ATL: ISAAC - Post-Tropical - Discussion

[Buck]

Correct me if I'm wrong, but doesn't the Tangipahoa River flow into Lake Pontchartrain, which is already quite full of water?

Indeed it does.

[gboudx]

Miss. officials to breach Isaac-damaged dam on Tangipahoa River

"To prevent flooding from an uncontrolled breach, Mississippi officials are planning to breach the dam on their own to relieve water pressure. Such a plan would flood forested areas of Pike County with 4 feet of water but spare homes and residents in Tangipahoa."

"Jindal said flooding from a dam failure would be as bad as river flooding in the area in 1983 and 1992, when water levels rose to between 17.2 feet and 17.5 feet. It was not immediately clear how far above flood stage those levels are.

It is not clear when a controlled breach would occur or how long the dam can hold before it fails."

[rtd2]

I saw where Jeff Masters said that 'Category 1' isn't a good way to label Isaac... sure, that's what category his winds fell under, but his impact is much greater than most category one storms we've seen.

This is a sore subject around here. But i have felt too much infuses is put on winds and cat 1,2,ect just like we talked about after Katrina that was officially a cat 3 with a 920mb pressure . That said after Isaac I doubt you will here the the "oh its just a cat 1" phrase anytime soon"

[WeatherGuesser]

Funny how the thread on an active storm that still poses a significant threat to many is all but abandoned for threads on things that may never amount to anything.

[gboudx]

Funny how the thread on an active storm that still poses a significant threat to many is all but abandoned for threads on things that may never amount to anything.

It happens all the time. It's the "thrill of the chase" mentality where posters will follow a storm until it makes landfall. Usually only the true diehards stick around and people who are affected. Others, like myself, only follow if it affects a specific area. For example, I won't follow a storm that will recurve out to sea, or landfall on the east coast. Honestly, I wouldn't have followed Isaac so much had it made landfall east of Gulfport.

[southerngale]

I saw where Jeff Masters said that 'Category 1' isn't a good way to label Isaac... sure, that's what category his winds fell under, but his impact is much greater than most category one storms we've seen.

I am not crazy about the whole category thing because I think the lower categories make people too complacent, but I haven't exactly come up with a better system, either. Tropical Storm Allison also proved that you don't even need a category to cause horrific damage and death.

[HurricaneQueen]

I'm still following Isaac both on the board and TWC day and night and I am in SW FL with no contacts on the northern gulf shores. My heart is breaking for all the devastation and lives destroyed once again.

[cigtyme]

Thanks HQ, Power is on finally ! Work tomorrow, and curfew is lifted!!

[Houstonia]

I saw where Jeff Masters said that 'Category 1' isn't a good way to label Isaac... sure, that's what category his winds fell under, but his impact is much greater than most category one storms we've seen.

I am not crazy about the whole category thing because I think the lower categories make people too complacent, but I haven't exactly come up with a better system, either. Tropical Storm Allison also proved that you don't even need a category to cause horrific damage and death.

Harris County Flood Control District's Met Jeff Lindner also vents his frustration in this morning's Isaac update:

Isaac continues to bring flooding rainfall and storm surge to the LA and MS coast.

Overnight strong SSW winds have surged the waters within Lake Pontchartrain northward away from New Orleans and into the northern shore of the lake. Severe storm surge flooding of 5-7 feet is currently in progress from the western side of the lake to the eastern side of the lake including the cities of Slidell, Mandeville, and LaPlace. Early this morning a levee was breached near a pump station in the City of Slidell and while the pump station continues to operate, it cannot keep out with the influx of water and portions of the city are now flooding with 3-5 feet of water…all locations in the city at an elevation below 9 ft will be subject to flooding. Overtopping also occurred late yesterday afternoon in St John the Baptist Parish and around LaPlace where at least 1000 residents are still being rescues from their rooftops.

Initial water level readings on the west side of Lake Pontchartrain include that record high storm surge levels may have been produced and flooding west of New Orleans and on the north shore of the lake is equal if not greater than hurricane Katrina and hurricane Gustav. These high water levels are a function of the storm track, as Isaac passed to the south and then west of Lake Pontchartrain allowing a continuous feed of sea water on SE winds into the lake. Hurricane Katrina passed just east of the lake initially pushing sea water in from the east, then sloshing that surge southward on the west side of the eye against the New Orleans levees. Waters levels in portions of Plaquemines Parish are only 3-5 feet lower than Hurricane Katrina 13-14 vs 17-19.

