Question for Pro's and Am's alike.......

[Downdraft]

I thought I'd pose a question and let everyone take a shot at it. That way we all learn something. So the question I'm posing is this in three parts.

1.. What is an annular hurricane?

2. Why do the EWRC's (eye wall replacement cycles) occur less frequently than in a "regular" tropical cyclone.

3. What causes a system to become annular?

Okay, fair game for all go for it.

[Cyclone1]

An annular hurricane is a hurricane with a large eye, and minimal, to no rainbands. Just like a large ring of convection. Other than that, I don't think there is any difference from annular to typical besides the fact that annular storms can last longer of harsher conditions. (i.e. Epsilon.)

[Beam]

Annular hurricanes are the disc- or donut-shaped storms that feature a large eye, an intense ring of convection, perfectly symmetrical outflow, and little to no banding. They are essentially a perfect heat engine, and have no need for ERCs.

A classic annular hurricane would be Isabel of 2003, and another, more notable one, though it may be debatable, is Katrina of 2005. As to how and why they form, the only thing I've been able to observe is that they tend to happen over large areas of open water in low shear environments, and seem to appear in the late stage of an ERC in an already symmetrical and intense system, except a large, donut-hole eye appears where the outer eyewall is, rather than the outer eyewall replacing the inner one as is typical.

This is usually followed by rapid intensification, with much fewer fluctuations in strength due to the lack of ERC's and the near-perfect organization of the system. This, combined with the fact that the larger eyewall produces a greater radius of devastating winds and surge, makes an annular storm far more dangerous than a typical hurricane, if it can maintain that structure until landfall.

[Cyclone1]

Katrina wasn'r annular. It's large eye was certainly characteristic of an annular system, but other than that, it had no further annular characteristics. The best example I can think of is Epsilon. Large eye, no rainbands, kept a consistent strength for days.

Flossie is the most recent example of an annular major hurricane.

[Ptarmigan]

1.) Annular hurricanes are hurricanes with large eyes and no outer rainbands. They look like doughnuts and tend to be large. Hurricane Isabel is a good example of annular hurricane. Also, they maintain strengths longer than non-annular hurricanes. Hurricane Katrina had a large eye, but it is not an annular hurricane because it had large amount of rainbands.

2.) Annular hurricanes are nearly perfectly organized, so less likely for EWRC.

3.) That's debatable. Annular hurricanes/typhoons/tropical cyclones tend to occur more in the Pacific, where conditions are generally favorable than in the Atlantic.

[tolakram]

http://en.wikipedia.org/wiki/Annular_hurricane

Decent article.