Let's talk about annular 'canes...

[senorpepr]

There has been a lot of talk about annular hurricanes this year.

This is from Wikipedia.

Annular hurricanes have a large, symmetric eye surrounded by a ring of intense convection, with hardly any convection (i.e. bands) elsewhere. These types of storms are not prone to fluctuations in intensity related to the eyewall replacement cycles typically seen in intense tropical cyclones.

Statistics show that forecasters significantly underestimate the wind velocities following the time when the hurricane peaks. The errors occur because this type of hurricane maintains intensity longer than usual.

Less than 1% of Atlantic cyclones exhibit annular characteristics.

[Droop12]

Glad someone finally posted the right definition. It seems everyone is quick to label every major hurricane "annular". Perfect example of this would be Isabel. Other than that, I cant think of any other hurricanes in the past year that fit the description. Thanks for the info Senorpepr.

[NCHurricane]

These types of storms are not prone to fluctuations in intensity related to the eyewall replacement cycles typically seen in intense tropical cyclones.

This line would suggest that Katrina was not annular, or did it decline from an annular state? It was going through an ERC at landfall, correct?

Chuck
http://www.nchurricane.com

[WxGuy1]

Knaff, Kossin, and DeMaria, 2003: Annular Hurricanes. Wea. and For. --> http://www.ssec.wisc.edu/~kossin/articl ... arhurr.pdf

An annular hurricane is identified if the hurricane persists
for at least 3 h in an axisymmetric state defined by the following: 1) the hurricane has a normal-to-large-sized circular eye surrounded by a single band of deep convection containing the inner-core region and 2) the hurricane has little or no convective activity beyond this annulus of convection.

The evidence presented here suggests that annular hurricane formation is preceded by a dramatic asymmetric mixing event in which possible mesovortices mix eyewall air into the eye and vice versa, as shown in Fig. 4, culminating in the formation of the axisymmetric storms with large eyes (i.e., annular hurricanes). The observed thermodynamic structures of two storms sampled by aircraft (Luis and Dora) as characterized by more uniformly distributed values of ue in the eye suggestthat a dramatic horizontal mixing event had recently occurred. At the same time the observed wind field suggests that some eye-to-eyewall mixing is still occurring, as shown by the steplike features in the tangential wind that are associated with local vorticity and angular velocity peaks.

In their study, they found 6 hurricanes in the 1995-1999 seasons that were annular. That's a pretty good read if you want to learn more about annular hurricanes.

EDIT: Not sure if Katrina was technically annular, but it was VERY close. The CDO was incredibly symmetric and lasted quite a while.

[Droop12]

I dont think Katrina was ever Annular. She was always a very large storm, with a large eye but had vast amounts of outer rain bands and not not just a solid inner core like Isabel.

[Buck]

Katrina and Rita were botha annular at one point, I thought? Wilma didn't quite get there... nor did Emily.

[superfly]

Rita was never annular, Katrina was in my opinion.

[superfly]

I dont think Katrina was ever Annular. She was always a very large storm, with a large eye but had vast amounts of outer rain bands and not not just a solid inner core like Isabel.

Certainly not as pretty as Isabel was but there were very little feeder bands when Katrina was a cat 5.

[NCHurricane]

Bumping up because this is could be a very good debate.

Chuck
http://www.nchurricane.com

[FloridaHawk82]

Was Andrew Annular? I've seen people mention that it was.

[quandary]

Was Andrew Annular? I've seen people mention that it was.

No Andrew as in no way annular. It was a small intense storm with a pinhole eye.

[quandary]

Also, the strongest hurricanes are not annular, or so it would seem. According to the report, the annular hurricanes observed were Luis, Eduardo, Dora, Howard, Darby and... I can't remember the last one.

Eduardo was the strongest storm of 1996 and Luis was a 145mph hurricane too. However, the strongest storms of 1995-1999 were not on this list.

Strongest storms of this period:
Linda (WPAC, 1997) 902mb 185mph winds
Mitch (Atlantic, 1998) 905mb 180mph winds
Opal (Atlantic, 1995) 918mb 155mph winds
Floyd (Atlantic, 1999) 921mb 155mph winds

Outside of these storms, there were also Atlantic storms:
Georges (155mph, 1998), Lenny (155mph, 1999), Gert (150mph, 1999)

None of these storms would be annular, but they were the strongest storms of the period. Isabel (2003, 165mph, 916mb) is the strongest annular storm of recent times. Stronger storms, Katrina, Rita, Wilma and Ivan, were not annular. Annular storms just aren't that strong.

[quandary]

Katrina and Rita were botha annular at one point, I thought? Wilma didn't quite get there... nor did Emily.

I just don't think that annular hurricanes are all that anymore (for a basis for the opinion, see the post with all the strongest storms of 1995-1999. Its probably not accurate to say that they didn't "get there," as if this was a nirvana for hurricanes to reach. Also, Gilbert was not annular, Allen certainly wasn't with its endless ERCs and the FL Keys storm wasn't since it was so small (same for Camille).

[alicia-w]

According to a 2003 paper, the following are annular hurricanes:

http://www.ssec.wisc.edu/~kossin/articles/annularhurr.pdf

Luis, 1995 Atlantic, 120–125kts
Edouard, 1996 Atlantic,120–125kts
Darby, 1998 East Pacific, 90–100kts
Howard, 1998 East Pacific, 115–85kts
Beatriz, 1999, East Pacific, 100–105
Dora, 1999 East Pacific, 80-95kts

Several of those look like fairly strong storms to me.

[WxGuy1]

Annular storms just aren't that strong.

I'm not sure you can reach that conclusion. The publication found that annunar hurricanes in the 1995-1999 period had an average intensity of about 85% of the MPI (Maximum Potential Intensity), compared to all hurricanes, which had intensities averaging about 42% of their MPI. The annular hurricanes had an average intensity of 107kts, so I wouldn't say that they "just aren't that strong". They may not be THE strongest storms, but that's still borderline Cat 3/4.

In their sample, they found 17 hurricanes which had annular characteristics, but did not meet their definition of annular for one reason of another. Some of the storms you mentioned fell in this group. Read page 218 and look at Table 6 in that paper.

[alicia-w]

actually table 6 is on page 220

[Normandy]

Was Andrew Annular? I've seen people mention that it was.

No Andrew as in no way annular. It was a small intense storm with a pinhole eye.

Andrew didnt have a pinhole eye....look at a satellite pic of it.

[WxGuy1]

actually table 6 is on page 220

That's why I said "Read page 218 AND look at Table 7"...

[clueless newbie]

Glad someone finally posted the right definition. It seems everyone is quick to label every major hurricane "annular". Perfect example of this would be Isabel. Other than that, I cant think of any other hurricanes in the past year that fit the description. Thanks for the info Senorpepr.

I think Kate (of the same year) was annular as well. Maybe Alex for a moment?

Annular canes seem to extract energy more efficiently from relatively cool waters. Note that typical annular canes dont have very cold convection. HIgh water temperatures promote strong convection that tends to disrupt the organisation of an annular hurricane/prevents its formation.

At least as I see it....

[alicia-w]

actually table 6 is on page 220

That's why I said "Read page 218 AND look at Table 7"...

actually, you didnt.