Storms slowing down?

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PTPatrick
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Storms slowing down?

#1 Postby PTPatrick » Mon Sep 17, 2018 11:19 am

With Florence being yet another large sloppy wet system with a big wind field and surge to boot, I have thought a lot about the notion of whether or not storms are changing. It at least seems that we have reached a point where slow moving tropical cyclones are becoming more and more the norm. There is some research that bares that out, showing that over 70 years tropical cyclones have slowed over land worldwide. It looks like as much as 20% for North America. The hypothesis being that as the world warms the patterns in the mid latitudes are becoming more stagnant, jet streams shift, etc.

Regardless of whether you believe in man-made climate change or not it seems that the data at least shows in the recent record that they are slowing down. Whether its a cycle or whatever, it seems to be happening and could have ramifications for how places prepare for storms in the future. Obviously we have always had sloppy wet cyclones that caused floods. So I decided to look state by state at the top 10 tropical cyclone rainfall records. A cursory look through the data shows that throughout the southern states (NC, SC, GA, FL, TN, MS, AL, LA and TX). All but FL and TX have 6 or more of their top 10 tropical rain events in since the 90s. I wasn't able to read the entire Kossin article on the slowdown below but I have found a few different synopsis around the net. It actually makes sense as it seems that they have slowed down the most the higher north of the tropics you go. TX and FL have the most landmass extending toward the tropics so it would follow that for them, and slowdown of storms would have a somewhat smaller effect on the overall record(although obviously Harvey is a good example of what can happen).

Pattern or climate change or whatever, it seems that even a small slowdown of storms, combined with increasing water vapor and heat will make for more and more of these major inland flood events.

I just find it all interesting and curious of others thoughts on the matter. I think anecdotally I have seen it play out it in the area of the northern gulf coast, but I try to not rely on my intuition and limited experience as a 40 year old and focus more on data. I wish we had a longer period of strong hurricane track data. It also seems that slowing down could have ramifications for other aspects of storms besides rainfall...like, could this play a role in what seems like more storms weakening right before landfall (slower forward speed allowing more time for the land mass to interact with them and knock them down a bit)? What role might it have on storm surges (increased period of onshore flow holding surges up higher and longer)? Could we be seeing more ERC's due to increased length of storms travel and thereby more storms expanding in size (and subsequently expanding surges)? Again, I am not saying any of these other things ARE happening, just questioning whether they could be as they might be logical products of storms that move slower.

https://www.nature.com/articles/s41586-018-0158-3
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Re: Storms slowing down?

#2 Postby LarryWx » Mon Sep 17, 2018 12:25 pm

Great stuff, thanks! I was just recently wondering if GW caused TCs to move more slowly on average and figured that determining that wouldn't be easy. I didn't know that a forward speed analysis had already been done.
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Re: Storms slowing down?

#3 Postby Ntxw » Mon Sep 17, 2018 7:18 pm

A quick reanalysis of 500mb easily shows the warming that has happened over the past decades. The expansion of the Hadley Cell can slow down the fast moving mid latitude jets. This effect, in part, can contribute to the breakdown of steering for such storms further north than before. It's not that anomalous ridging hasn't happened in the past, it has happened before, only that the frequency can be greater and the pathway can happen further north than in the past at a bigger number. What is typically sluggish storms are more frequent in the deep tropics, but everything can shift north with the expanding Hadley Cell.
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Re: Storms slowing down?

#4 Postby PTPatrick » Mon Sep 17, 2018 8:22 pm

Yeah I’m convinced... I mean assuming it continues I think storm surges, and tropical and non-tropical floods will continue to challenge where and how we build.

I come from a community that has thrived and existed in the south east corner of Mississippi near the Alabama state line for well over a 100 years. It had some surges over the years 1916, 1947, Camille, to name a few. And it survived its share of bad “dry” storms too like 1926, Elena and Frederic. It has its share of river flooding from regular old storms from time to time too. The combo of hurricane surge and rain seemed to be the Achilles heel though.

In 1997 it freshwater flooded from Danny dumping 2 feet of rain nearby. In 1998 it surge flooded form Georges(higher than Camille, the previous largest) AND then freshwater flooded from Georges’ stall and insane rain. People got really tired by then. Then Katrina came and wiped it out and put water higher than anybody ever knew it could go in the tidal and river areas. People took the hint, most moved on. Many had just gotten back together from georges. There are still some folks out there, mostly the higher spots and the few lucky enough to be on stilts. I suspect we will begin to see that repeated more. I would imagine it has already happened with some of low lying areas around beaumont and port Arthur that got wallopped back to back to back with Rita, Ike and Harvey. And probably some who flooded with Matthew are thinking long and hard as they face the rebuild.
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Re: Storms slowing down?

#5 Postby storm_in_a_teacup » Mon Sep 17, 2018 9:12 pm

What's really weird about the whole "slow moving heavy rain" thing to me is how much it has caused the "typical" severe weather event for Houston to change.
Growing up I remember a whole variety of severe weather events---tornadoes, severe straight-line thunderstorm winds, hailstorms, ice storms, etc.
Nowadays I swear it's just flooding...and more flooding...from tropical moisture (if not an actual tropical system)...over and over again.

The Houston Museum of Natural Science has this little display where kids can go pretend to give a weather forecast in front of a green screen. I remember it used to have tornado, hailstorm, hurricane, and flood options.
After they renovated it, they kept only hurricane and flood.
...So I swear I must not be the only person in Houston who feels like this.

(Not that I miss tornadoes. I'll take floods over tornadoes.)
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