why did the winds weaken?

[recmod]

Looking at the Hurricane's structure, it is clear that thee is no ERC underway. The existing eye remains large and well-formed. If an ERC was beginning, the eye would be gradually shrinking until it collapsed completely, allowing a new larger outer eyewall to form....this is simply not happening at the present time.

I don't think the hurricane has actually weakened at all (as evidenced by the continued lowering central pressure). As the NHC expressed in the 5pm advisory, it appears Katrina has not mixed down the flight level measured winds at the normal ratio to the surface. Another possibility is the fact that recon only samples a very small portion of a hurricane's circulation in any single flight pass. It is highly possible that the dropsondes and other measuring equipment might have missed the highest sustained winds on their latest mission.

I find it hard to believe that anyone would think Katrina is in a downward trend intensity wise with a continually falling pressure. Also, the most recent IR satellite pictures show the high coldest cloud tops (the "reds" in the sat image) are beginning to return. If anything, I think Katrina COULD have a small UPWARD spike in intensity during the overnight diurnal maximum.

Nothing suggests a weakening trend.

Also, the hurricane's track is returning to a worst-case scenario for New Orleans. The models that had trended ever-so-slightly to the east earlier today have moved back west. Weather officials had hoped Katrina would not reach 90Longitude. That is the critical turning point for New Orleans.
Well, at 5pm, she is now at 89.0 and still chugging NW. Unless we see an almost immediate veer northward, this hurricane will cross 90W and come in almost directly over the city of New Orleans.

God Bless the poor people who have not been able to evacuate.

--Lou

[PuertoRicoLibre]

" DATA FROM THE STEPPED-FREQUENCY MICROWAVE RADIOMETER INSTRUMENT ON BOARD THE AIRCRAFT SUGGEST THAT THE SURFACE TO 700 MB FLIGHT LEVEL WIND RATIO IS NOT QUITE AS LARGE AS WE TYPICALLY USE...AND THE INITIAL INTENSITY IS ADJUSTED SLIGHTLY TO 145 KT."


This statement suggests to me that they may have over estimated surface winds at 2 pm and that this has nothing to do with ERC to anything else. If the pressure has gone down to 902 mb from 906, it means the storm has strenghtened. At least it has not gone down from 902 mb (the 2 pm reading) so it may be on a steady as she goes pattern. But if it indeed will move towards warmer water (can someone verify this?) then the 175 mph number may come back soon, this time as a real number.

[Mac]

I also do not think she is annular YET, although I believe she is trying to become annular. She doesn't have that classic donut shape of annular hurricanes yet, but I think it's interesting that her eye went from 29 nm to 33 nm in an advisory period. Usually, eye diameter goes the other way. But when hurricanes go annular the eye increases in diameter. So she could either be trying to become annular, or it could have been inaccurate eye diameter measurements.

The bad news about it going annular is that it would increase the width of the path of greatest destruction. The most powerful winds are only located in a narrow band immediately around the eye. But because an annular hurricane has a much wider eye, the width of destruction becomes equally broader. Imagine a 29 mile wide F3 to F4 tornado going through New Orleans. That's what we're talking about here. But this tornado isn't going to blow through in 15 minutes. It's going to blow for hours.

Let's hope she's not trying to become annular. The fact of the matter is though, that conditions are virtually perfect for her to do so between now and when she makes landfall, especially given the fact that she is heading into even warmer SSTs over the diurnal period. Simply put, this is not looking good folks.

[Brent]

I just don't think it was 175 mph earlier... so it really didn't weaken.

Of course... as Max Mayfield said a few minutes ago, the difference between 165 mph and 175 mph is the difference between being hit by an 18-wheeler and being hit by a freight train... neither one is good.

[jkt21787]

I just don't think it was 175 mph earlier... so it really didn't weaken.

Of course... as Max Mayfield said a few minutes ago, the difference between 165 mph and 175 mph is the difference between being hit by an 18-wheeler and being hit by a freight train... neither one is good.

Mayfield used that analogy with Dennis. Its time for a new one!

[krysof]

it's generally fluctuating, pressure 903, but Dr. Steve Lyons said the hurricane's strong winds are expanding.

[cjrciadt]

it's generally fluctuating, pressure 903, but Dr. Steve Lyons said the hurricane's strong winds are expanding.

Remember it only had 115 winds with 940mb pressure. That time the cane exploded in size not windspeed. Could it be doing that again?

[SouthFloridawx]

I didn't know that 165 MPH is weak. A storm of this magnitude is something that you do not see too many times in your life. It's number 4 in pressure 902 MB.

