Every year, beginning around the end of August and continuing into November, North America anxiously endures hurricane season. Hurricanes form in the tropical Atlantic Ocean and track westward towards the Caribbean, Gulf of Mexico and mainland United States. The wind speeds in strong hurricanes rival those in most tornadoes, and can cause massive destruction over very large areas. However, it is the flooding from these storms that causes the most destruction and loss of life. Harvey dropped many trillions of litres of rainwater, which is enough to raise the water level of all five Great Lakes by a foot. The atmospheric conditions within hurricanes also cause the ocean surface to heave upwards, creating a dangerous wall of water called a storm surge. The combination of dangerous winds and widespread flooding combine to make hurricanes nature’s most powerful and destructive show of force.
First it was Harvey, now it’s Irma – this year’s Atlantic hurricane season is shaping up to be an especially bad one. Is there a link between rising global temperatures and the strength and severity of hurricanes? Should we expect more storms like Harvey in the future?
In short, yes.
Hurricanes form over warm water – the warmer the water, the more the they can intensify. Also, warmer air can hold more water vapour, so higher temperatures increase the potential for flooding rains.
But (there’s always a but):
As is the case for severe thunderstorms and tornadoes, climatologists are not certain whether the frequency of hurricanes will change in the coming decades. This is primarily because the conditions required for hurricane formation are complex, and it is not yet clear whether the frequency of these circumstances will increase.
Did you know? On January 10th 2016, tropical storm Alex was upgraded to a fully formed Category 1 hurricane. The occurrence of a hurricane in the middle of winter in the Atlantic is extremely rare, but the extraordinary rise in winter temperatures in the Northern Hemisphere means storms like Alex could become much more common.
Hurricanes are known for their driving winds and torrential rains. However, most of the immediate damage caused by a hurricane comes from the storm surge. A storm surge originates as an upward bulge in the sea surface caused by the extraordinarily low pressure found within a hurricane (think of how water moves up a straw, against the pull of gravity, when the air in the top part of the straw is sucked out). This surge is then made worse by the very strong winds blowing the water toward a coastline, where the shape of the coast can cause the water to rise even higher. And, if that wasn’t enough, the surge will be especially bad during high tide. These storm surges can be several meters tall – high enough to overflow seawalls and levees – and can cause flooding over a very wide area. Stronger hurricanes have lower central pressures and stronger winds and therefore create even more devastating surges.
Did you know? Hurricane Harvey was made worse because of Climate Change. August 2017 – Hurricane Harvey becomes the strongest tropical storm to hit the United States in over 60 years, bringing with it a record amount of rain. Climatologists have been quick to point out that while Harvey wasn’t caused by climate change, it was almost certainty made worse because of it (It’s a fact: climate change made Hurricane Harvey more deadly).
Most hurricanes never reach land. Winds high in the atmosphere continually try to pull Atlantic hurricanes to the right, into the North Atlantic, where they die off slowly over the colder water. However, changes in atmospheric circulation could impact this important natural process. Hurricane Sandy, which severely impacted New York City in 2012, made a very sudden left turn just hours before making landfall. The left turn was initiated by an unusual jet stream, which was largely caused by above average temperatures and below average pressures over Greenland (both predictable symptoms of a warming planet).
A Worrisome Development
As we write this blog, hurricane Irma is a Category 5 hurricane with sustained winds of 180 mph (290 kmh), making it the strongest hurricane ever recorded in the Atlantic outside of the Caribbean and the Gulf of Mexico. Its current trajectory puts Florida in its sights, as well as many vulnerable Caribbean islands. That is, it is looking like our American and Caribbean friends are going to be hit, yet again, with a life-threatening and costly storm.
- Hurricanes, Typhoons and Cyclones are just local names given to the same type of storm.
- Hurricanes in the Northern Hemisphere only spin counter-clockwise.
- Hurricanes are named from a pre-determined, alphabetical list. The list repeats every 7 years; however, the names of especially bad storms are removed from the list forever (e.g. Andrew, Katrina, Sandy, Harvey).
- Hurricanes can’t form near or over equator.
- Only three Category 5 hurricanes have hit the mainland United States in modern times.
- The strength of hurricanes is classified from 1 to 5, with 5 being the most intense. Only 32 Category 5 Atlantic hurricanes have ever been confirmed (Irma is the 32nd).
– Ryan Smith, Prairie Climate Centre
cover photo source: NASA