported was 3 feet (0.91 m) above average in Jacksonville.

Initially referred to as a "windstorm", one of those twisters destroyed 50 mobile homes and a fishing camp in Okeechobee, as well as caused six fatalities.

[24] Effects were very minimal in Tennessee and limited to light rainfall in the eastern portions of the state, generally reaching no more than 3 inches (76 mm).

[31] The Peak Creek in western Virginia overflowed its banks, flooding a low-income housing area of Pulaski with water up to rooftops.

The Interstate 95 (I-95) Purple Heart Bridge over northern Virginia's Occoquan River was severely damaged and closed when rammed by a large barge carried by floodwaters.

The hardest hit area was the Patapsco River valley, with widespread destruction of buildings, roads, and railroads in the state park, at Daniels including its mill,[37] at Ellicott City, and Oella.

[34] The Patapsco flooded residential homes in parts of the county's North Linthicum, Pumphrey, and Belle Grove Road, Brooklyn Park neighborhoods.

[39] As a result of Agnes' rains, Conowingo Dam, astride the Susquehanna River just north of the Chesapeake Bay, recorded its all-time highest flow rate and stream heights.

The towns along the Susquehanna below the canal, Port Deposit, Perryville, and Havre de Grace, were flooded as torrents of water rushed through streets.

Late on June 23, a mandatory evacuation of Port Deposit's nearly 1,000 residents was ordered as the river continued to rise, causing the fire department to bring evacuees out by boat during an eight-hour period as over four-feet of water filled Main Street.

The Allegheny River reached above flood stage at several low-lying locations and at some places rose about 7 in (180 mm) per hour during the height of the storm.

More than one hundred Harrisburg YMCA campers and staff were evacuated using two CH-47 Chinook helicopters flown by the National Guard at Camp Shikellimy located downstream of DeHart Dam in Middle Paxton Township.

[43] A bridge collapsed in Danville, which caused two Penn Central diesel locomotives and several freight cars to fall into a swollen creek.

[44] In Chadds Ford Township in Delaware County, the Brandywine Creek crested at 16.5 feet (5.0 m), sending flood waters into the city.

The victims were Del Vaughn of CBS News and Sid Brenner and Louis Clark of WCAU in Philadelphia, and the pilot, Mike Sedio.

It is mainly regarded as the death of the Erie Lackawanna Railroad since the costs of damages were high and put the final dagger into the company.

Flooding in the upper Allegheny River basin was particularly exacerbated by the construction of the Kinzua Dam less than a decade prior; several towns in Cattaraugus County suffered extensive road and bridge damage that, four decades later, had yet to be repaired, with the state and local governments opting to abandon creek and river crossings instead of reconstruct them.

In Elmira, porches and garages were ripped loose, the Walnut St. bridge was carried away, Maple Ave. to Notre Dame High School was "underwater", and on S. Main St., Gerould's Pharmacy at W. Hudson was engulfed by 10 feet 3 inches (3.12 m) of water.

[24] Although no reports of abnormally high winds or rainfall exists in Ohio,[2] the storm caused minor damage to about 302 dwellings and severely affected at least three houses.

Strong winds felled trees and numerous limbs in Massachusetts, causing power outages and property damage in the western and central portions of the state.

High winds in southern and eastern Vermont knocked over trees and snapped off limbs, which resulted in scattered power outages, roads being blocked, and minor property damage.

[49] In western Cuba, Agnes dropped heavy rainfall, peaking at 16.76 inches (426 mm) on Isla de la Juventud.

Officials in that city believed that the National Weather Service and other media outlets made "exaggerated and erroneous" forecasts and reports on the storm.

Agnes had a devastating impact on the already-bankrupt railroads in the northeastern United States, as lines were washed out and shipments were delayed: The resulting cost of repairing the damage was one of the factors leading to the creation of the federally financed Conrail.

The levee also protected the area from the remnants of Tropical Storm Lee and Hurricane Irene in 2011, with the water cresting just barely below the height of the structure.

Conversely, the existing Kinzua Dam, built against the wishes of the Seneca Nation of New York, spared much of Western Pennsylvania from the worst flooding, by filling the Allegheny Reservoir to capacity.