Isaac pounding Louisiana, Mississippi, Alabama, and Florida

By: Dr. Jeff Masters , 4:01 PM GMT on August 29, 2012

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Hurricane Isaac continues to lumber slowly northwestwards at 6 mph, as it pounds Louisiana, Mississippi, Alabama, and Florida's Panhandle with torrential rains, high winds, and a damaging storm surge. The eye was partially over water for most of the 15 hours after Isaac's official landfall at 7:45 pm EDT Tuesday night, but New Orleans radar shows the eye of the storm is now fully ashore near Houma. The radar echoes show some weakening on the west side of the eyewall, where dry air has infiltrated the storm. Wind shear remains light, and upper level outflow over Isaac is as impressive as we've seen so far, with a strong outflow channel to the north, and a respectable one to the south, as well. Infrared and visible satellite loops show a very large, symmetric, and well organized storm, and Isaac is going to be able to stay near Category 1 hurricane strength all day today. This will allow Isaac to drop rainfall amounts of 15 - 20" in some areas of Louisiana before the storm is over. A few rainfall totals from Isaac through 11 am EDT:

9.26" New Orleans Lakefront Airport
5.59" Belle Chasse, LA
5.21" Mobile, AL
3.65" Hattiesburg, MS
3.42" Gulfport, MS
2.81" Biloxi, MS


Figure 1. Morning radar reflectivity image from New Orleans.

A dangerous storm surge event underway
Isaac is bringing a large and dangerous storm surge to the coast from Central Louisiana to the Panhandle of Florida. Late this morning was high tide along much of the coast, and the highest water levels of Isaac are likely being experienced at many locations. At 11:30 am EDT, here were some of the storm surge values being recorded at NOAA tide gauges:

8.0' Waveland, MS
8.2' Shell Beach, LA
2.0' Pensacola, FL
4.6' Pascagoula, MS
3.4' Mobile, AL

The peak 11.06' storm surge at 1:30 am EDT this morning at Shell Beach, which is in Lake Borgne, 20 miles southeast of New Orleans, exceeded the 9.5' surge recorded there during Category 2 Hurricane Gustav of 2008. In general, the storm surge heights from Isaac have been more characteristic of a strong Category 2 hurricane, rather than the weak Category 1 hurricane one might suppose Isaac is, based on its top sustained winds of 75 - 80 mph. The Saffir-Simpson Scale for ranking hurricanes is only a crude measure of their potential impacts.

A storm surge estimated at 12' moved up the Mississippi in Plaquemines Parish near Port Sulphur, LA, near 8:30 pm EDT Tuesday, causing overtopping of the levees and flooding of homes in the mandatory evacuation areas behind the levees. These levees were not part of the $14.5 billion levee upgrade New Orleans got after Hurricane Katrina, and were not rated to Category 3 hurricane strength, like the levees protecting New Orleans are. The surge continued upriver, elevating the water levels 10' in New Orleans (103 miles upstream from the mouth of the Mississippi), 8' in Baton Rouge (228 miles upstream), and 1.4' at Knox Landing, an amazing 314 miles upstream. The river was 7' low due to the great 2012 U.S. drought, and I suspect the near-record low flow rate of the river allowed the storm surge to propagate so far upstream. The salt water from the storm surge will be slow to leave the river, due to the continued winds of Isaac keeping the surge going, plus the very low flow rates of the river. One benefit of the heavy rains of 10 - 20 inches expected to fall over Louisiana over the next two days will be to increase the flow rate of the Mississippi River, helping flush the salt water out of the river. The low flow rates of the Mississippi had allowed salt water to move upriver to just south of New Orleans over the past few weeks, threatening the drinking water supply of Plaquemines Parish.


Figure 2. Tide gauge data from Waveland, Mississippi. The green line shows the storm surge. The red line is the storm tide, the height of the water above Mean Sea Level (MSL.) The storm tide at Waveland currently (9') is 2' higher than that of Category 2 Hurricane Gustav of 2008. Image credit: NOAA Tides and Currents.