[M_0331]

Per Annular research, the eye size 30nm vs typical 6-8nm, the storm going annular. I may miss read the research, but looks annular. METS are the only one's that can confirm movement toward annular.

Eddie

[krysof]

that's possible, expanding then strenghtening again, remember waters ahead of it are the warmest waters it will encounter, no shear, the trough may be slightly impinging it.

[Mac]

Per Annular research, the eye size 30nm vs typical 6-8nm, the storm going annular. I may miss read the research, but looks annular. METS are the only one's that can confirm movement toward annular.

Eddie

Well, I am most definitely not a professional met. But I have read quite a bit about annular hurricanes because I found the phenomenon rather interest.

As I understand it, there is much more involved in a hurricane becoming annular than merely the size of its eye. It is the size of the eye relative to the windfield, among other things. I honestly don't think she's annular just yet, although I think she's heading in that direction.

And a 33 nm eye, while huge, is not alone an indication of it being annular. But I would agree with you that the professional mets are much more qualified than I to make such determinations.

[StrongWind]

Let's hope she's not trying to become annular. The fact of the matter is though, that conditions are virtually perfect for her to do so between now and when she makes landfall, especially given the fact that she is heading into even warmer SSTs over the diurnal period. Simply put, this is not looking good folks.

I have a vague idea of what annular is (ie. perfect donut shape) but what would it take for K to become one. Is there a certain wind speed/pressure? Or is it strictly defind by shape? Thanks.

[Mac]

Let's hope she's not trying to become annular. The fact of the matter is though, that conditions are virtually perfect for her to do so between now and when she makes landfall, especially given the fact that she is heading into even warmer SSTs over the diurnal period. Simply put, this is not looking good folks.

I have a vague idea of what annular is (ie. perfect donut shape) but what would it take for K to become one. Is there a certain wind speed/pressure? Or is it strictly defind by shape? Thanks.

I guess annular IS technically defined by the shape. The hurricane looks like a big donut, with the eye disproportionally large compared to the overall wind field. In order for it to occur, the storm has to be tremendously strong AND stable, AND in virtually perfect conditions. One the hurricane achieves annular status, it is capable of maintaining extreme intensity for extended periods of time, as it is not subject to the ERCs which non-annular hurricanes more frequently undergo.

[Mac]

And immediately after typing my last post, I checked visible and satelite images. Unless my eyes are deceiving me, that eye just got bigger between the last two sat images. If it was already annular, I wouldn't expect to see that happen. But it is further evidence, IMHO, that she is trying to achieve annular status.

She's such an attention hog.

[M_0331]

I agree the eye size is only one of many details that determine annular.
Usually, the PHD METS put out a journal paper months after the storm to state if storm was annular or not. God hope is not going annular.

Eddie

[krysof]

what's annular and is that bad?

[Mac]

Annular is very bad. The hurricane will literally appear to be a donut shape. The eye becomes very large compared to the overall circulation. It is generally considered a sign that conditions are perfect for a hurricane to maintain extreme intensity for extended periods of time, and the larger eye = wider path of maximum destruction.

[M_0331]

Annular hurricane:

http://www.ssec.wisc.edu/~kossin/articl ... arhurr.pdf

Semper Fi Eddie

[StrongWind]

Let's hope she's not trying to become annular. The fact of the matter is though, that conditions are virtually perfect for her to do so between now and when she makes landfall, especially given the fact that she is heading into even warmer SSTs over the diurnal period. Simply put, this is not looking good folks.

I have a vague idea of what annular is (ie. perfect donut shape) but what would it take for K to become one. Is there a certain wind speed/pressure? Or is it strictly defind by shape? Thanks.

[Mac]

Let's hope she's not trying to become annular. The fact of the matter is though, that conditions are virtually perfect for her to do so between now and when she makes landfall, especially given the fact that she is heading into even warmer SSTs over the diurnal period. Simply put, this is not looking good folks.

I have a vague idea of what annular is (ie. perfect donut shape) but what would it take for K to become one. Is there a certain wind speed/pressure? Or is it strictly defind by shape? Thanks.

There is no magic forumal for a hurricane becoming annular. There's no certain wind speed or pressure point at which a hurricane will become annular. Basically, it's the equivalent of all of the necessary ingredients falling into place at exactly the right time for the hurricane to take on an annular status--perfect SSTs, little to no shear, perfect outflow, no adverse interactions with other weather systems, etc. When all of these types of things happen at the exact same time, it allows a hurricane to become perfectly symmetrical--perfectly powerful. And it is able to maintain that power for a very long period of time. The one thing that may work against Katrina at this point is her interaction with land, which is beginning as we speak.