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Tropical Hurricane Ida

DadOfJax said:
Carolinians dying to be relevant in regards to Ida….let them talk…mute works great too!
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Honestly I don’t wish anything on the Carolinas especially the mountains. The deaths in Haywood county do to Fred is devastating really don’t need Ida


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Brent said:
Why do mets do this? The Cat 3 point is inland and not to mention there's actually a chance at a 5
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It’s not the mets fault it’s the CAT system we should allow storm surge and rain factor into being a CAT 5 not just the wind speed which often lessen upon land friction processes.
 
BirdManDoomW said:
It’s not the mets fault it’s the CAT system we should allow storm surge and rain factor into being a CAT 5 not just the wind speed which often lessen upon land friction processes.
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The category system based on wind is a pretty good indicator of surge, but surge variates based on geography. That is way too random a system to base hurricane designations, and rainfall is more variable than surge cause of fronts and ridges. Wind would have been fine indicator of surge in New Orleans, and the NHC could have realized this potential 36 hours ago. There was a chance this could go to Cat 5 at that point, and now it looks more likely Ida is a Category 5 than 3 at landfall (4 being most likely).
 
lexxnchloe said:
I just read up on Betsy. It was at 942mb when it made landfall. The good news is Ida is alot weaker.
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Ida will likely never be as large as the mature, Cape Verde cane that Betsy was, but it will take some good fortune if Ida isn't below 942mB at landfall.
 
Just IMO, but our mid Atlantic “thang” is becoming ever so more interesting with its influence on Ida and her track. They are far enough apart but for some reason model guidance hints at some interactions between this unknown feature @Webberweather53 C479AF51-12E2-4BA6-9537-C75812280CD2.jpeg
 
I haven’t followed closely but some are saying former Hurricane Henri is coming back from the dead in a backdoor fashion. I don’t think so, but none the less that’s interesting when both are getting closer together
 
wxdaniel said:
Could I quote this on my site with your name?
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Let's keep it a SouthernWX exclusive ?

Chazwin said:
I’m not sure I would say for definite that surge is “not allowed” inside the city. Though I do pray that you’re right. The fact is this storm appears to be coming in at an angle that is probably the worst case scenario for New Orleans. While I do think the levees will hold and not break, I’m concerned we may see water going over the top of the levees if this thing reaches strong cat. 4/5 at landfall
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Let me explain what I mean about "not allowed inside the city." Imagine the major outfall canals as well as the Industrial canal/Intracoastal as fingers of water penetrating deep into the city. Pre-Katrina, surge was allowed to freely flow from the lake and MRGO back in to these areas. The only thing protecting the city were essentially the floodwalls and levees along the outfall canals. It's totally different now. Seawalls and pump stations have been built where the outfall canals flow in to the lake. The gates are closed and pumps switched on when the surge starts coming in to the lake. On the Industrial Canal/Intracoastal/MRGO side of the city, you now have the Lake Borgne Surge Barrier as well as the closure of MRGO to stop water from coming into the Industrial Canal area.

There are still possible failures of the outfall canal walls, but that would be because of pressure from rain pumped in to the canals from the city and not from surge. That scenario would require the failure of major outfall canal pumps at the lake and their backups. It's unlikely, but as before, more than a zero probability.

We learned a lot from the Dutch. Things such as the Lake Borgne Surge Barrier were ideas drawn up during the first Dutch Dialogues. Why have many miles of defense when you can concentrate your defense in one area? It makes so much sense, and you wonder why we never did it prior to Katrina, but like the Dutch, it took a disaster to recallibrate our thinking. The Dutch didn't start their Delta Works program until the North Sea Flood of 1953. It took us experiencing Katrina to start our version of Delta Works.
 
Nash_LSU said:
Let's keep it a SouthernWX exclusive ?