I cannot emphasize enough how poorly the Saffir Simpson scale it at relating storm impacts and the fact that this was only a Category 1 hurricane appears to have resulted in residents not heeding the evacuation orders. The focus during landfalling tropical cyclones must be on the impacts and NOT the category of the storm….the category only suggest wind damage impacts and has no relation on the storm surge or rainfall flood threat. Every hurricane is different, a slow moving large weak hurricane like Isaac can produce significant impacts as shown due to the far reaching effects and the continuous adverse conditions. Below are listed the storm surge values expected for the various portions of the affected coast as issued in an e-mail on Monday at 140pm. As you can see the values for Plaquemines Parish are highlighted in red (7-11ft), with the levees only 8ft tall it was highly likely that they would be overtopped.

SE LA (from the mouth of the MS River west to near Houma): 6-9 ft
SE LA (from the mouth of the MS River to the LA/MS state line): 7-11 ft
SE LA (Lake Pontchartrain): 5-8 ft
MS coast: 8-12 ft
AL coast: 6-10 ft
FL panhandle: 3-6 ft

Storm surge values along the coast will subside today as onshore winds weaken however areas where levees have been overtopped will take days to drain.

Isaac will continue to move inland and weaken however large feeder bands on the east side of the system will continue to produce flooding rainfall over MS and E LA. As the center moves NNW tonight into southern AR, the potential for core rainfall will increase. The threat will be shifting to fresh water flooding as Isaac moves north into AR , MO, and IL over the next 48 hours. While much of this region is suffering in severe drought, the very heavy rainfall of a tropical system in a short period of time can lead to flooding. Additional rainfall amounts of 6-15 inches will be possible along the track of Isaac.

[rtd2]

^^ Es no problema!

Will be interesting to see the official numbers on Isaac. Jackson county EOC (just east of me) is reporting 30 " of rain from Isaac. And its still raining there.

Those bands are just setting up and training over the same locations, over and over again. I've been watching the band over Jackson County and it has literally taken 8 hours to edge into western Mobile County on the Alabama side. I'm in West Mobile and, while there is rain, it's not the deluge going on 20 miles to the west along the state line.

STILL POURING in most of Jackson county...they been in that feeder band nearly 12 hrs

http://radar.weather.gov/ridge/radar.ph ... b&loop=yes

[artist]

Thanks HQ, Power is on finally ! Work tomorrow, and curfew is lifted!!

yay!!

[midnight8]

The dam on Lake Tangipahoa at Percy Quinn State Park in McComb, Ms has been overtopped and is failing. Complete failure is certain. Authorities are telling people in Kentwood and Robert, La to get out now. They have 90 mins before the water reaches them. Please call anyone you know in the area to let them know if they may not be keeping up with the news. This is a very dangerous situation.

Dang!!! My grandad is in McComb for a reunion. I just called him and he says he is not close enough for that dam to affect him. I hope he is right.

The lake is S/W of town and the dam is at the south end of the lake. Town should be well clear.

I know he is not actually in town. He is on a farm outside of town staying with some relatives. Hopefully they know the area well enough to know if they are safe. He seems to think they are ok.

[tolakram]

Rain bands still streaming in



Total precip estimates since this morning.



Regional Radar

[tolakram]

Mobile radar estimates.

[Extratropical1]

I'm still following Isaac both on the board and TWC day and night and I am in SW FL with no contacts on the northern gulf shores. My heart is breaking for all the devastation and lives destroyed once again.

Me too! I just don't post alot but learn alot! Thanks for all of the education and information you all provide on this board.

[tomboudreau]

Watching and waiting to see if Isaac is going to washout Labor Day and Tuesday, here in Pittsburgh.

[WeatherGuesser]

I think it'll still be in Ohio by then.

[midnight8]

Finally getting some rain in Orange just to the west of the Texas/LA state line. First drops I have seen.

[Janie2006]

What a difference a few miles can make, eh? West Mobile got anywhere from 6 to 8 inches of rain, while that Doppler estimate for Pascagoula and eastern Jackson County indicates around 20 inches of rain. And, yep, it's *still* raining over there!

[galaxy401]

Wondering how much rain Isaacs is going to give where I live. We are very dry but I don't want to stay inside the whole Labor Day weekend.