The Hurricane Ivan tornado outbreak was a three-day tornado outbreak that was associated with the passage of Hurricane Ivan across the Southern United States starting on September 15, 2004, across the Gulf Coast states of Alabama and Florida as well as southern Georgia before ending in the Middle Atlantic Coast on September 18.

[5] On September 13, 2004, as Category 5 hurricane Ivan moved through the Yucatán Channel,[6] the Storm Prediction Center noted the possibility of isolated tornadoes for parts of Louisiana and the Florida Panhandle three days out.

[7] Though the storm weakened while approaching the United States, strong low-level wind shear along its northeastern periphery allowed for the development of potentially tornadic supercells.

[8] A National Oceanic and Atmospheric Administration Hurricane Hunter aircraft intercepted Ivan during the afternoon and evening of September 15.

A thermodynamic sounding around 1:00 p.m. EST from Tampa Bay, Florida revealed unusually favorable conditions for deep, rotating convection.

[9] The significant levels of CAPE, accompanied by a dry air intrusion between the rainband and the main convection of Ivan, were the primary cause of the outbreak.

Over the course of the next 20 hours, the National Weather Service (NWS) office in Tallahassee monitored over 50 mesocyclones that had sufficient vorticity to spawn tornadoes.

[1] By the afternoon, downstream subsidence limited thunderstorm activity; however, as the day wore on, sufficient warm, moist air from the Gulf Stream and breaks in cloud cover allowed for CAPE values to rise.

[15] Following a lull in activity during the overnight hours between September 16 and 17, conditions once more became increasingly favorable for tornadoes across North Carolina and Virginia.

[20] As the remnants of Ivan, now a tropical depression moved further inland, increased instability and thunderstorm cells produced a large tornado outbreak from the northern Carolinas to Pennsylvania.