Hurricane Ivan, Virginia’s largest tornado outbreak – September 17, 2004

Hurricane Ivan track with designated intensity. Track data from NOAA Coastal Services Center (http://csc.noaa.gov//hurricanes). Map by Kathryn Prociv

Hurricane Ivan track with designated intensity. Track data from NOAA Coastal Services Center. Map by Kathryn Prociv.

The largest tornado outbreak in Virginia history occurred on September 17, 2004, when the remnants of Hurricane Ivan impacted the Mid-Atlantic.

38 of 58 tornadoes that day touched down across Virginia. On the other side of the Potomac, six touched down or passed into Maryland. Several others impacted Pennsylvania and West Virginia.

The larger Mid-Atlantic outbreak from Ivan had the most tornadoes of any event in the region since modern tornado records began in 1950, and the one-day total in Virginia is the largest daily tally of any state east of the Appalachians and north of South Carolina.

Ivan also had more tornadoes recorded overall than any other hurricane in modern history, with 118 reported along its track.

Hurricane Ivan and its tornado production

Ivan made landfall near Gulf Shores, Alabama on September 16, 2004 as a category 3 hurricane.  After making landfall, it weakened to a tropical depression and took on extratropical characteristics as it moved north and east along the spine of the Appalachian Mountains.

Tornadoes are very common with tropical systems; at least one-fourth of land-falling hurricanes produce tornadoes. The main mechanism for tornado development from tropical systems is a highly sheared environment. In other words, an environment that has varying winds of different speed and directions at different heights through the atmosphere.

18z (2 p.m) surface pressure shows the center of Ivan's remnants over western North Carolina and southwest Virginia. A mid-level low was focused a bit to the north over West Virginia. (Storm Prediction Center)

18z (2 p.m) surface pressure shows the center of Ivan’s remnants over western North Carolina and southwest Virginia. A mid-level low was focused a bit to the north over West Virginia. (Storm Prediction Center)

Tornadoes in a tropical cyclone are most prolific in the right front quadrant of its forward direction, where shear is maximized due to several factors.

In the case of Hurricane Ivan locally…

1) Surface winds were strongly “backed” to the southeast along and to the east of the main bands of precipitation.  At the same time, some mid-level dry air ingested off the continental landmass helped foster areas of sunshine that allowed for just enough instability (on the order of 500-1,5000 CAPE) to produce discrete supercellls within the bands of precipitation. Additionally, surface winds were influenced by the frictional and topographic influences of the regional landscape.

2) Hurricanes often produce most of their tornadoes near the coast. Ivan did do a lot of that prior to reaching the region on its day of landfall, and tornadoes were again maximized in a region closer to the coast on the day they occurred around here.  The mid-level storm was also exhibiting extratropical characteristics by the time it impacted us, with the mid-level low taking on a “negative tilt.” Both factors favored a higher end event.

3) Other standard tornado-producing ingredients include the winds with height associated with the clockwise flow of the cyclone. These winds were generally flowing in a southerly direction around the storm center to the southwest of our area. Upper-level steering winds from the west and southwest, first directing the storm northward inland and eventually northeastward toward the Mid-Atlantic also acted as the change in winds at different levels required for tornado formation. As noted above, strong surface backing to the southeast promoted low-level spin nicely.

18z (2 p.m.) temperatures and dew points. Dew points were well into the 70s across the region. Primed for tornado activity. (Storm Prediction Center)

18z (2 p.m.) temperatures and dew points. Dew points were well into the 70s across the region. Primed for tornado activity. (Storm Prediction Center)

Tropical systems are a regular contributor to the region’s tornado climatology, given that we tend to see the remnants of these storms pass by with relative frequency. Ivan stands out for the number of tornadoes it produced, not because of the area it affected.

Tornado reports

In total, Hurricane Ivan spawned 118 tornadoes across nine different states. This is the highest known total from a tropical system on record.

Tropical systems which impact the United States from the Gulf of Mexico are the predominant tornado producers, with storms like Hurricane Rita and Katrina in 2005 producing 101 and 58 respectively.

It is worth briefly noting there is little correlation between storm strength and tornado production, though hurricanes are the more prolific tornado-producers, generally.

Tornado tracks with Fujita Scale rating across the D.C. area.  Tornado data from the Storm Prediction Center. Map by Kathryn Prociv.

Tornado tracks with Fujita Scale rating across the D.C. area. Tornado data from the Storm Prediction Center. Map by Kathryn Prociv.

In the case of Hurricane Ivan, perhaps somewhat surprisingly, the state of Virginia topped the list for tornado numbers with its 38.  Georgia experienced the second most tornadoes from the event with 25.

Tornadoes by state = Virginia: 38 | Georgia: 25 | Florida: 18 | Pennsylvania: 9 | Alabama: 9 | South Carolina: 7 | Maryland: 8 | North Carolina: 4 | West Virginia: 3

Of all the tornadoes, only 15 percent were strong, classified as F2 or greater.  It is very common for most tornadoes associated with tropical systems to be short-lived and weak, consistent with a higher shear but lower instability environment.

All Ivan tornadoes by ranking = F0: 48 | F1: 52 | F2: 17 | F3*: 1

*The only F3, and strongest tornado of the event, occurred in Virginia, near Culpeper.

