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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Quoting reef58:
There were some fairly high reports, but the common denominator is they were well above the standard height of 10 meters.

If you get real Cat 1 winds that is a strong storm. I think that should be emphasized.



That's a good point. A lot of people get caught up on categories, but they don't get the maximum sustained winds we advertise. The overwhelming majority people who experience a 115 mph hurricane, for example, don't see sustained winds even close to that.

So they extrapolate their experience for future hurricanes. Well, the weather man said I was getting 115 mph winds but the eye came real close and we never got anything over 50. So if the weatherman tells us we're getting an 80 mph storm, well heck, we'll be lucky if we get tropical storm force gusts. Then they actually get winds close to the maximum because the wind field is structured differently, and they're shocked.

And while CybrTeddy's right about the antiquated SSHS, coming up with a replacement is going to be hard to sell. Basically, you'd have to come up with a number for all of the forecast points to accurately describe the potential impact. And it's a lot easier for people to digest "Category 3 hurricane on the SSHS" than "it'll be a 5 out of 10 in Mobile, an 8 out of 10 around the Big Bend of Florida because of heightened storm surge, a 6 out of 10 in this other town because they'll be in the eyewall and have the highest winds but the coast outline makes it harder to build a large surge, etc..."

The people throwing a temper tantrum because the NHC refused to indulge their fetish for intensifying hurricanes is laughable and sad at the same time. Like an Owen Wilson movie. Except for the part about laughing. As has been posted repeatedly, the NHC is stacked to the gills with talented meteorologists using the best equipment and with more collective experience than we can imagine. Their job is to create a responsible forecast, not the worst-case or most media-friendly. Hurricane forecasting is an inaccurate science even in the best of conditions, but I don't care what odds you lay, when it comes to the NHC and a gaggle of anonymous commenters on a blog, the smart money moves heavy to Coral Gables.
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Quoting southfla:


My question was hypothetical and not related to any damage. Some of my neighbors' lack of preparations for Isaac, led me to think about the obligations that homeowner's might have related to their wind mitigation discounts.

That is a very fine line to walk. On one side, homeowners should only get wind mitigation discounts for being fully prepared. On the other hand, what about when the things you use for wind mitigation are more expensive than the discount? Hurricane shutters aren't cheap. Other things can be done that aren't quite as effective, but significantly cheaper.

(for example, I have impact-resistant double-paned windows, with smallish panes, and I also have Chinese Elm trees - which are highly hurricane resistant - covering one of the primary wind avenues approaching my house)
Member Since: August 3, 2008 Posts: 16 Comments: 5890
School here is cancelled for tomorrow, Vernon Parish.
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Quoting Carnoustie:


small world,first time back in 17 years,going back to the USA about Christmas,if immigration agree.:)


I'm from helensburgh, live in edinburgh!
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Plaquemines issued new evac orders for the Jesuit Bend area. Continued rain and surge coming upriver may cause more overtopping of levees.

"A mandatory evacuation has been ordered from the Oakville Flood Gate on Hwy 23 to Venice. Residents are urged to evacuate this area. A shelter will open at the YMCA in Belle Chasse located at 8101 Hwy 23. The shelter will open at noon today." Link

Poignant morning rescue story from the east bank in Plaquemines.

Member Since: October 9, 2005 Posts: 13 Comments: 495
Quoting dmh1026:
One of the major problems with a storm like Isaac is the amount of water on the ground. When the ground gets soggy from a slow moving hurricane, trees can be toppled by winds much easier than a faster moving higher wind speed hurricane. big problems in LA that are going to get worse each hour until it moves out.


Not to mention southern LA has had plenty of rain this summer.
Member Since: August 16, 2007 Posts: 0 Comments: 614
Quoting syn627:
I-10 near LaPlace, LA closed


Is that where the 10 bridge comes down at laplace headed northbound/westbound?
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Quoting syn627:
I-10 near LaPlace, LA closed

wow, not everyday an Interstate gets under water. If i read the mile post correctly in that pic (209) here's Google Maps showing what it normally looks like:Link http://goo.gl/maps/KA4Vz
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Good Afternoon Everyone!


The impacts of a weakening versus a strengthening storm is signficant. Isaac finally got vertically stacked, and the anti-cyclone moved overtop him making for a very favorable outflow regime.

This allowed the storm to continue to intensify despite land interaction, and brought legitimate category 1 sustained winds over a fairly good swath of far southeast LA.