Let me explain what I mean about "not allowed inside the city." Imagine the major outfall canals as well as the Industrial canal/Intracoastal as fingers of water penetrating deep into the city. Pre-Katrina, surge was allowed to freely flow from the lake and MRGO back in to these areas. The only thing protecting the city were essentially the floodwalls and levees along the outfall canals. It's totally different now. Seawalls and pump stations have been built where the outfall canals flow in to the lake. The gates are closed and pumps switched on when the surge starts coming in to the lake. On the Industrial Canal/Intracoastal/MRGO side of the city, you now have the Lake Borgne Surge Barrier as well as the closure of MRGO to stop water from coming into the Industrial Canal area.

There are still possible failures of the outfall canal walls, but that would be because of pressure from rain pumped in to the canals from the city and not from surge. That scenario would require the failure of major outfall canal pumps at the lake and their backups. It's unlikely, but as before, more than a zero probability.

We learned a lot from the Dutch. Things such as the Lake Borgne Surge Barrier were ideas drawn up during the first Dutch Dialogues. Why have many miles of defense when you can concentrate your defense in one area? It makes so much sense, and you wonder why we never did it prior to Katrina, but like the Dutch, it took a disaster to recallibrate our thinking. The Dutch didn't start their Delta Works program until the North Sea Flood of 1953. It took us experiencing Katrina to start our version of Delta Works.
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Thanks for the insight. Have you seen any estimates on the return period for a levee overtopping event. That has always been the top headline for a deadly disaster in NO. I've heard they're comfortable the new system is designed for a 100 yr storm; I was just curious what it's capable of handling.
 
Nash_LSU said:
I think it's prudent to sound an alarm for New Orleans and for people to get out, but New Orleans is in a much better place than they were 16 years ago as far as surge protection is concerned. The surge protection system is very different than it was for Katrina. It's certainly not immune to surge, but it is much better protected. There are multiple lines of defense to stop surge, and surge is no longer allowed "inside" the city like it was before.

The city as a whole has not sunk an additional two feet. Some areas of New Orleans East and the Lower Ninth/St Bernard parish line have subsided about half that, but on a whole, the city sits on average a couple inches further down than before, and that average is skewed because of the extreme outliers. You'll see news stories mentioning rates of 2-3 inches per year, but that's for small portions of the city.

IMO, the major threat to the city these days is wind and rainfall within the levee systems. I think rain is the biggest and most likely threat. I have a very intimate knowledge of the storwater infrastructure of the city, and I have a little less than zero faith in it. The surge protection and outfall canal pumps are top of the line, but past that it gets scary quickly. An afternoon thunderstorm is enough to flood certain neighborhoods. If a train of tropical moisture sets up in the right spot, good luck. The system is theoretically able to handle 1" of rain in the first hour and a half an inch for every hour after that. At some point, due to crappy pipes and catch basins, the streets begin to act as conveyance. The city even uses 6" of stormwater storage capacity for all the streets in their calculations. It's mind-bogglingly idiotic, but whatever.

There is a possible scenario where a slow moving system keeps surge way up and dumps massive amounts of rain in the city. This would kind of fill up the areas between the lines of defense and outside the lines of defense, and once that area is filled up, it would flow back in to the city. It's a low probability scenario, but not a zero probability. A slower storm coming from a more SE angle increases the probability.

All that said, we thought the city was safe last time. It wasn't. We think the city is safe this time. We all hope it is as Ida is looking like no joke for SELA.

Source:
<-- worked on flood control for a decade in New Orleans following Katrina. I am by now means the end all be all authority, but I do have a pretty in depth knowledge of the water systems in the metro Nola area, especially the east bank portions. It has been six years since I worked in the area, so some of my information could be out-dated.
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Surge can still get inside the city unfortunately with extra stress going to be put on working levees as several of the drainage pumps are down (apparently it's a running joke for residents that a majority of them aren't working half the time (sad really)). If I was a resident there, none of this exactly instills confidence, esp when a comparable or stronger storm at landfall (remember Katrina weakened to a 3) is on the way. The lack of natural marshland to buffer the city from the Gulf of Mexico to the SE is also a major concern and arguably makes the city much more vulnerable despite the man-made barricades that have been put up. There will be much less in the way than 15 years ago to stop the water from the SE. Still a legitimate possibility this storm too passes to the east of the city and puts pressure from the north via Lake Pontchartrain
 
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