Re: Is Dean becoming annular?

August 19, 2007

(I tried posting this as a comment to Brendan’s post, but it got flagged as spam, so I’ll repeat it here and throw in a couple of references for the meteorologically inclined)

One of the things to come out of the recent research into annual hurricanes is an Annular Hurricane Index, which screens storms for the possibility of being annular and then rates how annular they are.  It’s being operationally tested this year.

And yes, yesterday evening, it did pass all of the screening steps and was marginally annualar, according to the index.

One thing that I didn’t realize when I wrote the Katrina post is that (based on observation), there is a max SST for a hurricane to be annular. The screening step for the index fails a storm if it’s over 29.1 C. Dean will be over waters warmer than that today.


Operational Implementation of an Objective Annular Hurricane Index (Powerpoint presentation)

 Annular Hurricanes (PDF)

What are Annular Hurricanes? (PDF)


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