The eye of a hurricane is a uniquely fascinating phenomenon. It’s hard to imagine that at the center of a vicious storm with 110 mph winds is an entirely calm circle of clear sky. What exactly is the eye of a hurricane? Why does it occur? And is there always just one?
Hurricanes and tropical storms rotate around the calm eye in the center of the storm. On average eyes are about 20 to 40 miles in diameter, but they can range in size from being just a couple of miles to a couple hundred miles in diameter. The more powerful the hurricane the smaller the eye tends to be.
If you’ve read hurricane survival tips on some of our past blogs or anywhere else on the internet, you may already be away of the danger the eye can pose. It’s not entirely uncommon for people in the eye of a hurricane to assume the storm has passed and think it’s safe to go outside.
People caught in the eye need to continue sheltering in place and, if anything, prepare for the worst. Circling the center eye are the eyewall winds, the strongest in the hurricane. In literal seconds you can pass from the relative calm of the eye into the 150-mph winds of the wall (depending on the strength of the storm). The experience of being in the eye of a hurricane is entirely different on the ocean. Water is literally being pushed in every direction from the colliding winds, generating massive 100 plus foot waves in the eye.
Eyes are complicated, and not all of what happens in them seems to be consistent.
When over the water the rotation of the eyewalls causes an updraft, pulling the warm air near the surface of the water up and around the top of the storm before it drops back down on the outer edges of the storm. This positive feedback loop fuels and strengthens a storm.
All the pressure pushing towards the center also sinks some of the air in the eye. At a certain point air being pushed downward plus the updraft equalizes, and eventually overpowers the updraft. This makes the eye warmer than the surrounding storm which contributes to the evaporation of clouds in the eye.
This diagram shows the relation between wind speed in the walls of a hurricane and the pressure in the eye – the pressure in the eye drops while the wind speed increases. Here’s another diagram that shows how descending air drops down in the eye while warm moist air spirals up and around the walls and pushes towards the edge of the storm.
Yes, and they can be formed in two different ways.
The far less common two-eyed hurricanes occur when two storms literally collide in what’s known as the Fujiwhara Effect. Hurricanes caught in the Fujiwhara Effect may not actually collide, but they will begin rotating around a common center.
Similarly sized storms are sometimes described as “dancing around” one another before they spin off in different direction. If one of the storms is significantly stronger than the other, it may pull the smaller hurricane in and eat it. While the smaller storm is being cannibalized it will appear as if the one big storm has two eyes. You can watch this short video from 10 Tampa Bay for some examples of what this looks like.
The other way a particularly intense hurricane (Category 3, 4 and 5) develops two eyes is during an eyewall replacement cycle:
During the process a storm weakens until the new eyewall is in place, at which point the storm will be back up to its pre-replacement strength.
The National Oceanic and Atmosphere Administration (NOAA) points to two examples of this: Hurricane Andrew in 1992 and Hurricane Allen in 1980. Hurricane Allen underwent eyewall replacement several times, during which it weakened to a Category 3 and then restrengthened to a Category 5 when replacement was complete.
Here’s a good picture of Hurricane Wilma (2005) off the coast of Georgia where you can clearly see two eyes at the center of the storm.
If you’re ever in a situation where you can’t or don’t want to evacuate from your Florida home during a hurricane watch, we hope you heed this warning. The eye may seem deceptively calm, but it’s important you stay indoors when it passes overhead. Stay safe!