Hurricane Ivan tornado outbreak
| Type | Tornado outbreak |
|---|---|
| Duration | September 15 – 18, 2004 |
| Tornadoes confirmed | 120 (Record for a continuous outbreak in September) |
| Max rating1 | F3 tornado |
| Duration of tornado outbreak2 | 2 days, 14 hours, 17 minutes |
| Damage | $96.9 million |
| Current advisories | Southern and Eastern United States |
|
1Most severe tornado damage; see Fujita scale 2Time from first tornado to last tornado Part of Hurricane Ivan and the tornado outbreaks of 2004 |
|
1Most severe tornado damage; see Fujita scale 2Time from first tornado to last tornado
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.
The outbreak killed 7 people and injured dozens of others across several states from Florida to Pennsylvania. The hurricane itself killed at least 90 people from the US to the eastern Caribbean Islands. Overall it produced 120 tornadoes surpassing the record of 117 that was previously held by Hurricane Beulah during the 1967 Atlantic hurricane season. Ivan also produced 16 more tornadoes than Hurricane Frances which struck most of the same regions (the tornado outbreak) about ten days earlier.
On September 13, 2004, as Category 5 hurricane Ivan moved through the Yucatán Channel, the Storm Prediction Center noted the possibility of isolated tornadoes for parts of Louisiana and the Florida Panhandle three days out. 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. A National Oceanic and Atmospheric Administration Hurricane Hunter aircraft intercepted Ivan during the afternoon and evening of September 15. During the mission, dropwindsondes were deployed off the Gulf Coast to assess the rainband environment. By this time, an intense band of thunderstorms, with embedded supercells, developed about 250 mi (400 km) east of the hurricane's center. A thermodynamic sounding around 1:00 p.m. EST from Tampa Bay, Florida revealed unusually favorable conditions for deep, rotating convection. Ahead of the band, convective available potential energy (CAPE) levels reached 2,500 J/kg and significant helicity. 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. A comparison between Ivan and Hurricane Jeanne revealed that both storms encountered similar conditions near landfall; however, CAPE values were lower during Jeanne and the system produced far fewer tornadoes.
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