Last week, a story about ‘wind fingerprints’ in The Washington Post caught my eye. It purported to show the difference between Ida and Katrina. The story by Bonnie Berkowitz and Laris Karklis starts with this teaser: “Ida hit Louisiana with faster winds than Katrina, but a hurricane’s category number is just part of what makes each storm unique — and uniquely destructive.” I was hooked.
Factors in Fingerprinting Storms
“Ida struck Louisiana on Aug. 29 as a strong Category 4 on the Saffir-Simpson scale, with maximum winds of about 150 mph — much higher than the maximum winds of 125 mph from Katrina, a Category 3,” say the authors.
However, the wind speed is just part of the picture. To get the big picture, one must also consider:
- Breadth of the wind field
- Wind direction
- Total energy contained in the storm
- Forward motion
- Angle at which it struck the coastline
- Proximity to population centers
- And more.
The story quotes Michael Kozar, a meteorologist who models storms for risk-analysis company RMS. Says Kozar, each wind field is like a fingerprint.
Examples of Wind Fingerprint Differences
“A very large storm with moderate winds may contain more integrated kinetic energy than an intense but small storm, and it may create havoc for people on land in a different way,” says the story.
The story goes into great detail comparing Ida to Katrina. Ida packed higher winds (150 vs. 125 mph peaks). But Katrina packed more energy – 116 terajoules vs. 47 for Ida. By comparison, Superstorm Sandy in 2012 had an estimated 330 terajoules of energy.
A terajoule is so large, it’s hard to find an analogy that puts it in perspective for most people. But scientists estimate that the atomic bomb over Hiroshima released about 63 terajoules of energy – slightly more than Ida, but a little less than half of Katrina.
RMS estimates the smaller punch of Ida was due in part to the shorter time it was able to gather steam, so to speak, over open water. Ida gained full strength just hours before landfall. But Katrina churned over the open Gulf for three days before slamming into Louisiana. It grew much larger, in fact, about twice as large.
RMS also explained how Katrina came in east of Lake Pontchartrain, while Ida came in to the west. With the counter-clockwise rotation of low pressure systems in the northern hemisphere, that meant Katrina pushed water toward New Orleans and Ida pushed water away.
The forward speed of a storm can make a huge difference in the types of damage it causes compared to its rotational speed. Category 4 Harvey, for instance, stalled over Houston for days, dropping torrential rains. But Category 5 Hurricane Andrew ripped through south Florida in hours. Harvey flooded homes. Andrew tore them apart.
This article gives you both insights and food for thought that can help you prepare better for the next storm. It’s highly recommended reading.
Posted by Bob Rehak on 9/7/2021 based on a story by Bonnie Berkowitz and Laris Karklis in The Washington Post and data from RMS
1470 Days since Hurricane Harvey