Why Did We Get a Monster Hurricane in the Gulf?

[billroper]

filkertom points out that there are some idiots who think that Hurricane Katrina was the Wrath of God directed at a sinful city. Other folks, including officials of foreign governments, have pointed at global warming as the cause. I'm sure we'll hear a lot of theories go by in the coming weeks and months, most of them -- in my opinion -- not being worth the paper they're printed on or the electrons that are used to distribute them.

It appears that hurricane frequency and intensity is controlled more by some long-term cycle that we don't understand than by global warming. We had a bunch of hurricanes in the 50s, then a long quiet cycle while people built a bunch of stuff on the coastline, followed by another active cycle starting around 1995.

My personal (and slightly educated) opinion on why Katrina developed in such a nasty way follows:

We started out with a very active hurricane season this year. Then, we went through a substantial period -- about a month -- where conditions were temporarily unfavorable for hurricane formation. We had Harvey and Irene in the Atlantic, neither of which were any great shakes, followed by Jose which blew up and immediately down as it hit the Yucatan. That wasn't much activity for August.

If Katrina had followed a normal path, it would have crossed Florida from east to west and curved north, pretty much following the coast. It never would have gotten very strong and would have dumped a lot of rain and done a little bit of damage.

Instead, Katrina was blocked and veered south across the Everglades. It didn't lose much strength crossing the wetlands and it got into the Gulf of Mexico, which was very warm because there hadn't been any tropical cyclones churning it for quite some time. The storm moved really slowly, still blocked by the atmospheric phenomenon that had forced it south, giving it plenty of time to intensify.

Once it got around the blocking event, it could recurve normally, but now it was a Category 5 storm aimed at New Orleans and the central Gulf Coast.

So we got a catastrophic storm instead of a couple of smaller ones.

Not Wrath of God. Not global warming. Just some bad luck capped off by a big blocking area of what I assume was high pressure. (But I'm an amateur meteorologist. We don't get the good maps.)

Comments

[sdorn.livejournal.com]

That looks to be the consensus on Katrina's intensification. I agree that there is no evidence that global climate change (apart from the hurricane activity cycles) affects hurricane frequency. And the one report I've heard of about intensity is just that—one report.

A few other things of note:

• The very warm waters of the central Gulf over the weekend (which probably don't exist anymore after Katrina's churning) helped fuel Katrina
  
• I've heard something that a (very large) mass of dry air from the midwest sucked a bit of energy from Katrina and pushed it eastward just before landfall.

[billroper]

Right on both points. The central Gulf had been quiet and had plenty of chance to heat up before Katrina used the heat for fuel.

A large trough of dry air moved out from Oklahoma / Texas shortly before landfall. You could see Katrina losing steam on its westward side as a result if you were watching the radar.

[backrubbear.livejournal.com]

The question then becomes, was the warm air front pushing from the North a normal expected weather pattern for this time of year?

[billroper]

Cool front, actually. It's not a great surprise that we'd be getting some cool air moving down from Canada about now.

[backrubbear.livejournal.com]

So, what's different this year from previous years?

[billroper]

We're in what is an "active" hurricane year, but during most of August, conditions weren't favorable for a storm to blow up to even tropical storm status. This apparently has to do with high altitude winds taking the top off of developing tropical systems and keeping them from intensifying.

So nothing came churning through the Gulf until it was nice and warm. Katrina blew up around Bermuda (which is, I believe, fairly unusual), couldn't go north because it was blocked by Atlantic high pressure, got into the Gulf intact, and found a lot of warm water that no other system had gotten to first. And if a storm had gotten there earlier, it wouldn't have been as intense, because there would have been less time for the ocean to heat up.

[backrubbear.livejournal.com]

Sounds like we need a way to disperse that sort of accumulated energy before it's opportunistically picked up.

[faxpaladin.livejournal.com]

(cynicalsarcasm)But don't you realize God put the blocking event there?(/cynicalsarcasm)

The God's Wrath hypothesis strikes me as a particularly sick variation on the old joke about the pastor warning his golfing partner who keeps spouting obscenities when he misses putts. Suddenly lightning strikes the pastor, and a sepulchral voice starts spouting obscenities...

But I suppose God decided to take out the Mississippi casinos as well in a bank shot...

[shsilver.livejournal.com]

But according to Columbia Christians for Life, it was God's way of punishing Louisiana for having 10 abortion clinics. Of course, later, they said it was to prevent Southern Decadence, an annual gay-themed bash that was scheduled for Labor Day weekend in New Orleans.

[billroper]

Yes, and if it was in 1988, the SMOFS list would have argued that the hurricane occurred to prevent Nolacon.

[pheltzer.livejournal.com]

I have to quibble on one point. The storm did lose considerable strength going across FL. Immediately after crossing FL it was downgraded back to a Tropical Storm. It regained strength again rather rapidly as it went to the warmer waters of the Gulf.

And the God's wrath plan clearly can't be right... and stay with me on this one the logic is staggering. Look at where all the major damage was Louisiana, Mississippi, Alabama, and Florida. Those states all voted for George W. in the last two elections. And clearly W. is God's 'Man'. So why would God devastate some of W's strongest supporters. Just doesn't wash. [End Sarcasm]

[billroper]

While Katrina did lose strength crossing Florida, the difference between a Category 1 hurricane and a top-end tropical storm is literally a mile per hour of sustained wind speed. She never became disorganized in any sense during the Florida transit, partly due to being over the Everglades and partly due to it being about the shortest path she could take over the state. When Katrina reached the Gulf, she was well positioned to regain strength, because the storm still "had all its parts".

[mplsfish.livejournal.com]

I have been informed there was a call for mass simultanious meditation to try to push the storm east in order to bypass New Orleans. (don't know how I missed the memo) They are taking credit for the weakening.

Hurricane cycles

[rinioth.livejournal.com]

Thinking on the 50 year (ish) cycle, were there more storms in the early 1900s? How far back do weather records go for that part of the USA?

Re: Hurricane cycles

[filkergem.livejournal.com]

What I'm told is the most deadly hurricane (possibly storm of any kind) in the US hit Galveston, Texas in 1900. Multiple thousands of people were killed in it - I'd heard 8-12,000, though http://www.1900storm.com/ says "more than 6,000". So, there was at least one major one in that time frame.

Re: Hurricane cycles

[pheltzer.livejournal.com]

There are very few accurate records of Hurricanes back before the 1920's. I know as far as Florida is concerned they pretty much begin with the Hurricane of 1926 which basically wiped out South Florida and the Keys. There has also been some scientific analysis tying Hurricane cycles to Sun Spot cycles. Observationally it appears that we hit a rough patch of Hurricanes after a long cycle of sun spots.

Re: Hurricane cycles

[billroper]

Here's a chart of hurricanes that made landfall in the U.S. by decade going back to the 1850s.