Tropical Storm Kirk in the Central Atlantic
Tropical Storm Kirk formed Tuesday night in the Central Atlantic. Kirk's formation at 03 UTC on August 29 puts 2012 in 4th place for earliest formation date of the season's 11th storm. Only 2005, 1995, and 1933 had an earlier formation date of the season's 11th storm. Kirk should stay well out to sea and not trouble any land areas.


Figure 3. Morning satellite image of Tropical Storm Kirk.

Invest 98L in the Eastern Atlantic
A tropical wave (Invest 98L) is about 750 miles west-southwest of the Cape Verde Islands, and is moving west to west-northwest at about 15 mph. In their 8 am EDT Tropical Weather Outlook, NHC gave 98L a 50% chance of developing by Friday morning. Several of the models develop 98L into a tropical depression by this weekend, but none of the reliable models foresee that 98L will be a threat to the Lesser Antilles. The storm may be a threat to Bermuda next week, but it is too early to say if it may threaten the U.S.

Jeff Masters

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It may or may not be retroactively bumped up to Cat 2 depending on data later, but ultimately I think the point is that hurricane force winds of any kind, and tons of rain and surge to go with them, can cause huge damage. Especially if they're sustained over a long period of time.

Structures and trees and powerlines can go down in one huge gust, or they can slowly be eaten by hours and hours of lower (but still nasty) wind until they give. And ultimately, the surge and rainfall is every bit as important as the wind, in figuring out the danger.

I think personally that the NHC should rethink how they communicate about these storms -- I think people rely on the scale, but the scale can only tell you about predicted wind speeds, never about the many other factors that can make even a strong tropical storm into a very dangerous situation. They try to add that info, but all that gets through to a lot of people is the category, the rest only filters to those who are attentive.
Member Since: August 26, 2012 Posts: 0 Comments: 368
I did see some reports with winds sustained at around 75kts over buoys, the 110mph gusts would certainly tend to cause one to believe it was stronger than the recon was showing on the SFMR last night. The flight level winds certainly indicated a stronger system, howver from all indications they weren't mixing down to the surface.
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Quoting hurricanehanna:


supposed to pass between Lafayette & Baton Rouge....won't be missing us.

I can ask where my mother heard it and let ya'll know
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by NHC definition, it was a cat-1.

We do know:
-pressure was notably low for a TS/cat-1
-storm motion was slow
-it nearly stalled just off the coast, and has moved little since landfall

You cant just say "this was a Cat-2". The surge was high, but surge is no longer part of the formula. Frankly it took everything they had to make it a cat-1.

There's a NHC definition, as in definite. You are welcome to devise (and please explain) the logic for how you define storms.
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Quoting Tazmanian:
now you guys now what the power of a cat 1 hurricane can do


It seems that the surge and extreme rainfall are the real damage culprits in a minimal hurricane (cat. 1) affecting this area. According to Wunderground, the highest winds in New Orleans were 45 gusting to 70 mph, yet the water damage will be substantial in many areas. I just really am hoping nobody has to lose their lives to Isaac.
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Two live chase feeds,LIVE news feed and chat room for Hurricane Isaac

Stormjunkie starting to get surge near Biloxi,MS.
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190. IMA
Quoting Photonetic:
I don't think it's fair to call anyone heartless for having a larger perspective on the situation. These people committed a selfish act after they were told that their homes will be inundated, their lives will be in danger and that rescue would be difficult. Through their shortsightedness they are draining the resources of emergency personnel away from those in danger through no fault of their own and making an already enormous task that much more difficult. You or I or any of the posters here would have the heart to reach out to such people in our own lives if faced with a similar situation and try to dissuade them from choosing their willful self-interest over their neighbor's desire to keep them from harm's way. My heart goes out to those rescuers who are forced to save these people who passed up the chance to save themselves.
Very, very well-put.
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Quoting reedzone:


In the end, and we all know, this wasn't a Category 1 storm. Local station reported many gusts over 100 mph, some 120 mph. I believe this made landfall as a Category 2 Hurricane with 100 mph. winds. Pressure of 968 mlb. (equals to an upper end 2/low end 3 storm). Isaac will most likely be retired.


You are delusional.
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Of the other
systems out there...none are predicted for the gulf any time soon...right??
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Quoting GeauxGirl:


Where did you hear this?
Quoting JasonRE:
Ok, now I hear that the storm may miss us by going North and towards Jackson, MS.