Impact on the D.C. area

The larger local region was especially hard hit, with the greatest density of tornado concentration occurring south and west of the District. The immediate D.C. area was largely spared, at least comparatively.

Hurricane Ivan (Storm Prediction Center)

September 17 afternoon radar loop. (Storm Prediction Center)

The majority of tornadoes  in the D.C. area tracked in almost a due south to due north trajectory, often with a bend slightly west of due north.

The longest tornado track across the D.C. region was an F2 that tracked 15 miles from just south of I-66 in Fairfax County all the way north of Poolesville, Maryland.  This was the same tornado that passed very close to Dulles International Airport.  Another notable tornado track was the only F3 tornado, that traversed 9 miles through Fauquier County near Culpeper.

Take a look at the density of tornado warnings across the D.C. area below. Two patterns to take note of include not just the north-south orientation of the warnings but also how narrow the corridor of warnings was.

The outer rain bands associated with the remnants of Hurricane Ivan trained over the same relatively small spatial area, causing several of the same locations to experience several tornado warnings and associated tornadoes.

All tornado warnings issued for Ivan (see local closeup with tornado touchdown locations).  Tornado warning data courtesy of the Iowa Mesonet and tornado data courtesy of the Storm Prediction Center.  Map by Kathryn Prociv.

All tornado warnings issued for Ivan (see local close up with tornado touchdown locations). Tornado warning data courtesy of the Iowa Mesonet and tornado data courtesy of the Storm Prediction Center. Map by Kathryn Prociv.

Thankfully, no one was killed by the tornado outbreak in the area.  Given the large number of tornadoes, even the 12 injured locally seems like a small number. This can be attributed partly due to the weak nature of many of the tornadoes, but also, perhaps more importantly, many of the tornadoes went through wooded or less populated areas.

Even with that eventuality, at least 25 homes and businesses were destroyed across the state of Virginia, with more than 2,000 heavily damaged. A large part of that tally came from Henry County near the southern border of the state. Sporadic reports of significant damage were also particularly notable in parts of Loudoun, Fauquier and Fairfax counties.

The swath of tornado tracks occurred within a narrow corridor on the western edge to the lower Maryland Peninsula on the eastern edge; an areal width of just 75 miles.  If the main tornado corridor was offset just 10 miles east many of the tornadoes would have traversed straight through the heart of downtown D.C.  If offset 30 miles to the east?  They could have swarmed Baltimore.

Infrared satellite around 4 p.m. on September 17, 2004 as Ivan's tornadic storms were impacting western parts of the D.C. area. (Storm Prediction Center)

Infrared satellite around 4 p.m. on September 17, 2004 as Ivan’s tornadic storms were impacting western parts of the D.C. area. (Storm Prediction Center)

In perspective with other tornado days locally

54 tornadoes touched down in the broader Mid-Atlantic** on September 17, 2004. That’s almost double the second highest day in the region. That spot is held by June 2, 1998 when 30 tornadoes (out of 37 total) struck, mostly in Pennsylvania but including the Frostburg F4. Five other dates have brought 20-25 tornadoes to the region: July 27, 1994 (25), May 31, 1985 (21), May 31, 1998 (21), April 27, 2011 (20), and June 1, 2012 (20).

When it comes to a state-by-state comparison, the tally is also quite impressive. The 38 tornadoes touching down in Virginia on September 17 bests every other state’s record in the larger northeast United States (including back to Ohio, Kentucky, Michigan), bounded by South Carolina to the south.

Interestingly enough, South Carolina’s 42 tornadoes in one day was set the same month, on the 7th during Hurricane Frances. That storm was also a prolific tornado producer, dropping 89 up the eastern seabord, including 14 in Va. and one in Md.

A tornado as seen in western Fairfax County, Va. (NWS Baltimore/Washington)

A tornado as seen in western Fairfax County, Va. (NWS Baltimore/Washington)

The 38 tornadoes in Virginia topped the previous daily high of 18 on August 6, 1993. That event focused on southeast Virginia and into North Carolina. It produced an F4 that killed four people not too far from Richmond.  14 tornadoes is the third daily high for Va., and amazingly that number also happened on August 30, 2004 (Gaston).  2004 was the year of the tornado in Va.!

In the immediate D.C. region, Maryland’s top tornado day occurred on July 27, 1994 (14), West Virginia’s was on June 2, 1998 (7), and Delaware July 15, 1992 (4, and others). Our neighbors further north in Pennsylvania and North Carolina have maximum tornado days of 21 and 31 respectively.

**Mid-Alantic as noted here includes tornadoes impacting or potentially impacting Pennsylvania, Virginia, Maryland, New Jersey, West Virginia, Delaware, D.C.

Additional Ivan tornado reading…

Storm Prediction Center local tornado watches: #1 | #2 | #3

SPC discussions: 12:33 p.m. | 1:37 p.m. | 3:33 p.m. | 3:53 p.m. | 6:19 p.m. | 9:58 p.m.

SPC outlooks: 2 a.m. | 9 a.m. | 12 p.m. | 4 p.m.

NWS Baltimore/Washington Ivan review | NWS Raleigh NC Ivan review | NWS State College Ivan review

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