The National Hurricane Center issued a special advisory a half-hour ago, indicating that Hurricane Katrina has rapidly strengthened into a Category 2 hurricane with maximum sustained winds of 100 mph, and further intensification seems inevitable:
Given the rapid improvement in the inner core structure and the sharp pressure drop…rapid intensification seems likely for the next 12 hours or so. Afterwards…steady intensification to near category four strength by 72 hours appears to be in order given the very warm Gulf waters beneath the hurricane and the vertical shear forecast to decrease to less than 10 kt by 48 hours.
So where will this soon-to-be-a-monster hurricane go? The computer models are all over the map (more here). According to the 10:00 AM discussion:
The NOGAPS and GFDN models have made a large jump to the west over Louisiana…whereas the majority of the NHC models take Katrina inland over the northeast Gulf Coast [i.e., Alabama or the Florida panhandle]. The official forecast track remains in the right portion of the model guidance envelope.
I’m not sure why Stewart (the NHC forecaster) said the GFDN jumped west, it had already been showing a Louisana landfall (see the
12Z (8 AM EDT) model guidance from yesterday). As you can see from the graphic, it was an extreme outlier at the time. However, models are shifting west right now, so it isn’t as much of an outlier as it has been.
Question for you, Charles. If a Category 3 or 4 hurricane hits New Orleans from the south (as opposed to from the east-southeast, which I understand to be the worst-case scenario), crossing some land (the Mississippi Delta, I guess?) on its way up, is that likely to cause the doomsday scenario envisioned by disaster planners (flooding the bowl, etc.)?
Also… would crossing the Mississippi Delta really weaken a hurricane much before hitting New Orleans… or would that be sort of like the Everglades?
I don’t believe New Orleans would get the catastrophic storm surge if a hurricane were to come up directly underneath it from due south. It would still however, be an extremely ugly flood situation, especially if the storm were slow moving (
If my thinking is correct, it would be slightly worse for the storm to come in from due south just west of N.O., as that would put the whole of the city in the northeast quadrant.
Betsy of ‘65 gives us some kind of an idea of the possibilities. Despite being ore than 50 miles to the southwest of N.O., it still flooded the city.
As far as dissipative effects, I don’t think the ‘land’ to the south of New Orleans would amount to much, but that is speculation on my part. I am not familiar with it and don’t know how it compares to the area where Andrew went ashore (it went from category three hurricane to tropical storm in 12 hours).
(not sure why most of my comments got cut off, sorry for the extra comment)
I just re-read the Times-Picayunespecial report, and it includes this passage:
“The worst case is a hurricane moving in from due south of the city,” said [LSU engineer Joseph] Suhayda, who has developed a computer simulation of the flooding from such a storm. On that track, winds on the outer edges of a huge storm system would be pushing water in Breton Sound and west of the Chandeleur Islands into the St. Bernard marshes and then Lake Pontchartrain for two days before landfall.
“Water is literally pumped into Lake Pontchartrain,” Suhayda said. “It will try to flow through any gaps, and that means the Inner Harbor Navigation Canal (which is connected to Breton Sound by the Mississippi River-Gulf Outlet) and the Chef Menteur and the Rigolets passes.
“So now the lake is 5 to 8 feet higher than normal, and we’re talking about a lake that’s only 15 or 20 feet deep, so you’re adding a third to a half as much water to the lake,” Suhayda said. As the eye of the hurricane moves north, next to New Orleans but just to the east, the winds over the lake switch around to come from the north.
“As the eye impacts the Mississippi coastline, the winds are now blowing south across the lake, maybe at 50, 80, 100 mph, and all that water starts to move south,” he said. “It’s moving like a big army advancing toward the lake’s hurricane-protection system. And then the winds themselves are generating waves, 5 to 10 feet high, on top of all that water. They’ll be breaking and crashing along the sea wall.”
Soon waves will start breaking over the levee.
“All of a sudden you’ll start seeing flowing water. It’ll look like a weir, water just pouring over the top,” Suhayda said. The water will flood the lakefront, filling up low-lying areas first, and continue its march south toward the river. There would be no stopping or slowing it; pumping systems would be overwhelmed and submerged in a matter of hours.
“Another scenario is that some part of the levee would fail,” Suhayda said. “It’s not something that’s expected. But erosion occurs, and as levees broke, the break will get wider and wider. The water will flow through the city and stop only when it reaches the next higher thing. The most continuous barrier is the south levee, along the river. That’s 25 feet high, so you’ll see the water pile up on the river levee.”
I don’t want thousands of people to die, but I do want to see what happens when a powerful hurricane strikes New Orleans. I won’t pray for the hurricane to hit New Orleans, but I won’t pray for it to miss, either. ;-)
I do want to see what happens when a powerful hurricane strikes New Orleans
I’ll admit that, as a news and weather junkie, and a general “master of disaster” (as my dad used to call me), I would be most interested to see it happen — but I will continue to root, hope and pray against it, because the thousands of deaths are a pretty much inevitable side effect.