Who do I listen to? Gov. Jindal said that the NHC said that it's still moving WNW.


supposed to pass between Lafayette & Baton Rouge....won't be missing us.
Member Since: September 5, 2007 Posts: 0 Comments: 3481
The people affected likely don't care about the cat. They care about the effects. I don't see how inaccurately saying this is a cat2 storm will help them in a meaningful manner, or even make them feel better.

Quoting reedzone:


Tell that to those affected.. This was most likely a low end Category 2 storm.
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New Orleans Live stream..ongoing news and updates.

Link
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Quoting JasonRE:
Ok, now I hear that the storm may miss us by going North and towards Jackson, MS.


Where did you hear this?
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Quoting SteveRose:
Isaac dumped over 16" of rain on Wellington, FL - 12 miles inland from West Palm Beach, FL Sunday - Tuesday. Flooding there continues to make many roads impassable for 3-4 days now as the storm sewers are not allowing water to drain - because where they are draining/pumping into - canals - are also heavily flooded. This breaks the recent rain record for Wellington from a single hurricane set by Irene 12 years ago. May be the most rain from a single tropical storm there in 50 - 100 years.

Today's Palm Beach Post reported that Wellington, FL recv'd 18" in the past 72 hours. In my neighborhood (about 6 miles SE of Wellington) it wasn't quite that bad. Maybe 13" of rain... second worst since T.S Irene 12 years ago.


Picture of Loxahatchee Groves - west area of P.B. County.

Gov. Rick Scott addresses press in Palm Beach Co.
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Quoting reedzone:


In the end, and we all know, this wasn't a Category 1 storm. Local station reported many gusts over 100 mph, some 120 mph. I believe this made landfall as a Category 2 Hurricane with 100 mph. winds. Pressure of 968 mlb. (equals to an upper end 2/low end 3 storm). Isaac will most likely be retired.
I understand you by nature question the NHC, but don't include me in that "all of us". The NHC had thousands of reports at their disposal, at all levels of the atmosphere. This wasn't a storm 1000 miles out to sea here. It's a Cat1, and it's not gonna' change in the off-season.
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Quoting Dsntslp:
Largo,

Thank you for all you do, truly.

This blog and your posts is how I stayed updated when we were getting so much rain and flooding in FL.

Like many others in todays economy we have no cable but we do have computers hooked to all of the televisions. The drawback to this is that most of the online broadcasts are so choppy in loading and buffering that it is almost impossible to make out what is being said at times. We even had trouble with our smart phones.

I suppose I need to get a weather radio but I have seen so many postings over the years where people online say that they did not receive a local transmission that others online had just heard.

I wonder if it might help if WU had two threads for major events such as this. One thread for posting emergency info and one for chat?? Just an idea, but then I see that there are chat rooms listed above this box I am typing in as "Weather Chat" and " Tropics Talk". Are those rooms open to all posters here and is it alright to use them to just chat, catch up with friends etc...

I think that people who use their smart phones for internet and come here for updates would have a much easier time if there was a dedicated info area with minimal chat.

Anyway, I truly thank you for your efforts to keep us informed. Truly.

(Sorry so long winded here y'all.)





Try this link. It has good coverage and no delays over here. Link
Member Since: July 30, 2011 Posts: 2 Comments: 619

Quoting JasonRE:
Ok, now I hear that the storm may miss us by going North and towards Jackson, MS.

Who do I listen to? Gov. Jindal said that the NHC said that it's still moving WNW.
NHC will be releasing an intermediate advisory at 2pm eastern daylight time... another 30 minutes and you will have the latest information.
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Perhaps you should start your own exclusively Louisiana blog. This one is concerned with tropical weather. Nobody is "tired" of hearing about Isaac, but the world does not stand still because you want it to.

Quoting LAlurker:
Really, fellow bloggers, I know that many of you are tired of Isaac after 2 weeks of postings, but this is still going on here in LA, a lot still happening, still classed as a Cat 1 by NHC. Can you please refrain from posting about invests and TDs that won't affect anyone for days, weeks, or never. Give Isaac another day or two. Thanks!
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Quoting reef58:
There have been no Cat2 winds reported. I think what you have seen is a hurricane which was accurately measured. I have seen many in the past which were over reported with the NHC reasoning that all winds were not sampled, or flight winds were x so we assume surface winds are y, ect.

