New Orleans multi-vortex tornado rated ‘at least’ EF3, strongest since 2017

The Weather Service office in New Orleans was surveying the damage from the tornado Wednesday and wrote that the EF3 rating is preliminary.

“A final assessment including results of the entire survey [is] expected to be completed and transmitted via a public information statement in the next day or two,” a Weather Service statement said.

The EF3 damage was found near Arabi in St. Bernard Parish, La., which was hardest hit by the twister. Numerous houses were flattened, and some were moved off their foundations, as the large tornado tore through the area.

Tuesday night’s tornado is the strongest to strike New Orleans since an EF3 on Feb. 2, 2017, struck just a few miles to the north of Arabi. That tornado damaged hundreds of homes and injured dozens of people. Depending on its final rating, it’s not out of the question Tuesday night’s tornado could become the strongest on record in the city.

The tornado appeared to contain multiple vortexes, with at least one additional funnel orbiting around a primary wedge-shaped cone.

In the wake of the tornado, many took to social media or to websites to learn more about “multivortex.” It’s exactly what it sounds like — a tornado with smaller whirls, or vortexes, within it. There’s an age-old expression in meteorology: “Spin begets spin.” Large, rotating low-pressure systems tend to have smaller eddies of low pressure within them, and the same can be true with powerful tornadoes.

The multivortex nature of some tornadoes is the reason that some of the damage left behind is erratic, irregular and seemingly random. It’s because of the compounding effects of wind. If you have a 90 mph “subvortex” rotating around a 70 mph “main vortex,” a narrow swath will get a double-whammy, 160 mph wind. Conversely, someone in a sweet spot where the subvortex’s winds are opposing those of the main funnel might see winds of 20 or 30 mph. That’s why one house may be obliterated with a neighboring one undamaged.

Tuesday night’s tornado probably was a multivortex one at some points in its life cycle. The image that went viral, however, is of a serpentine-looking whirlwind extending from the main vortex. That’s what storm chasers refer to as a “noodle.” There’s so much “vorticity,” or spin, surrounding the strongest tornadoes that some of it can pinch off and form additional whirls. It’s also a testament to the extreme upward velocity of the primary vortex. Pay attention to the rising motion seen in videos as the funnel churns along the ground.

Atmospheric scientists think that most significant tornadoes are, at one time or another, multivortex. Contrary to popular belief, the strongest winds in tornadoes aren’t at their core, because of the multiple vortices, but are often at the edges.

Multivortex tornadoes are not to be confused with satellite tornadoes, which are secondary tornadoes, usually ropelike, that touch down a half-mile or more away from a larger tornado and orbit around it. They’re tougher to spot on radar because they exist in the larger tornado’s mesocyclone, or broader rotation.

Storm chasers have been caught off guard, even injured, by satellite vortexes. On May 28, 2019, a satellite vortex flanking an EF4 tornado west of Kansas City knocked two vans carrying passengers of Silver Lining Tours, a storm chase tour company, into a field.

Tornadoes have struck the area around New Orleans repeatedly in recent decades.

Within the metro area of New Orleans (17.5 miles or less from city center), there have been 75 tornadoes since 1950. A number of years have seen multiple twisters. In 2016, four were recorded.

Given their proximity to the warm Gulf of Mexico, the northern Gulf Coast and Louisiana can experience tornadoes throughout the year. They are most common in New Orleans in May, when 16 percent have formed. March has produced just 5 percent of the city’s tornadoes.

More than 80 percent of New Orleans-area tornadoes in the modern record have been weak, or rated 0 to 1 on the EF scale or its predecessor, the F scale (before Feb. 1, 2007). Just the 2017 twister received an EF3 rating, while 16 percent were rated EF2 or F2.

In December 1983, an F4 affected LaPlace, about 25 miles west-northwest of New Orleans. A dozen violent (rated 4 or 5) tornadoes have struck Louisiana in the modern record, with the strongest an F5 in February 1971.

For residents of New Orleans, Tuesday’s tornado was yet another punishing event among multiple highly destructive natural disasters that have walloped the city, and Louisiana, in recent years.

Just seven months ago, Category 4 Hurricane Ida slammed into Louisiana’s southeast coast. New Orleans experienced severe freshwater flooding from the storm’s heavy rain, and wind gusts to 113 mph knocked out almost 100 percent of the city’s power.

Ida’s rampage followed the 2020 hurricane season, in which four tropical cyclones made landfall in Louisiana. Category 4 Hurricane Laura devastated a wide swath of the state’s southwest, near Lake Charles, and Category 3 Hurricane Zeta battered New Orleans with damaging winds.

Catastrophic flooding also struck much of southern Louisiana in August 2016, as 20-30 inches of rain fell over a multiday period. According to the National Centers for Environmental Information, the 500-year rain event caused more than $10 billion of damage across the state in the nation’s costliest flood since Hurricane Sandy struck the East Coast in 2012.

Every 21st century disaster to strike New Orleans and Louisiana exists, to an extent, in the shadow of 2005’s catastrophic Hurricane Katrina. Among the worst natural disasters ever to strike the United States, the Category 3 storm shoved a record-breaking storm surge over the city’s levees in a flood that killed 1,833 people and caused nearly $200 billion of inflation-adjusted damage.

Katrina’s flood was particularly devastating to New Orleans’s Lower Ninth Ward, where a number of levee breaches resulted in many hundreds of deaths. Tuesday’s damaging tornado directly struck the same ward.