Obvious the duration of the event is signficant is the damage it causes as well. We all have to be glad that there was just enough of an easterly shear from the anti-cyclone taking off to the north as the storm left Florida, otherwise we would probably have had a category 3 storm sitting in the same spot as Isaac is now moving just as slow...

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Local TV...WLOX...reporting that three people were arrested in Biloxi for looting. Sad, so very SAD!
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Quoting srqthymesage:


Thanks, Largo, had you in my sights to be protected. How's your peninsula faring re flooding? Stay safe, okay?

new gal from SRQ
..hi my county is fine, heavy flooding is in on the east coast, especially down in palm beach area,i think the whole gulf coast needs a week or two breather huh might not get it though but we will see..take care
Member Since: August 6, 2011 Posts: 4 Comments: 40965
Last few satellite frames actually show a ragged eye feature surrounded by ring of convection. Isaac is going down swinging.
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Heavy Rain Fog and Windy

77°F

25°C

Humidity96%
Wind SpeedSE 40 G 64 mph
Barometer29.53 in (1000.0 mb)
Dewpoint76°F (24°C)
Visibility0.25 mi
Heat Index78°F (26°C)

Last Update on 29 Aug 12:53 pm CDT

Current conditions at

Gulfport-Biloxi Regional Airport (KGPT)

Lat: 30.4 Lon: -89.07 Elev: 30ft.

More Local Wx | 3 Day History | Mobile Weather




Gosh, this reminds you just how scary huge Isaac is.

They've been getting hours of winds this strong way over in Mississippi.
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333. yoboi
Quoting Joanie38:
Hi everyone!! Alexandria,LA here...we still haven't experience Isaac YET...BUT SHOULD be starting late tonight...man, this is one SLOW storm!!!!


do ya think ya will get soaked later???
Member Since: August 25, 2010 Posts: 7 Comments: 2399
Quoting xtremeweathertracker:
NEW VIDEO BLOG UPDATE!!


"Error!

There was a problem opening this user's Wunder Blog files. Please try again later or check the requested URL."
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(click to enlarge)
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Quoting MNhockeymama:
Do any of you know the current number of power outages being reported for the GOM? I'm trying to find it, but the websites are overloaded and running very slowly. TYIA
Last I heard it was 615,000.
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Quoting RussianWinter:
BTW is 98L pretty much guaranteed to be a fish storm?

Much too soon to be making any guarantees.
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Quoting AuntyCyclone:


It's possible that the damage resulting from lack of hurricane shutter installation might be paid (or not). Is the amount of damage over your deductible to begin with?

Without reading your policy and the paperwork associated with the mitigation that resulted in your premium discount, I would only be guessing.


My question was hypothetical and not related to any damage. Some of my neighbors' lack of preparations for Isaac, led me to think about the obligations that homeowner's might have related to their wind mitigation discounts.
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Quoting Masquer08er:
Since Isaac's slight move N, the northern part of Mobile County and now Clarke County is catching some significant rain. This morning only the lower half was getting anything worth noting. I was hoping we were done with it. School starts back tomorrow,


My thoughts exactly. Getting pounded with rain now!!
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98l
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Quoting weathermanwannabe:
and Isaac is going to be able to stay near Category 1 hurricane strength all day today.

Incredible really; assuming that he has started to weaken a little bit (and unwind his circulation), the broad circulation to the East is now causing training bands far away from the COC over parts of the West Coast of Florida and the Big Bend.

Never seen anything like this from a "landfalling" storm hundreds of miles away.


Getting LOTS of rain and wind gusts in Mobile, Al.
Worse than yesterday. It's shocking, really, that he is still a hurricane.
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BTW is 98L pretty much guaranteed to be a fish storm?
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Hello,

Been a long time since I posted on the blog. Things are good here in Ponchatoula so far. We still have power for now and only getting gusts to maybe 50mph. Seems the wind field is much worse to our south and west. Stay safe everyone!!!!
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Since Isaac's slight move N, the northern part of Mobile County and now Clarke County is catching some significant rain. This morning only the lower half was getting anything worth noting. I was hoping we were done with it. School starts back tomorrow,
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Quoting floridaT:
and how do those folks in places like Idaho feel about never getting any of the money?


