NASA's Aqua satellite passed over Tropical Storm Isaac on Aug. 26 at 18:15 UTC (2:15 p.m. EDT) when it was over Florida and Cuba and the MODIS instrument captured this visible image of the storm.
Credit: NASA Goddard MODIS Rapid Response Team
Isaac, a tropical storm that could become Hurricane Isaac by tomorrow (Aug. 28), is barreling across the Gulf of Mexico toward New Orleans, and could hit the city on the anniversary of one of the most devastating storms in living memory.
Hurricane Katrina roared ashore in New Orleans on the morning of Aug. 29, 2005. So what are the chances that Isaac could hit on the same day, seven years later? About 25 percent, said Chris Landsea, the science and operations officer at the National Hurricane Center in Miami.
The latest forecast has Isaac making landfall on Tuesday evening (Aug. 28) — but that could change, Landsea told OurAmazingPlanet.
However, he said, if Isaac does hit on Hurricane Katrina's anniversary, it won't come as a huge surprise. During the peak of hurricane season, a short window of time from mid-August to late October, the Gulf Coast is often hit with a flurry of storms, "so it's not that unusual to have the same place be hit on about the same day," he said.
In addition to timing, geography also plays a role, Landsea said. Regions that protrude into hurricane-prone waters tend to get hit more than those that don't. Just picture Florida, Louisiana, Texas and North Carolina, the four states that top the U.S. list for hurricane strikes — all of them stick out into the ocean more than their neighbors.
On average, hurricanes hit the area around New Orleans about every seven years, according to National Hurricane Center statistics.
Yet it's important to remember there's nothing magic about those numbers, said Robert Henson, a meteorologist who works as a science writer for the University Corporation for Atmospheric Research, in Boulder, Colo. "It's simply a description of the average," he said. "There's no reason why a town couldn't get hit twice even in the same year — or it could be decades."
Both Landsea and Henson emphasized that, aside from similar timing, Isaac and Hurricane Katrina differ in a several significant ways: Isaac's path has it approaching from the southeast, whereas Katrina approached from the south. That may seem like a subtle difference, but it can play a role in how much storm surge a system sends rushing on land, Henson said.
Another difference is that Isaac is expected to become a Category 1 hurricane — a storm with winds that top out at 95 mph (153 kph) — whereas Katrina was a powerful Category 5 hurricane at landfall.
However, even though Isaac is significantly weaker than Katrina, it's a large storm, and is causing significant storm surges. "It's a very large system, so it's pushing a lot of water for its strength," Henson said.
Isaac was named on Aug. 21; satellites have been keeping watch over the storm from above, and hurricane-hunting aircraft have been monitoring it for days now. Late last week, crews sent back some arresting photographs from inside the roiling storm.
Landsea said it's still not possible to know precisely how powerful Isaac will become. Despite all the technological advances in tracking storms, "we're still not very good at making intensity forecasts," he said. "It's still going to be significant, but not to the degree that Katrina was," he added.
Henson agreed, adding that even a storm far smaller than Katrina can still cause a lot of trouble. "Just because it's a Cat 1 doesn't mean it can't be a very destructive storm," he said.