What is an annular style of hurricane?

What is an annular hurricane?

An annular hurricane are usually some of the more intense cyclones that resemble a tire or a doughnut-like structure, with limited banding.

When most people think of powerful hurricanes or typhoons, they imagine an area of low pressure with an eye and spiraling rainbands, but not all cyclones look alike.

Some of the more powerful cyclones become what are known as annular tropical cyclones, which resemble a tire or a doughnut shape.

Researchers from Colorado State University were some of the first meteorologists to label hurricanes as being annular during the early 2000s.

Generally, the cyclones have a large symmetric eye, surrounded by intense convection, but lack significant banding features.

Typically, only a few cyclones reach this annular stage, and they are mostly in the upper echelons of being a major hurricane.

A hurricane reaches major status when winds reach at least 115 mph, making the cyclone a dangerous Category 3.

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Hurricane Iselle (2014) satellite photo

(NOAA)

Observers have noted that hurricanes tend to take on an annular look after they undergo what is known as an eyewall replacement cycle.

An eyewall replacement cycle is the natural process where a secondary eyewall forms and replaces the storm's original feature.

Usually, after an eyewall replacement cycle concludes, the cyclone gains a larger wind field and, in some cases, can become more powerful.

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An annular appearance typically means that a cyclone is resistant to environmental factors, such as dry air and hostile upper-level winds, which can help prolong a hurricane's lifespan.

Cyclones with banding features often provide the chance for dry air intrusion, which can quickly cause a hurricane to weaken and unravel.

Annular hurricanes are more common in the Pacific than in the Atlantic, where there is more open ocean for these monsters to roam.

According to previous studies, annular hurricanes are often difficult to forecast, with meteorologists often underestimating the strength of the cyclone.

Hurricane Linda, which formed in 2021 in the eastern Pacific and became a powerful Category 4 cyclone, is often considered to be an annular-type storm.

The cyclone formed off the coast of Mexico and was still an identifiable entity when it reached Hawaii - a more than 2,000-mile trip.

Hurricane Isabel, which formed in the Atlantic in 2003, is often considered to be an annular cyclone.

After strengthening into a Category 5 hurricane over the central Atlantic, the cyclone went on to make landfall as a Category 2 along the coast of North Carolina.

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It remains somewhat unknown as to why some hurricanes take on the annular appearance while others resemble giant spiraling bands, with some scientists crediting the size of the system's circulation and the available atmospheric ingredients.

Additionally, the annular look appears to most often occur during the second half of the season, when sea surface temperatures have either reached their peak or started their seasonal decline.

Hurricane Flossie (2013) satellite photo

(UW-CIMSS / FOX Weather)