Idaho declares disaster status with FEMA on average once per year:

Link to FEMA stats for Idaho

Just this year MONTH they received funding to help fight the Trinity Ridge Fire. Here's a link to the story.
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Quoting Joanie38:
Hi everyone!! Alexandria,LA here...we still haven't experience Isaac YET...BUT SHOULD be starting late tonight...man, this is one SLOW storm!!!!


Joanie, those winds outside are part of Isaac. Be careful as he moves in tonight.
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Quoting oddspeed:
LoL, these so-called conservatives are always the first to whine for help when times get tough.
One would think Jindal would have come around after all the disasters he's presided over but i guess that is expecting too much.


Disaster assistance is one of the fundamental functions of the Federal Government and it's the Governor's responsibility to follow the established processes. It's for the people in his state.

I don't get what politics has to do with it...

FEMA’s Disaster Declaration Process: A Primer
http://www.fas.org/sgp/crs/homesec/RL34146.pdf
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I-10 near LaPlace, LA closed
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Quoting LargoFl:
Braithwaite rooftop rescue


Thanks, Largo, had you in my sights to be protected. How's your peninsula faring re flooding? Stay safe, okay?

new gal from SRQ
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Quoting SWLACajun:


He is. Sorry thing is our tax dollars go to feds for homeland security and FEMA and then we have to go beg to have them give 'em back to us when we have an emergency need for them. Begging for our own stuff back....go figure. No more politics for me now.


Oh please....Louisiana has received far over their far share of Federal assistance and funding during the past decade.....
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Quoting alaina1085:
GFS handeled this storm well I think... better then the other models.. But boy they had a hard time pin pointed Isaac thats for sure.


Yeah Isaac was one of the weirdest tropical cyclones every in my opinion. I think part of the reason Isaac was so hard to forecast in terms of intensity and track is the strange behavior of it's inner core. Also steering currents were also quite complex for a while.
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Hi everyone!! Alexandria,LA here...we still haven't experience Isaac YET...BUT SHOULD be starting late tonight...man, this is one SLOW storm!!!!
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Quoting reef58:
You make a good point but the HH have access to equipment to show them where to sample for the highest winds. They may not get the exact highest, but they are getting pretty close.



Agreed that their data is probably very good data. Just figure that in the end, we'll never know whether the winds people say they experienced were accurate estimates -- they could well be. We don't have the data, that doesn't mean local conditions didn't mix some very nasty winds down for a bit.

I think their equipment gives them solid data, but it's always got to be taken into account that data is not the whole picture of anything. As a scientist, it's just as important to understand what your data _isn't_ telling you, as it is to see what it _is_.

And I'll leave the subject alone otherwise for now, it doesn't need to eat the thread. There's plenty of time later when people are out of harm's way.

Just tired of some of the back and forth on this stuff that misses the point. You don't have to disbelieve people's first person accounts _or_ think the data is wrong, folks. Multiple things can be true at the same time, and we'll never really know beyond the data that we have -- that's all we can go on for sure -- but people who have lived through lots of this stuff are not people I'm going to just discount when they say what they personally experienced.
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Quoting RitaEvac:
We can see the cloud shield well outside looking east here in the Houston/Galveston area. Wind advisory in effect till 8PM and winds are brisk when out to lunch, reminiscent of a cold front but with heat and drier air



We're starting to see the winds pick up out of the NNE here north of Austin as well. Definitely keeping an eye on elevated fire conditions today and tomorrow. Thoughts and prayers are with our neighbors in Louisiana right now and will be ready to assist wherever possible.
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Quoting fragileuk:


Can't believe this I'm in Wemyss bay!


small world,first time back in 17 years,going back to the USA about Christmas,if immigration agree.:)
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Quoting luvtogolf:


I have a question. When the HH's report winds of let say 80mph and the NHC classifies the winds as such. Is that one measurement at one spot or do they need more than that? Just curious.


It is based on only one region, because when they set an intensity it technically is "max sustained winds". Obviously winds will vary even in the core of the storm that's just the nature of wind physics and physics itself. 80 mph winds won't ever mean a uniform and even 80 mph ring of winds around the eye. Winds may be 55 mph for a bit and all the sudden increase to over 70 mph with gusts to 90 mph, for example during passage in the eye.
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NEW VIDEO BLOG UPDATE!!
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Quoting SFLWeatherman:
98L is now up to 80%


I don't see that ...

