Monday, June 18, 2012

Forty Years of Agnes: Landfall

Forty years ago tomorrow, Hurricane Agnes made landfall along the Florida Panhandle as a minimal hurricane.  Agnes was pulled northward by a developing trough in the Eastern US, as well as a stalled cool front that was lying across the Delaware Valley.  This front was the first piece of what amounted to an awfully rainy period that began mid month with the front's approach.

While Agnes approached with 75 mph winds, our region dealt with a rather rainy 18th as the front stalled and a wave of energy travelled along the front.   Rainfall on the 18th, not associated with Agnes, totalled 0.94" in Harrisburg, 1.41" in Allentown, and a half inch or above in Atlantic City, Philadelphia, and Scranton.  For Allentown, the rainfall total was compounded on top of an inch of rain that fell on the 16th.  While these rains weren't heavy by themselves, the ground was increasingly soggy.

You can see the graphic below from the 19th showing Agnes approaching Florida and the cold front stalled out near us.

In Florida, Agnes' impacts were in the variety of severe weather.  Over twenty tornadoes touched down in Florida, injuring over 140 and killing seven.  400 mobile homes were either damaged or destroyed.   One of the unique characteristics of Agnes was that the storm featured some non-tropical characteristics with frontal banding that you can see on satellite imagery at the top of the post.  The frontal banding was conducive to tornadic development and helped spawn the outbreak.

After landfall on Monday night, the storm moved little until the 21st as a second cool front approached from the west.  This second front...and the slow moving Agnes, combined to cause the epic floods that followed later in the week.