ATL: ISAAC - Post-Tropical - Discussion

[gboudx]

Is New Orleans levy's going to be able to hold does anyone know???

Corps of Engineers says they will withstand up to Cat 5.

[tropicwatch]

Personal Forecast Disclaimer:
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.


I think it is possible that the approaching front has progressed further east and south than anticipated. This might be starting to influence Isaac a little bit.

[Dean4Storms]

Lets hope this northerly motion is just a jog!

http://climate.cod.edu/flanis/2km.php?l ... mimages=24

[capepoint]

85 knots sustained =
98 miles an hour
157kmhr

Gusting too 105 knots =
121 miles an hour
194kmhr

If these figures from NHC are true, Isaac will be a damaging storm wind wise upon landfall too.

Wind speeds given by NHC in forcasts are MAXIMUM SUSTAINED winds. It is unusual to actually see those numbers unless you are right on the beachfront with winds coming from offshore. Of course, there are usually vortices and tornadoes in a landfalling hurricane that will have locally higher windspeeds a little inland as well.
With that being said however, you could easily see some 80-85+ sustained with higher gusts in a storm labeled 100 mph.
But yes, if it reaches the forecast intensity, there will be a lot of wind damage as well.

Personal Forecast Disclaimer:
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

[Weather Watcher]

New Orleans levees can hold back a cat 3. Everything else will over top. They won't fail.

My company built a lot of the new ones, did repairs, and did some pump station stuff. We wanted to make it cat 5 "proof", but let's just say we had trouble convincing people of that.

Don't worry people. You are much better prepared this go round. Still not ideal though, expect some over toppings at some places.

Sent from my HTC One X using Tapatalk 2

Thank you for your answer.

Now I have a new question, this is quoted from Dr. Jeff Masters blog: "Isaac's southeast side continues to struggle with dry air and wind shear, which could help to moderate Isaac's intensity as it approaches the coast."

How can the dry air and the wind shear help it "moderate Isaac's intensity as it approaches the coast" ?

[N2Storms]

[quote="Dean4Storms"]Lets hope this northerly motion is just a jog!

http://climate.cod.edu/flanis/2km.php?l ... mimages=24[/quote]



Look at that big dry slot to the east of Isaac...almost no precip in that at all. Looks like we might not get much rain out of this after all and that's a good thing because the ground up in these parts just can't take much more rain.

[Zanthe]

New Orleans levees can hold back a cat 3. Everything else will over top. They won't fail.

My company built a lot of the new ones, did repairs, and did some pump station stuff. We wanted to make it cat 5 "proof", but let's just say we had trouble convincing people of that.

Don't worry people. You are much better prepared this go round. Still not ideal though, expect some over toppings at some places.

Sent from my HTC One X using Tapatalk 2

Thank you for your answer.

Now I have a new question, this is quoted from Dr. Jeff Masters blog: "Isaac's southeast side continues to struggle with dry air and wind shear, which could help to moderate Isaac's intensity as it approaches the coast."

How can the dry air and the wind shear help it "moderate Isaac's intensity as it approaches the coast" ?

I think you misunderstand what he was saying. It would make Isaac weaker, because that's what dry air and wind shear does.

[MGC]

I agree, it looks like Isaac is starting to deepen at a good rate...only negative is dry air to the east. Hopfully Isaac takes a big gulp of that dry air to put the brakes on intensification.

Was a beautiful day here on the Mississippi Coast. Earlier, as the cirrus started to pass overhead, I saw a beautiful double halo around the sun. Looked like a rainbow around the sun....beautiful. Sea birds except for a few have all flown the coop......MGC

The above is the opinion of MGC and not an official forecast.

[Weather Watcher]

New Orleans levees can hold back a cat 3. Everything else will over top. They won't fail.

My company built a lot of the new ones, did repairs, and did some pump station stuff. We wanted to make it cat 5 "proof", but let's just say we had trouble convincing people of that.

Don't worry people. You are much better prepared this go round. Still not ideal though, expect some over toppings at some places.

Sent from my HTC One X using Tapatalk 2

Thank you for your answer.

Now I have a new question, this is quoted from Dr. Jeff Masters blog: "Isaac's southeast side continues to struggle with dry air and wind shear, which could help to moderate Isaac's intensity as it approaches the coast."

How can the dry air and the wind shear help it "moderate Isaac's intensity as it approaches the coast" ?

I think you misunderstand what he was saying. It would make Isaac weaker, because that's what dry air and wind shear does.

Thats what I thought too

[WxGuy1]

JB has a point when he wonders how a 1007 mb storm can have 65 mph winds and a 981 mb storm can have 65 mph winds. 26 mb's is a huge difference.

I know! I know! It's because the winds yesterday were a bit (way) overstated by the advisories. The NHC doesn't like to lower a storm's wind speed as it's near land. This means sometimes saying a storm has 65 mph wind when the actual winds are closer to 50. They never want to give the public any reason not to heed TS warnings. Their goal is to protect lives and I can't fault them for that.

while such a goal is laudable the problem is that they're building complacency over time. Tampa bay just endured another TS warning with winds that were barely strong enough to keep the mosquitoes at bay. Just when you think complacency can't get worse, it gets reinforced. Frankly, if 50mph is a tropical storm (as compared to 65mph) there's no reason to overstate intensity. i am convinced that windfields are way overdone as are warnings and one day that could contribute to a real disaster.