Shower and thunderstorm activity continues in association with a broad area of low pressure along a tropical wave located about 900 miles west of the Cape Verde Islands. While development is not imminent...environmental conditions appear conducive for a tropical depression to form in the next day or two. This system has a high chance...60 percent...of becoming a tropical cyclone during the next 48 hours as it moves westward to west-northwestward at 15 to 20 mph.
Read more at http://www.wunderground.com/tropical/ABNT20.html#u sxcWJqV3zOuC8IP.99
Member Since: April 23, 2011 Posts: 104 Comments: 14873
Just regarding Kirk's formation status,

According to the wikipedia formation list, it tied three other storms for second earliest #11 storm formation:

Katrina August 24, 2005
Unnamed August 28, 1933
Unnamed August 28, 1936
Karen August 28, 1995
Kirk August 28, 2012
Link

But Dr. Masters has said:
"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."

I'm just pointing out that the two are different...
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98L is now up to 80%
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Quoting ringeaux:


Each storm is going to be worse than the previous and we lose barrier islands and marsh that used to buffer and knock down surge. Places that didn't flood with this storm will with the next and so on.


While those are contributing factors, the major issue is that levees and flood walls were reinforced further north in New Orleans. While they may be working to protect the NOLA metro area now, they allow water to increase in both flow rate and amount downstream. Those levees and flood walls will continue to be raised, and people downstream will continue to see worse flooding. The only options are to abandon areas downstream and allow them to flood, or start abandoning areas around NOLA so they can be uses as overflow retention basins. The present system of flood protection in NOLA will not hold without a constant increase in height, and even they will eventually fail in a larger storm. There is only so much air you can put in a balloon before it bursts.
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Quoting LurkyMcLurkerson:
I'll add to my post above that, as somebody who has dealt with plenty of actual data collection (in very different scientific fields from this), data is the best representation of truth you can get -- but it's not going to capture everything that happens, it is not the _only_ truth. It's data, it's the factual stuff that you can rely on (for the most part), but there's very often plenty of factual stuff that data can never capture.

Something being experienced but not backed up by measurement doesn't make it not true. It makes it unsupported by the collected data. There's a huge difference.

I hope folks are faring as well as possible with whatever conditions they are _still_ experiencing.



Don't forget that the wind field is a gradient, so the area with maximum winds could be fairly small and not very well represented on data sensors such as buoys. Furthermore wind measurements at the local level can be inhibited or enhanced by things like say trees or buildings or topography.
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Quoting RussianWinter:


A fast moving, small, category 1 storm that is on the weaker end that has a small hurricane force wind field doesn't do much damage to areas that are well prepared for it.

Isaac isn't no weakling, he has storm surge, he stayed over an area for a long amount of time.

The comparison between an ordinary category one hurricane and Isaac is closer to the comparison between 2010 tropical storm Bonnie and 2001 tropical storm Allison.
One of the major problems with a storm like Isaac is the amount of water on the ground. When the ground gets soggy from a slow moving hurricane, trees can be toppled by winds much easier than a faster moving higher wind speed hurricane. big problems in LA that are going to get worse each hour until it moves out.
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ATCF says Isaac is a tropical storm once more...

AL, 09, 2012082918, , BEST, 0, 298N, 908W, 60, 974, TS, 50, NEQ, 50, 50, 25, 25, 1007, 275, 45, 0, 0, L, 0, , 0, 0, ISAAC, D
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I don't have access to TV at work but would love a report on what the folks are saying on TWC as to the current structure. Just looking at the radar loops, it looks like the eye is starting to weaken and collapse a bit. On the flip side, it keeps hugging the coast and building more moisture on the West flank which was drying out earlier today.......Just keeps feeding off the Gulf.
Member Since: August 8, 2006 Posts: 0 Comments: 9329
Quoting floridaT:
i thought Jindal was for "smaller gov"


Sometimes you need government, you know, to help people out in times of disaster.

The term "small" government is just a catchy term for people to spread around for popularity. However, when they mean "small" government, they are talking about less centralization of government and less state control of economics.

But one of the main roles of the government is to come to aid during disaster, if money is spent in doing so, even large amounts. It is necessary in order to save lives and I sure hope that's something everyone can agree on regardless of political views. This isn't about republican or democrat in times of trial, it's about saving lives which should remove political debate and boundaries and bring people together to do what it takes to save people even if those people ignored evacuations and don't want to save themselves. I hope we all love human life more than money, I mean not to turn this into a political debate, I'm just expressing something I believe is important.
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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.