Ike's Massive Damaging Wind Swath

Hurricane Ike made landfall near Galveston, Texas around 2AM on Saturday September 13th, packing wind gusts measured up to 104 mph by a meteorological chase team near Galveston Bay. But its damaging winds were not done there! The figure below shows the swath of wind damage that continued into the night of 14-15 September all the way to the Northeast.

I cannot recall a more extensive swath of damaging winds from any storm! It's not unusual to have wind damage for a few hundred miles inland of a hurricane making landfall. But this swath of damage wound up being about 1600 miles long along the dog-legged path, and about an average of 200 miles wide! Within the swath lies an incredible scene of widespread trees and power lines downed, some falling onto homes and vehicles. Some buildings collapsed or lost roofs from the winds alone. Scenes like the ones below were common across parts of the twelve states within the swath. Some places will be without power for up to two weeks.

Owensboro, Kentucky (submitted by Weather Warrior Terry Whitaker)

From LaRue, OH (submitted by Weather Warrior Dana Greene)

550,000 were left without power in Kentucky, in what officials called the worst disaster since the tornadoes of the Superoutbreak of April 3, 1974 and the largest power outage in state history. Winds gusted to 73 mph at Owensboro, 75 mph at Louisville, and 74 mph at Covington, KY (across the border from Cincinnati). Damage was not confined to falling trees, either. Winds destroyed mobile homes, downed barns, took roofs off homes, factories, and school buildings. Corn fields waiting to be harvested were leveled. Winds gusted to 81 mph at Beaver Falls, PA (north of Pittsburgh); 67 mph at Rochester NY.

The surface weather map below is from 2PM on Saturday Sept 14, when the remnant low pressure center from Ike (L) has merged with a frontal zone and is over northern Indiana. Damaging winds are occurring within the red dashed region along and ahead of the blue cold front. The G65 annotation indicates that winds are gusting to 65 knots (75 mph) at Louisville, KY at this time as the front passes. Winds are gusting to 62 mph (71 mph) simultaneously at Covington, KY (across the river from Cincinnati) at this time, and peaked at 74 mph subsequently, with damage to buildings at each airport. Winds soon gusted to 63 mph at Indianapolis, where a tent collapse at the Speedway resulted in injuries.

Four factors appear to have helped generate the damaging winds. First, the large pressure difference -- or gradient --between Ike's low pressure and the higher pressure outside tends to cause strong winds. It's somewhat like a tube of toothpaste -- the harder you squeeze it the faster it squirts. Second was the presence of strong winds in a "low-level jet" at just a few thousand feet above ground -- up to slightly more than 80 mph across the region. The third factor was unusually warm air aloft that inhibited instability and clouds and allowed considerable sunshine. That sunshine allowed temperatures to climb into the 80s and induce a lot of stirring in those lowest few thousand feet -- with warm bubbles rising up and bubbles from aloft being pushed down to the ground bearing damaging wind gusts from within that low-level jet. This occurred ahead of the cold front. A fourth factor involved the front, and the change from falling pressures ahead of it to rising pressures behind it.

That latter factor, involving the pattern of pressure rises and falls and the cold front, merits a bit more discussion. The figure below illustrates the pressure fall and rise pattern as Ike's low-pressure system moved across Arkansas.

Ike's 6-hour pressure-change pattern (courtesy of National Weather Service, Little Rock, AR)

Ahead of Ike's low pressure center, pressures fell up to 11 mb (-11) as Ike approached, then rose up to 12 mb (millibars) in regions to the southwest of Ike's low-pressure center after Ike passed. There is a tendency for air to be pushed/pulled or "sucked" down cold fronts from the pressure rise areas toward the pressure fall areas. This probably contributed to the strong southwest-to-northeast damaging winds in this storm -- as depicted in the "very windy" zone on the diagram. If you want throw a big word out to impress or harass your friends, this is called the "isallobaric effect."

This is pretty involved meteorology -- which a few of you might find of interest. But the bottom line for all of us is that Ike has left a terrible mess across a wide area. Homeowners and businesses are trying to get their lives and livelihoods back to normal, communities are trying to clear roads and restore power, farmers are trying to harvest their flattened crops, and -- for the rest of us - our hearts go out to them.