Maybe McNabb is for accurate reports, and I suspect people will gain a better appreciation for cat 1 storms.



Tell that to those affected.. This was most likely a low end Category 2 storm.

the Mayor is actually challenging the NHC to go back and research Isaac more because he thinks it was a Major Hurricane, course it wasn't but a Category 2 is deff in the books.
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There have been no Cat2 winds reported. I think what you have seen is a hurricane which was accurately measured. I have seen many in the past which were over reported with the NHC reasoning that all winds were not sampled, or flight winds were x so we assume surface winds are y, ect.

Maybe McNabb is for accurate reports, and I suspect people will gain a better appreciation for cat 1 storms.

Quoting reedzone:


In the end, and we all know, this wasn't a Category 1 storm. Local station reported many gusts over 100 mph, some 120 mph. I believe this made landfall as a Category 2 Hurricane with 100 mph. winds. Pressure of 968 mlb. (equals to an upper end 2/low end 3 storm). Isaac will most likely be retired.
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Quoting Tazmanian:
now you guys now what the power of a cat 1 hurricane can do


jugtst imagern iof it was a CAT4 liek you were predicting last night?
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Quoting hamla:
cnn just said that hwy 90 in ms washed away anyone have info??/


Wouldn't be the first time!
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We are getting pounded in Baton Rouge and to think the eye won't be here until tonight.
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Quoting JasonRE:
Ok, now I hear that the storm may miss us by going North and towards Jackson, MS.

Who do I listen to? Gov. Jindal said that the NHC said that it's still moving WNW.


NHC and your local NWS..please heed THEIR warnings..
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Quoting TreasureCoastFl:
No! OMG! Thats awful!

Those look like nice homes too...

What a shame. Hope everyone is safe.
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Quoting ncstorm:


I posted this earlier this morning but Good Morning America showed in NO where they were having hurricane parties at bars until 12am today..some people just didnt take the threat seriously..


I doubt the party was so lively outside of the levees..

It's a lot easier to party behind 14.5 billion dollars levees than it is outside of them
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Quoting A4Guy:


How did you get that pic of Biloxi by the Beau Rivage casino? I was just there last week - would like to see if there are other webcams or bloggers there posting images.
Thanks!
Go to Coast Life on Facebook if you can. They have posted a bunch. I think they also have a website.
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Quoting Tazmanian:
now you guys now what the power of a cat 1 hurricane can do


In the end, and we all know, this wasn't a Category 1 storm. Local station reported many gusts over 100 mph, some 120 mph. I believe this made landfall as a Category 2 Hurricane with 100 mph. winds. Pressure of 968 mlb. (equals to an upper end 2/low end 3 storm). Isaac will most likely be retired.
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Ok, now I hear that the storm may miss us by going North and towards Jackson, MS.

Who do I listen to? Gov. Jindal said that the NHC said that it's still moving WNW.
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166. hamla
cnn just said that hwy 90 in ms washed away anyone have info??/
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Quoting USCGLT:
Evac orders came pretty late on Isaac due to the constant movement of the cone. I know it seems simple to most to evacuate when told to do so...having evacuated numerous times I can assure you it is not. Finding a place to stay is often problematic, and not everyone has the resources to leave even though they may want to. Of course there are also the "die hards" who have the ability to leave and don't, those are the ones I dont have sympathy for...


I posted this earlier this morning but Good Morning America showed in NO where they were having hurricane parties at bars until 12am today..some people just didnt take the threat seriously..
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Quoting GTcooliebai:
This is in Braithwaite, LA (Plaquemines Parish).

No! OMG! Thats awful!
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Largo,

Thank you for all you do, truly.

This blog and your posts is how I stayed updated when we were getting so much rain and flooding in FL.

Like many others in todays economy we have no cable but we do have computers hooked to all of the televisions. The drawback to this is that most of the online broadcasts are so choppy in loading and buffering that it is almost impossible to make out what is being said at times. We even had trouble with our smart phones.

