Is she still annular?

[Jason Toft]

I read something earlier about Katrina being an annular storm, which, IIRC, means that there's a strong, symmetrical circle of deep convection surrounding the storm. My question is, is it still this way?

Thanks,
Jason

 

[Dustin Wilcox]

Indications from the 10pm CDT advisory are No, it appears that the SW side of the eye is lossing its symetric shape and indications are that a new more compact eye may be in the proccess of forming.

 

[Jeff Snyder]

typically, there is a weakening trend through the eyewall replacement cycle, sometimes followed by rapid strengthening. Therefore, this storm very well could drop into high-end Cat 3 range before landfall and not have enough time to restrengthen. The latest discussion from NHC certainly doesn't make it sound like they are very confident in their Cat 5 assessment right now. With evidence of concentric eyewalls and start of ERC, there's a chance that NO could dodge a catastrophic bullet tomorrow morning. Remember, the really strong SUSTAINED winds (>100mph) are probably only 15-20 miles outside the eyewall, with the Cat 4-5 winds probably within a few miles of the eyewall.

 

[Jeff Snyder]

In addition... latest VORTEX showing pressure is up to 908mb with the highest flight-level winds of "only" 122kts... That'd be like 110kt at the surface (cat 3 winds). If this is indeed the case (they may not have necessarily sampled all quads yet), then i can't imagine that we won't see cat 4 on the 1am intermediate advisory. 908mb is still massively deep, but the wind fields of Katrina are huge, so a <905mb pressure is probably needed to maintain pressure gradient forces strong enough to produce Cat 5 winds.

 

[Dustin Wilcox]

I am seeing evidence of that as well esspecially on doppler radar, but can find no evidence of weaking from the infared satelite picture it still shows large well formed eye wall.

 

[Jeff Snyder]

Chris, what's the typical timeline for eyewall replacement cycles? I know storms tend to weaken at through the ERC cycle, then may strengthen again after the process finishes. I'm just trying to figure out if the storm may be on the strengthening or weakening side in 8 hours...

 

[Anonymous]

The discussion also mentions that as an eyewall is being replaced the wind field generally expands...thus major category winds could cover a broader area, even though the cyclone may have lesser intensity at the landfall area.

 

[Brett Adair]

Trochidial Oscillations have began taking place once again nearing the end of this ERC. Last night when this happened, the eyewall went annular and significant strengthening began.

 

[Dustin Wilcox]

Are you hinting at the idea that we are near the end of this cycle?

 

[Brett Adair]

Are you hinting at the idea that we are near the end of this cycle?

We are nearing it, I do believe. More lightning now showing up in alot of live shots....given this imagery, the last hour the inner eyewall especially on the NE side is increasing in lightning activity.

 

[Michael Auker]

Trochidial Oscillations? Sounds interesting! Please explain?

 

[Brett Adair]

Trochidial Oscillations? Sounds interesting! Please explain?

These oscillations are what will lead you to believe that hurricane is beginning to move a different direction, such as north in this case. It is still moving slightly west of north, but these oscillations will actually circulate around the center and cause wobbling. A due north track will be evident within the next 3-6 hours. Water temperatures are cooling the further north you head towards the coast, not to mention the water is much more shallow. This may be in some ways a saving grace. Still not much to help New Orleans...

 

[Austin Ivey]

Water temperatures are cooling the further north you head towards the coast, not to mention the water is much more shallow. This may be in some ways a saving grace. Still not much to help New Orleans...

Brett, Given the image below how can you say h20 temps are cooler north toward the la coast. according to this noaa interpolation it seems h20 temps are actually significantly warmer (1-2C) along the LA coast than when katrina begin her turn north-west.

 

[Brett Adair]

Temperatures still may be warmer, but those charts lie quite a bit. Looking at the bouy data right now, I don't see one single bouy reporting over a 29C water temperature in the northern Gulf.

This is what caused Katrina to RAPIDLY intensify. Look at the depth of this latent heat pocket.

 

[Robert Dewey]

Yeah, I don't know about cooler, but definitely more shallow... Of interest, look at the warm waters just off the FL coast where Charlie struck last year! I wonder if that area of warm waters is what caused such rapid deepening of Charlie... Oh well, back to the topic.