ATL: ISAAC - Post-Tropical - Discussion

[flashflood]

Imagine this - Isaac is now more intense than Ernesto by 1 mbar and it hasn't even made it to hurricane strength yet. This storm will definitely go down in my book as one of the oddest storms I've tracked yet. And of course, it will be in the same list as Daniel from earlier this year!

That's true, a very odd storm indeed.

I remeber Ernesto came ashore lookin like a 1/2 hurricane, this looks like it may do the same, well at least for now. You never know what's going to happen espcially if it stalls.

[TheDreamTraveler]

i dont think 960 mb at landfall is out of the question now.

I was thinking the exact thing. Given it still has almost a full day left to strengthen. We'll just have to see how well it can maintain itself and if the winds can actually catch up to the pressure. Unless the storm continues to be hindered.

[jinftl]

To the folks who are going to experience Isaac in a stronger form, might be helpful to know that the Palm Beach Post has a lead article on their site called:

Did forecasters adequately warn this area about Isaac? by Opinion Staff

Palm Beach County and the Treasure Coast were out of Isaac’s “cone” well before the storm approached the Florida Keys. There was a tropical storm watch as far north as Jupiter Inlet, but the models were in ever-better agreement that the storm would cross the Keys going west-northwest, and head out into the Gulf of Mexico a good distance from Florida’s west coast.

So how bad could it be way over here on the east coast? Pretty bad, as it turned out.

There were tropical storm force gusts, but the rain was the real surprise. Even as the storm was hitting Key West on Sunday, there seemed to be nearly as much rain in Palm Beach County. Then, as the storm moved beyond Key West on Sunday evening and overnight, there was much, much more rain in Palm Beach County. And the rain didn’t stop on Monday. Into the afternoon, a long “snake” of heavy rain extended from Melbourne down to Miami, inundating areas just west of the coast. A curving swath of heavy rain also curled across the northern part of the state. Forecasters had predicted rain. And the official forecasts included the expectation that some of the storms “could produce heavy rain.”

The National Hurricane Center’s graphics also had warned that even though most of Florida was out of the cone, “The cone contains the probable path of the storm center but does not show the size of the storm. Hazardous conditions can occur outside of the cone.” Certainly Palm Beach County and the Treasure Coast experienced plenty of those “hazardous conditions outside of the cone” on Sunday and Monday.

But were we adequately warned?


Several readers have posted comments like the excerpt below:

Hi. I’m looking out my window; my house sits atop a tiny island that I hope remains above the water level as the afternoon progresses. It’s never been this deep and I’ve been in this location nearly a decade and a half. I did not anticipate this much water, nor did those nearby that I’ve discussed it with. I can’t say that I wasn’t warned; anyone who’s lived here for a while knows that tropical drenchers frequently bring extensive flooding.
I’d also appreciate some detailed local information regarding when to expect water levels to drop enough that I can get my car out of my driveway. Do we know when which canals and drainage areas will subside below street level again? I’d really like to let my boss know whether I’ll be able to make it to work tomorrow or not

[monicaei]

What would be the practical effects of a very low pressure (someone mentioned 960) TS? Beyond potential... Does pressure change any of the actual on the ground effects of a storm?

[wxwatcher1999]

not sure if its just my eyes but i was looking at the satelite and it looks more like a western movement the last few frames

[JamesCaneTracker]

L. Eye Character: Open in the south
M. Eye Shape & Diameter: Circular with a diameter of 28 nautical miles (32 statute miles)

Also with a Pressure of 979mb which we already knew from the Advisory...

[tolakram]

To the folks who are going to experience Isaac in a stronger form, might be helpful to know that the Palm Beach Post has a lead article on their site called:

Did forecasters adequately warn this area about Isaac? by Opinion Staff

An opinion piece, I wonder how much real reporting went into it?

[rainstorm]

What would be the practical effects of a very low pressure (someone mentioned 960) TS? Beyond potential... Does pressure change any of the actual on the ground effects of a storm?

let me explain it like this, if the NHC said a 100mph cane was making landfall, and in the process the pressure was rising from 970 to 980 the damage would be less than if the NHC said a 80 mph cane was making landfall while the pressure was going from 979 to 965.

[ColdFusion]

no need to concern yourself with a few frames of movement right now. it's all averaging out as foretasted. Now when its bearing down on you, that might be a more adequate time to watch each frame if you are close to being on either side of the eye.

not sure if its just my eyes but i was looking at the satelite and it looks more like a western movement the last few frames

[monicaei]

What would be the practical effects of a very low pressure (someone mentioned 960) TS? Beyond potential... Does pressure change any of the actual on the ground effects of a storm?

let me explain it like this, if the NHC said a 100mph cane was making landfall, and in the process the pressure was rising from 970 to 980 the damage would be less than if the NHC said a 80 mph cane was making landfall while the pressure was going from 979 to 965.

Damage from what? Surge? Wind? How is a 100mph storm less damaging than an 80mph storm if the angles and timing and track are identical and the pressure is the determining factor?

[TheDreamTraveler]

What would be the practical effects of a very low pressure (someone mentioned 960) TS? Beyond potential... Does pressure change any of the actual on the ground effects of a storm?

It all depends on the makeup of the storm and how it comes inland from a certain trajectory, i.e this case being a worst case scenario if it happens according to the models. A 960mb storm would be that of a weak category 3 hurricane, which would have stronger winds, storm surge, and rain. So the actual on the ground effects would be greater given the stronger pressure gradient of the storm.

[rainstorm]

What would be the practical effects of a very low pressure (someone mentioned 960) TS? Beyond potential... Does pressure change any of the actual on the ground effects of a storm?

let me explain it like this, if the NHC said a 100mph cane was making landfall, and in the process the pressure was rising from 970 to 980 the damage would be less than if the NHC said a 80 mph cane was making landfall while the pressure was going from 979 to 965.

