Tag Archive for: Ida

‘Wind Fingerprints’: Scientists Dissect What Accounts for the Destructiveness of Different Storms

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
  • Track
  • 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.

“Each wind fingerprint is unique to the storm, and it is why each storm produces a unique amount of loss and has unique impacts.”

Michael Kozar, RMS

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.

Relative size of wind fields estimated by risk-analysis firm RMS. Katrina more than doubled Ida’s diameter.

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

Cat-4 Ida Hits Louisiana with 150 MPH Winds and 12-Foot Storm Surge

The forecasts turned out to be accurate. According to Jeff Lindner, Harris County meteorologist, “Hurricane Ida made landfall at 11:55 am today at Port Fourchon, LA with sustained winds of 150 mph and a central pressure of 930mb.” Storm surge at the coast is 12 feet above ground level.

Image from RadarScope Pro from KLIX New Orleans Radar.

Wind Reports

Although Ida’s extreme winds are confined to the inner eyewall, aircraft data indicate that hurricane-force winds extend outward about 45 nautical miles to the northeast of the center. Based on buoy data the tropical-storm-force wind field extends outward about 130 nautical miles northeast of the center. Here are some readings as of 1PM Sunday 8/29/2021.

Grand Isle: 146mph (unconfirmed)

Port Fourchon: 153mph (unconfirmed ship)

West Delta Oil Platform: 149mph (elevated just off the coast)

Wind Forecast

For those with friends and relatives in Louisiana who did not evacuate, the National Weather Service predicts that winds will remain over 100 mph for the next 12 hours, decrease to 60 within 24 hours, the drop to 35 mph within 36 hours. Damaging wind gusts are expected in metropolitan New Orleans.

Misery Not Yet Over

The storm should follow this track.

Ida’s track will take it over portions of Tennessee severely damaged by flash flooding last weekend.
Large portions of SE Louisiana could see 15-20 inches of rain.
Most of the state has a moderate to high risk of flash flooding.

“Ida will continue to produce heavy rainfall today through Monday across the central Gulf Coast from southeast Louisiana, coastal Mississippi, and far southwestern Alabama, resulting in considerable to life-threatening flash and urban flooding and significant river flooding impacts,” says the NHC. “As Ida moves inland, significant flooding impacts are possible across portions of the Lower Mississippi, Tennessee Valley, Upper Ohio Valley, Central Appalachians and the Mid-Atlantic through Wednesday.”

Storm Surge

Storm surge has deadly potential along the coast. NHC calls it, “Extremely life-threatening.” And they say, “Overtopping of local levees … is possible.”

Surge recorded so far:

East Bank Mississippi River (South of New Orleans): 12.15ft (AGL)

Shell Beach: 7.51ft (AGL)

Grand Isle: 6-8 ft (AGL)

Thus far all federal levee protection and floodgates/walls are preforming as expected. Catastrophic impacts will continue inland over southeast Louisiana into tonight.

I was planning on doing a 4-year retrospective on Harvey today, but will postpone that out of deference to the suffering east of us. Thoughts and prayers for our neighbors who provided so much help in our hour of need.

Posted by Bob Rehak on 8/29/2021 based on information from NHC and HCFCD

1161 Days since Hurricane Harvey