Hurricanes: The Greatest Storms

Last year the Storage Two blog highlighted all sorts of spooky science during the month of October. I was searching for more eerie topics and realized there is one very relevant and indeed, often frightening subject to explore: Hurricanes. The hurricane season officially runs between June 1 and November 30. Autumn is a particularly fertile time for hurricanes, and this season is extra deadly. 1,111 people have died due to hurricanes as of October 9, making 2016 the deadliest hurricane year since 2005.


What is a hurricane?

Hurricanes are rotating spirals of low-pressure thunderstorms circulating around a central eye. The name “hurricane” is only given to storms that form over the Atlantic or eastern Pacific Oceans. Similar storms that form elsewhere are called tropical cyclones or typhoons. Hurricanes are some of the most destructive natural weather events in the world. They can have diameters of 20 – 40 miles, able to wreak a wide swath of destruction when they make landfall.


How do hurricanes form?

Hurricanes need the heat and humidity of tropical ocean waters to coalesce. In pre-hurricane conditions, warm moist air rises away from the surface of the water, leaving lower air pressure below. Cooler air from the edge of the growing storm system is pulled in by this lower pressure, then heats and rises in an increasing cycle. Cool air continues to swirl in, be warmed, and rise, carrying moisture upwards into the atmosphere. As the air cools at higher altitudes, the moisture condenses into clouds.

As this process continues the clouds grow steadily larger. The wind begins to circulate around a round center, like water swirling down a drain. This column of air and clouds can pick up more thunderstorm clouds along the way. This sort of weather event is called a tropical disturbance.

As the thunderstorm gets bigger and higher, heat given off by the rising air becomes more pronounced. This causes an increase in air pressure around the top of the clouds, which forces wind to blow away from the high pressure areas. More cool air blows in down below, turns into warm air, and blows away up top. The storm whips even faster. When wind speeds hit 25 mph, the storm is classified as a tropical depression. 

As the storm builds in strength, its twisting nature increases. The storm rotates around a central eye, counterclockwise if the storm forms in the northern hemisphere and clockwise in the southern. When the wind speed reaches 39 miles per hours, the storm is classified as a tropical storm. When it hits 74 mph, the storm becomes a hurricane. Hurricanes are ranked into further categories depending on wind speed, with category 5 hurricanes having wind speeds of 157 mph or higher, capable of catastrophic damage should they reach land.


 Image by Ian Mackenzie

Image by Ian Mackenzie

Hurricane dangers

Wind

The most obvious danger of a hurricane is the wind. Wind alone can destroy poorly constructed buildings and mobile homes. Items blown by wind like signs and housing material become deadly missiles. Fallen utility poles and trees can crush houses, cars, and people.

Seeking shelter in a high rise building may seem like a good idea during a hurricane, but it is actually very dangerous. Wind speed in a hurricane increases with height, leading to shattered windows and other damages. Research suggests that to avoid the worst winds, you should stay on the tenth floor or lower during a hurricane. Just make sure to stay above flood levels!

Though wind speed begins to sharply decrease after the storm has been over land for about 12 hours, it can still remain very forceful. When Hurricane Hugo (1989) reached Charlotte, North Carolina (175 miles inland) it still had gusts of nearly 100 mph.

Storm Surge

Sometimes it isn’t wind that does the most damage during a hurricane, it’s water. A storm surge is an abnormal increase in sea level caused by stormy conditions. Though a hurricane’s low pressure contributes to a storm surge, it’s mostly the wind that does the job. The fierce winds of a hurricane blow in a circular direction around the eye of the storm. When a hurricane is over the ocean, water is churned in a vertical column. However, when the storm reaches shallow waters around land, the vertical circulation becomes disrupted. The water is unable to go down, so it is pushed inland instead.

Storm surges don’t come with a sudden wall of water like a tsunami, but they are still devastatingly fast. Waters can rise several feet over the course of minutes, quickly cutting off escape for victims. Many coastal highways are only a few feet above sea level and it only takes a foot of water to sweep a car off the road. People who ignored initial evacuation orders are often swept away when they try to flee an oncoming storm surge.

Hurricane Katrina, a category 3 storm, produced a storm surge of 28 feet. There are many factors that determine the height of a storm surge, but even category 1 hurricanes can produce lethal 10 ft surges. Storm surges can easily destroy houses, erode the foundations of coastal highways, and lay waste to harbors.

 

Tornadoes

Hurricanes are dangerous enough on their own, but some also produce tornadoes. These tornadoes don’t generally match the ferocity of those seen in the Great Plains, but they can still produce substantial damage. Tornadoes originating from hurricanes don’t usually come with the usual tornado warning signs, like hail, so can take people by surprise.


Hurricanes and Climate Change

As I write this, there are still thousands of people in the United States and elsewhere recovering from Hurricane Matthew. There were many unluckier still. 21 people have died so far in the United States and over a thousand in Haiti. These numbers will only rise as floodwaters and power outages persist. Hurricanes are terrible disasters, and they’re going to get worse if climate change continues.

Hurricanes thrive on warm oceans. As the Earth grows warmer, the oceans warm too. Since the 1970s, the destructiveness of hurricanes has doubled. It isn’t that there are more hurricanes, but that the hurricanes are growing stronger. Given the cost of rebuilding after hurricanes and the deaths they incur, future populations may choose to move away from the shores. Unfortunately, moving isn’t an option for many poorer areas and island nations.  Somehow, we’ll all have to find ways to adapt to the changing weather of our future. 

- Kate Dzikiewicz, Paul Griswold Howes Fellow