Damage from what? Surge? Wind?

both.

[smw1981]

not sure if its just my eyes but i was looking at the satelite and it looks more like a western movement the last few frames

Of course it does!

I haven't looked, but wobbles happen...don't worry about each wobble, focus on the way he is moving overall. And no, he is not going to Texas.. (at least not as of right now..)

[Jake8898]

Current IR satellite imagery continues to show relatively unimpressive structure. As we've seen through the past 36 hours, there is intense convection in only ~1/2 of the circulation. Yesterday, it's was primarily located in the northwestern 1/2 of the storm. This morning, most of the convection was "lop-sided" to the western 1/2 of the circulation. As of the latest image I've seen, nearly all of the precipitation is located in the southern semicircle. The upper-level anticyclone associated with Isaac is dislocated to the north of the center of circulation, resulting in some ~10 kt northeasterly shear over the center (and more over the western side of the storm). Although current precipitation water satellite data doesn't really suggest much in the way of dry air in the northern half of the storm, Isaac's appearance on satellite through the past couple of days certainly has shown signs of significant dry air entrainment.

So, the question is whether or not conditions will improve. Considering the warm water and "only" 10 kts of deep vertical wind shear, I would have expected to have seen appreciable intensification already if you had asked me a couple of days ago. However, the storm has looked "off" for the past few days, with strange wind structure as observed by recon (a few days ago, it was a very large area of weak winds near the center of circulation -- yesterday it was multiple eddies flying around). The structure of the winds around the circulation has improved and looks more "classic" now, but the lack of much convection in the northern semicircle doesn't bode well for significant intensification. I'm still waiting for the hammer to drop, so to say, and I'm waiting to see a symmetric blowup of convection around the center, but it's uncertain whether that will happen.

The longer Isaac stays in this 50-60 kt sfc peak wind state, the less time it has over water to intensify. Since I'd rather not see an intensifying hurricane slam into southeastern LA or coastal MS, this is probably a good thing. Landfall may not be that far off; each additional hour that recon flies through and sees only 55-60 kt surface winds is one less hour that intensification can occur. We can hope that Isaac maintains status quo of slow intensification and it makes landfall as a Cat 1. Considering the potentially "worst case scenario" track of putting New Orleans in the front right quad of the storm, this is much better than a major hurricane...

Plus, once this gets close to land, it's very likely that the eastern half of the cyclone will entrain dry continental air. It would not completely shock me if there are no measurements of sustained hurricane force winds anywhere when this thing makes landfall, even if it is classified as a hurricane at landfall (See Irene 2011 for an example).

From your lips to God's ears!

[monicaei]

let me explain it like this, if the NHC said a 100mph cane was making landfall, and in the process the pressure was rising from 970 to 980 the damage would be less than if the NHC said a 80 mph cane was making landfall while the pressure was going from 979 to 965.

Damage from what? Surge? Wind?[/quote]


both.[/quote]

How does an 80 mph storm do more wind damage than an 100 mph storm?

[rainstorm]

What would be the practical effects of a very low pressure (someone mentioned 960) TS? Beyond potential... Does pressure change any of the actual on the ground effects of a storm?

let me explain it like this, if the NHC said a 100mph cane was making landfall, and in the process the pressure was rising from 970 to 980 the damage would be less than if the NHC said a 80 mph cane was making landfall while the pressure was going from 979 to 965.

Damage from what? Surge? Wind? How is a 100mph storm less damaging than an 80mph storm if the angles and timing and track are identical and the pressure is the determining factor?

because a weakening storm at landfall doesnt get the winds down to the surface. you see it all the time. if a 100 mph cane is coming onshore while the pressure is rapidly rising before landfall winds on land will be far below 100 mph.

[6SpeedTA95]

let me explain it like this, if the NHC said a 100mph cane was making landfall, and in the process the pressure was rising from 970 to 980 the damage would be less than if the NHC said a 80 mph cane was making landfall while the pressure was going from 979 to 965.

Damage from what? Surge? Wind?

both.[/quote]

How does an 80 mph storm do more wind damage than an 100 mph storm?

Hurricane wind speeds are calculated using 1 minute averages. Weakening storms typically have lower gusts and a more steady wind pattern. So for example the wind speeds fluctuate between 90 and 105mph on a weakening cat 2. Or you have a strengthening cat 1 that may have a lot of 60mph winds and then a couple of quick but strong 110 or 120mph gusts within the convection around the eyewall.

[rainstorm]

let me explain it like this, if the NHC said a 100mph cane was making landfall, and in the process the pressure was rising from 970 to 980 the damage would be less than if the NHC said a 80 mph cane was making landfall while the pressure was going from 979 to 965.

Damage from what? Surge? Wind?

both.[/quote]

How does an 80 mph storm do more wind damage than an 100 mph storm?[/quote]

the 80 mph storm with the pressure rapidly dropping before landfall will have 80 mph winds and gusts in squalls will be above that

[monicaei]

let me explain it like this, if the NHC said a 100mph cane was making landfall, and in the process the pressure was rising from 970 to 980 the damage would be less than if the NHC said a 80 mph cane was making landfall while the pressure was going from 979 to 965.[/


the 80 mph storm with the pressure rapidly dropping before landfall will have 80 mph winds and gusts in squalls will be above that

But wouldn't the 100mph storm have winds of 100mph, sustained?

[pwrdog]

Dew points have risen to the NE of the storm... And are rising to the NW of the storm.. Might get going now from this point forward..

Those dry 62-65 dew points have been replaced by 72-77 DT's..