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What is an annular hurricane?

What is an annular hurricane?
Posted at 10:45 PM, Sep 06, 2021
and last updated 2021-09-06 22:45:40-04

Hurricane Larry become a major hurricane over the holiday weekend. Not only did it achieve Category 3 status, it also achieved something that you don't normally see. The storm began exhibiting characteristics of an annular hurricane. Annular hurricanes are known for their large size, symmetrical appearance and large eyes. Larry's eye at one point was nearly 80 miles in diameter!

Annular hurricanes exhibit unique features that most other hurricanes don't have. A large symmetrical central dense overcast, a thick eyewall, both of which give it a truck tire the appearance of a large bagel or donut. They don't have any feeder bands, so the large ring of clouds around the eye IS the actual hurricane. They have large and symmetrical eyes over 50 miles across. They also tend to be more resilient in the face of hostile conditions like dry air and wind shear. Annular hurricanes don't weaken as quickly as other hurricanes, and this often times leads to large errors in intensity forecasts because it is difficult to forecast how rapidly they will weaken.

There is ongoing research on how annular hurricanes form, but conditions that are know to favor the development of annular hurricanes only exists around 3% of the time. Annular hurricanes tend to have a more broad wind field and are steady state in their intensity. More intense hurricanes tend to have very small "pinhole" eyes and a smaller RMW or radius of maximum winds.

There are three hurricanes that have impacted Florida in recent memory that exhibited annular features. Hurricanes Frances & Jeanne in 2004 and Wilma in 2005.