I suppose I need to get a weather radio but I have seen so many postings over the years where people online say that they did not receive a local transmission that others online had just heard.

I wonder if it might help if WU had two threads for major events such as this. One thread for posting emergency info and one for chat?? Just an idea, but then I see that there are chat rooms listed above this box I am typing in as "Weather Chat" and " Tropics Talk". Are those rooms open to all posters here and is it alright to use them to just chat, catch up with friends etc...

I think that people who use their smart phones for internet and come here for updates would have a much easier time if there was a dedicated info area with minimal chat.

Anyway, I truly thank you for your efforts to keep us informed. Truly.

(Sorry so long winded here y'all.)



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now you guys now what the power of a cat 1 hurricane can do
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Quoting catastropheadjuster:
I was just told the causeway in Mobile,Al is completely underwater,this isn't the bayway. On the news they said it looked like Mobile Bay was angry.

Sheri


Dang.
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This is in Braithwaite, LA (Plaquemines Parish).

Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting SteveRose:
Isaac dumped over 16" of rain on Wellington, FL - 12 miles inland from West Palm Beach, FL Sunday - Tuesday. Flooding there continues to make many roads impassable for 3-4 days now as the storm sewers are not allowing water to drain - because where they are draining/pumping into - canals - are also heavily flooded. This breaks the recent rain record for Wellington from a single hurricane set by Irene 12 years ago. May be the most rain from a single tropical storm there in 50 - 100 years.
Yup. We got 11" in St Lucie. Was a very strange and unexpected event with lots of flooding for us as well. I hope they are all fairing well on the gulf coast. Are any gulf posters posting?
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Test.
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Quoting dmh1026:
I hope everyone here takes note as those that ignored the authorities and chose to stay despite the warnings, are now showing all of us what can and does happen in these storms. Nobody can tell ahead exactly what will happen when a storm like this strikes. This is a very good education for all of us living in a hurricane zone!
I feel badly for all of them, and hope the loss of life is minimal. Stay strong LA!!!
Evac orders came pretty late on Isaac due to the constant movement of the cone. I know it seems simple to most to evacuate when told to do so...having evacuated numerous times I can assure you it is not. Finding a place to stay is often problematic, and not everyone has the resources to leave even though they may want to. Of course there are also the "die hards" who have the ability to leave and don't, those are the ones I dont have sympathy for...
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I was just told the causeway in Mobile,Al is completely underwater,this isn't the bayway. On the news they said it looked like Mobile Bay was angry.

Sheri
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Blasted server! Looks like we crashed the blog...
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by the time it is done some places in eastern LA may see isolated 24 inch rain totals
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A band from Isaac dropped nearly an inch of rain in an hour in Tallahassee earlier this morning. I can only imagine how people are fairing closer to the action with this pest of a system. Stay safe everyone!
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Looks like it is finally moving more North than West a very good sign.
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I personally think this thing will make a move to the West and we may end up on the path of the eye or even possibly on the east side here in Lafayette. What do the models show?
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Quoting AegirsGal:
Back when it was still moving across the Keys, didn't a few of the forecast models have Isaac just 'hanging out' for a day or so on the coast before moving on? It seemed inconceivable to almost everyone on the blog at the time.

Prayers to those covering the storm and to the emergency personnel tasked to deal with it.


Yes. We all thought it was too weird to be true.

It is so, so, so lucky that this thing didn't get stronger earlier than it did. Still no small thing by any stretch, but this could have easily been absolute, unthinkable catastrophe.

Ain't over yet. Good luck to all.
Member Since: August 26, 2012 Posts: 0 Comments: 368
148. Skyepony (Mod)
Near Slidell..

Member Since: August 10, 2005 Posts: 162 Comments: 37820
Quoting pottery:
Isaac running at 973 pressure at noon. Category 1.?????
This is one Freaky storm !

So sorry to see/hear of the hardship and losses.
Cant seem to find any sympathy for the ones that stayed put and are in trouble though. Tough !


Please..dig deeper.
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Nightime (just after midnight yesterday morning) image of moonlit Isaac approaching Lousiana, from NASA's Suomi-NPP weather satellite. Click for larger image and story:

NASA


Technology: plus 1,000. Awesomeness: plus 1,000,000.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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