080616 Tornado path damage _lowres

The New Orleans tornado that destroyed three homes in Treme and the 7th Ward on Thursday was a strange, weak and short-lived phenomenon that popped up with essentially no warning, the National Weather Service said Friday.

The storm likely would have caused little lasting damage — though it did hurl a trampoline into some power lines — but for the fact that the three buildings in its path were blighted, though there was no prior indication they were likely to fall down in the immediate future, city officials said.

That a tornado broke out at all — even one that barely qualified for the name — caught forecasters by surprise.

When the storm popped up over the New Orleans area, it didn't have the traditional marker of a system that produce tornadoes, said Kenneth Graham, the meteorologist in charge at the National Weather Service office in Slidell.

Typically, tornadoes develop out of storm systems that are themselves rotating, and it's that motion that alerts forecasters to issue tornado watches and warnings, Graham said. That was not the case with Thursday's storm.

"We did put out a special statement and a severe weather warning," he said. "There's no tornado warning when they're that short-lived. It's tough to see them on the radar."

The tornado touched down over a half-mile path, roughly from Kerlerec Street to North Claiborne Avenue, and topped out with winds of about 80 mph. That put it in the lowest category of the scale used by meteorologists to rate tornadoes.

In fact, meteorologists were somewhat cautious about referring to it as a tornado at all.

While they were examining the debris Thursday evening, they saw some signs that the winds had been rotating, including some shingles on homes that had been shifted around.

Most of that damage was confined to about a block at the start of the storm's brief path of destruction, near the old McDonogh 35 High School building and the first house that fell, at 1326 Kerlerec. That home, a vacant two-story building, damaged a nearby house when it collapsed.

From there, the storm moved toward Claiborne, where it caused the collapse of a vacant two-story home at St. Philip Street and destroyed half of anther two-story building at Ursulines Avenue.

Exactly what happened with the storm is not entirely clear, but Graham suggested the tornado may have been followed by a down burst — cold air that had been forced higher into the atmosphere and then rushed downward — that extinguished the tornado itself.

Each of the three destroyed buildings was being reviewed by the city's Code Enforcement Department before the storm. None had been judged to be in imminent danger of collapse — the standard used for determining whether the city should step in and knock down a building — though those inspections dated to between 2010 and 2014, said Jared Munster, the city's director of safety and permits.

"I don't believe that, but for these winds, these buildings would have come down on their own," Munster said.

The owners of all three buildings also had at least begun the process of getting approval to demolish the buildings, though those efforts appear to have stalled. The most recent one to get approval was the St. Philip building, which was cleared for demolition on June 2; the other two were cleared for demolition years ago, but no work was done.

The collapses spilled debris out into the roadways, closing them until crews could get them clear about 10:30 p.m.

The property owners will be responsible for footing the bill for the cleanup. If they don't pay, liens will be put on their properties to collect the money, city spokeswoman Sarah McLaughlin said.

Overall, tornadoes are rare on the east bank of Orleans Parish, largely because of a sheet of moisture from the Gulf of Mexico known as the "marine layer," Graham said. That dense, stable layer of air has the effect of stifling the volatility of storms and preventing tornadoes from forming, he said.

Still, especially after a day of extreme heat, tornadoes can occur in the city itself.

"They're not real common, but they do happen," Graham said.