Helene’s size shocked me but the storm surge for Katrina was unusually extreme. It was a well organized Category 5 and then weakened to a strong 3 right before landfall.
To compare with Helene, which was similar in terms of (east to west) diameter but covered much more area overall, with category 4 winds at landfall: the Weather Channel was making a big deal out of the 8ft storm surges. During Katrina, the Mississippi Gulf Coast had a 28 foot storm surge. (The Miss. Gulf Coast isn’t that geographically different from the Fla. big bend region but that plays a role too.)
Helene’s unusual movement speed kept it strong very far inland and caused massive issues in places that rarely see tropical weather. Harvey was the opposite: it stalled over Houston and dumped days of rain on a major metropolis.
I wish we could update the Saffir Simpson scale to something that takes into account more variables. There are other measurements but no storm is identical in terms of damage potential. A category 5 can not even make landfall whereas something like Hurricane Sandy was a category 1 (or equivalent since it wasn’t technically still a hurricane) when it hit NYC and caused massive damage and flooded subway systems. Sometimes, a storm hitting a place that isn’t used to them can knock over all the trees or flood rivers while a similar storm would be nothing to Miami or New Orleans.
Helene is more deadly than Katrina if you don’t count the deaths after the boat broke the levee that was well beyond its lifespan in New Orleans, which you shouldn’t since that was a 100% fixable issue that was not taken care of.
We always say Katrina was a man-made disaster. I worry with climate change, that other places will be testing their infrastructure. Katrina should have been the canary in the coal mine and a lot of people just said, “Don’t live below sea level.” Old river damns can break just as easily as neglected levees.
It was definitely a man-made disaster when it came to New Orleans. I made this analogy to someone else: if lightning strikes a skyscraper and the skyscraper burns down and kills everyone inside due to a lack of a sprinkler system, is that really death by a natural cause? I would say it’s death by gross incompetence.
What surprised me most about Helene was the ground speed. I don’t remember seeing any hurricane make landfall in the US moving at over 20mph. As a casual observer I have anyways seen 12 mph as a quick storm and 6 mph as slow.