One could argue, of course, that it’s only a matter of time, and thus one could even make the case that “better now than later,” assuming New Orleans’s population is growing and likely to continue to grow. But the counterargument to that is, give them time and perhaps they’ll come up with a better plan to save lives when The Big One finally comes. Maybe that’s a fool’s hope, but it’s a hope. Either way, I will refrain from making the case I mentioned above, and will continue to hope Katrina turns east (or well west).
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August 26th, 2005 at 12:18:24 pm
I’m not sure why Stewart (the NHC forecaster) said the GFDN jumped west, it had already been showing a Louisana landfall (see the
12Z (8 AM EDT) model guidance from yesterday). As you can see from the graphic, it was an extreme outlier at the time. However, models are shifting west right now, so it isn’t as much of an outlier as it has been.
August 26th, 2005 at 12:44:34 pm
Question for you, Charles. If a Category 3 or 4 hurricane hits New Orleans from the south (as opposed to from the east-southeast, which I understand to be the worst-case scenario), crossing some land (the Mississippi Delta, I guess?) on its way up, is that likely to cause the doomsday scenario envisioned by disaster planners (flooding the bowl, etc.)?
Also… would crossing the Mississippi Delta really weaken a hurricane much before hitting New Orleans… or would that be sort of like the Everglades?
August 26th, 2005 at 3:07:38 pm
I don’t believe New Orleans would get the catastrophic storm surge if a hurricane were to come up directly underneath it from due south. It would still however, be an extremely ugly flood situation, especially if the storm were slow moving (
August 26th, 2005 at 3:09:54 pm
, i.e. less than 10 mph.
If my thinking is correct, it would be slightly worse for the storm to come in from due south just west of N.O., as that would put the whole of the city in the northeast quadrant.
Betsy of ‘65 gives us some kind of an idea of the possibilities. Despite being ore than 50 miles to the southwest of N.O., it still flooded the city.
As far as dissipative effects, I don’t think the ‘land’ to the south of New Orleans would amount to much, but that is speculation on my part. I am not familiar with it and don’t know how it compares to the area where Andrew went ashore (it went from category three hurricane to tropical storm in 12 hours).
(not sure why most of my comments got cut off, sorry for the extra comment)
August 26th, 2005 at 3:51:40 pm
Charles,
Thanks. :)
I just re-read the Times-Picayune special report, and it includes this passage:
“The worst case is a hurricane moving in from due south of the city,” said [LSU engineer Joseph] Suhayda, who has developed a computer simulation of the flooding from such a storm. On that track, winds on the outer edges of a huge storm system would be pushing water in Breton Sound and west of the Chandeleur Islands into the St. Bernard marshes and then Lake Pontchartrain for two days before landfall.
“Water is literally pumped into Lake Pontchartrain,” Suhayda said. “It will try to flow through any gaps, and that means the Inner Harbor Navigation Canal (which is connected to Breton Sound by the Mississippi River-Gulf Outlet) and the Chef Menteur and the Rigolets passes.
“So now the lake is 5 to 8 feet higher than normal, and we’re talking about a lake that’s only 15 or 20 feet deep, so you’re adding a third to a half as much water to the lake,” Suhayda said. As the eye of the hurricane moves north, next to New Orleans but just to the east, the winds over the lake switch around to come from the north.
“As the eye impacts the Mississippi coastline, the winds are now blowing south across the lake, maybe at 50, 80, 100 mph, and all that water starts to move south,” he said. “It’s moving like a big army advancing toward the lake’s hurricane-protection system. And then the winds themselves are generating waves, 5 to 10 feet high, on top of all that water. They’ll be breaking and crashing along the sea wall.”
Soon waves will start breaking over the levee.
“All of a sudden you’ll start seeing flowing water. It’ll look like a weir, water just pouring over the top,” Suhayda said. The water will flood the lakefront, filling up low-lying areas first, and continue its march south toward the river. There would be no stopping or slowing it; pumping systems would be overwhelmed and submerged in a matter of hours.
“Another scenario is that some part of the levee would fail,” Suhayda said. “It’s not something that’s expected. But erosion occurs, and as levees broke, the break will get wider and wider. The water will flow through the city and stop only when it reaches the next higher thing. The most continuous barrier is the south levee, along the river. That’s 25 feet high, so you’ll see the water pile up on the river levee.”
August 26th, 2005 at 4:17:45 pm
I don’t want thousands of people to die, but I do want to see what happens when a powerful hurricane strikes New Orleans. I won’t pray for the hurricane to hit New Orleans, but I won’t pray for it to miss, either. ;-)
August 26th, 2005 at 4:59:52 pm
I do want to see what happens when a powerful hurricane strikes New Orleans
I’ll admit that, as a news and weather junkie, and a general “master of disaster” (as my dad used to call me), I would be most interested to see it happen — but I will continue to root, hope and pray against it, because the thousands of deaths are a pretty much inevitable side effect.
One could argue, of course, that it’s only a matter of time, and thus one could even make the case that “better now than later,” assuming New Orleans’s population is growing and likely to continue to grow. But the counterargument to that is, give them time and perhaps they’ll come up with a better plan to save lives when The Big One finally comes. Maybe that’s a fool’s hope, but it’s a hope. Either way, I will refrain from making the case I mentioned above, and will continue to hope Katrina turns east (or well west).