It's worth noting that the SS category and wind estimates provided by the NHC are MAXIMUM winds. These are typically experienced over a VERY SMALL area of the storm. For a tropical storm that as 60 kt winds, the VAST majority of the area being affected by Isaac has winds much weaker than 60 kts. Again, these are the MAXIMUM winds, and they are very rarely sampled directly by surface observation sites. Heck, even for a Cat 4 storm with 140 mph winds, the change in the wind speeds with distance for the center tends to be very significant (varies from storm-to-storm, obiously). In addition, these strongest winds tend only to be experienced at the coast on the right side of the storm (the "onshore" side), and wind speeds tend to weaken significantly as one heads inland.

Tampa Bay was a very large distance from the center of Isaac, and I don't think anyone should have expected to see 50-60 kt sustained winds from Isaac in Tampa Bay yesterday.

Part of the issue is that the media report the SS category and MAXIMUM wind speeds usually without stating that these strongest winds usually affect a very small area. From all of the tropical cyclone landfalls I've followed that have affected the U.S., I've seen very few that have been accompanied by actual observations at surface weather stations that have matched the "maximum" wind potential.

I mention this not to undermine the wind speeds given. It is important to remember that you probably won't see those maximum winds, even if you live near the landfall location. If you're 50-80 miles from the landfall, especially on the offshore / left side of the cyclone, it's extremely unlikely that you'll see anything close to the maximum winds that the storm possesses. Of course, after a lot of heavy rain, you don't even need hurricane-force winds to knock down trees, cause structure damage, and create a very dangerous situation for those who are ill-prepared for such conditions.

[WeatherGuesser]

New Orleans levees can hold back a cat 3. Everything else will over top. They won't fail.

Levees hold back flooding and storm surge, not winds.

[KBBOCA]

Just a note about an interesting new resource. Bryan Norcross is now blogging at Wunderground.

http://www.wunderground.com/blog/bnorcross/show.html

[Weather Watcher]

New Orleans levees can hold back a cat 3. Everything else will over top. They won't fail.

Levees hold back flooding and storm surge, not winds.

Yes we know that!

[OzCycloneChaserTrav]

85 knots sustained =
98 miles an hour
157kmhr

Gusting too 105 knots =
121 miles an hour
194kmhr

If these figures from NHC are true, Isaac will be a damaging storm wind wise upon landfall too.

Wind speeds given by NHC in forcasts are MAXIMUM SUSTAINED winds. It is unusual to actually see those numbers unless you are right on the beachfront with winds coming from offshore. Of course, there are usually vortices and tornadoes in a landfalling hurricane that will have locally higher windspeeds a little inland as well.
With that being said however, you could easily see some 80-85+ sustained with higher gusts in a storm labeled 100 mph.
But yes, if it reaches the forecast intensity, there will be a lot of wind damage as well.

Personal Forecast Disclaimer:
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

Yeah of course, friction really plays a part in wind speeds below 10m once you
Move a few hundred meters away from a beach front or open area.
My main point though is, once you get nearly 100 mile per hour sustained winds, the damage from wind is obviously going to also play a big factor in the damage. I don't think alot of people along the gulf coast are expecting a 100 mile an hour storm. The worst part is, is that Isaac will strengthen all the way till landfall.

I hope all who were in low lying areas evacuated.

[thatwhichisnt]

New Orleans levees can hold back a cat 3. Everything else will over top. They won't fail.

Levees hold back flooding and storm surge, not winds.

Well yeah, I know that lol. I figured everone knew I was talking about surge.

Sent from my HTC One X using Tapatalk 2

[monicaei]

Does anyone on here know what Grand Isle, La can expect in terms of surge? Media reporting 5-10 feet. There is a HUGE difference between 5 and 10 feet.

[Countrygirl911]

Now they perdicting a cat 2 at land fall my weather people here is showing in my area for tuesday night into wendsday morning sustained winds of 30 to 40 mph gusts of 40 to 50 mph widespread trees and light poles down, trees on homes, electricity out and tornados this does not include wendsday night on. i live in SW MS and they perdict a cat 1 over me. i live in the woods and in a trailor i will be leaving to go to my mos next door or somewhere else will decide when husband comes home

[cheezyWXguy]

New Orleans levees can hold back a cat 3. Everything else will over top. They won't fail.

Levees hold back flooding and storm surge, not winds.

Yes we know that!

the saffir simpson scale is a windscale and has nothing to do with surge potential, so it would be irrelevant to say what category it is when mentioning how well equipped the levees are with storm surge. that is why he made that comment

[Blinhart]

Thanks for clarifying. I was wondering if it would be possible for winds to continue to strengthen after landfall in a system where winds take a long time to catch up to the MB drops as appears to be happening in this storm. Anyone know if it works that way? For example, if Isaac dropped 10 MBs in the hours right before landfall would it be possible that the winds would react AFTER landfall?

It isn't common for this to happen, but since the projected area for landfall is barely even land, with all the water in there, it could take some time for it to lose its strength, and possibly continue strengthening. We have seen some storms strengthen a good distance in land. If I remember Alyson actually could of been a Hurricane over Oklahoma, even though she made land fall as a Tropical Storm.

[Sambucol]

First day back at school, so I haven't had any access to news about Isaac. Is there any chance Isaac will move into SE TX/LA area? Or are we protected by the high pressure still? Thanks.