The Hydrology of 2017’s Hurricanes

Recently the North American Continent and Caribbean Islands was ravaged by a series of violent hurricanes. The hurricanes that hit the U.S. typically start off as severe storms on the west coast of Africa. As the storm hits the ocean, it will gather strength by feeding off the warmth and moisture of the ocean. Then, thanks to the Coriolis Effect, it gains rotation.

The Coriolis Effect is a phenomenon that causes fluids and air to curve over the earth’s surface. This occurs because the earth is rotating on its axis from west to east and it spins faster where the sphere bulges, the equator. As the hurricane spins an area of high pressure is created up top and low pressure on the bottom. The whole thing rotates around the eye of the storm.

The storm’s eye forms as air rotates up and out of the hurricane and back in again. This keeps the eye clear. The most dangerous part of a hurricane is the eye wall. This is the area with the highest wind speeds.

Hurricanes need warm water to form, at least 79 degrees Fahrenheit. They need open water, hurricanes die once they hit land as moisture no longer can feed the storm. The final thing they need is high pressure above it. Wind shear kills the storm. Once the storm forms it crosses the Atlantic, and either dies out or hits the coast. With terrifying winds add in storm surge they can become very dangerous.

This year NOAA forecasted 14 to 19 named storms and 5 to 9 named hurricanes. As of this paper at least five named hurricanes occurred, Irma, Harvey, Jose, Katia, and Maria. Of those five, four made the news killing people, Irma, Harvey, Maria, and Katia. Three struck the United States, Harvey, Irma, and Maria. Those last three will be the focus of this paper.

Hurricane Harvey was one of the costliest storms we have had to date. This category 4 storm hit Texas well “like a hurricane.” The hurricane was boosted by unusual climate conditions, the Gulf being 2.7 to 7.2 degrees hotter than historical averages for this time of year. This heated water fuelled the storm. This added moisture created record flooding.

In some parts of Houston there was 50 inches of rainfall. New Orleans’s Hurricane Katrina only had 10 inches of rain. The devastation ended up killing 60 people. Despite all the damage done Harvey was quickly eclipsed by hurricane Irma.

Hurricane Irma was a category 5 storm. The storm was roughly 800 miles wide with sustained winds of 185 mph and gusts of 200 mph. Harvey was large and horrific but Irma came close to reaching its full potential or theoretical maximum intensity.

How did this hurricane get so strong? According to Kerry Emanuel quoted on Wired.com “Hurricane Irma: The Impossible Storm” the storm had perfect conditions. It had a warm deep layer of water, and almost no wind shear. This combo let the storm become deadly.

Others point out that both storms are obvious indicators of climate change. After all in 1990 Harvey would have been a 500 year storm, today’s climate conditions, it’s a 15 year storm. Irma like Harvey hit the US coast as a category 4 hurricane. Two category 4 storms within weeks of each other is practically unprecedented the last occurrence being in 1954.

While Irma finished destroying the Islands and wiping out Barbados, Maria builds in behind it going from a category 1 to a category 5 in less than a day. Maria hit the Dominica in full strength and Puerto Rico as a category 4. Neither island had seen a storm of this magnitude in almost 100 years.

While the scientist claim tagging these events as global warming is tricky there is no denying the warmer water of the Atlantic and Gulf this year strengthened hurricanes. The National Geographic states that with warming oceans high intensity hurricanes will increase. Scientists agree the record breaking rain fall for Harvey was in fact climate change. The impact of the 50 inches rainfall being billions in damage, millions dislocated and 60 deaths.

For Florida hurricane Irma’s 200 mph winds were an issue. The buildings were built to withstand category 5 winds of 185 mph. With gusts stronger than that buildings could give easily. The storm surge would flood coastal areas. With the sea already rising Irma compounded Florida’s battle with the ocean.

Hurricane Irma’s devastation wrought a human toll, wiping out a 300-year-old civilization on Barbuda. 73 total died in the U.S. and Caribbean from Irma. For the Caribbean they scarcely cleaned up Irma when Maria blew through.

Maria was the worst storm to make a full on hit for Puerto Rico in 80 years. The storm barrelled toward the Dominica at 175 mph as a hurricane 5. Fuelled by the warm Atlantic waters this storm became devastating quickly. The storm rained down 30 inches in some parts of Puerto Rico and at least 6 people died. These rains brought about catastrophic flash flooding where water got trapped in mountain streams.

The geography of Puerto Rico affected the damage sustained. The eye wall bounced off the mountainous landscape rather than ploughing straight through slowing the storm causing it to dump more rain. It also caused massive damage to areas it would not have if it had passed straight over. On top of this some areas got almost 9 feet of storm surge, but in this regard the mountains buffered the surge.

The storms have left many displaced and the government scrambling to fund aid for all those effected. People who fled Irma ended up stranded on Puerto Rico. The island, as of this writing, is still recovering and many places are without power or phone service.

Thankfully for Puerto Rico and the rest of the area these major storms should have cooled the waters meaning that perhaps any other hurricanes this season won’t be able to gain strength. This season it appears to have been an unusual one. What caused this?

In the intro we discussed that hurricanes needed two things. Warm open oceans, and high pressure. This year the waters were warmer than average and on top of that a record rise in sea levels increased storm surges. Stationary weather, due in part to climate change, caused Harvey to move at 3 mph over Texas prolonging rainfall. These storms were deadly because the conditions were right just right.


Bibliography

• Elements of physical hydrology. (2014). Baltimore: Johns Hopkins University Press.
• Hurricane Irma’s Death Toll Now 73; 10th Hollywood, Florida, Nursing Home Victim Confirmed. (2017, September 14). Retrieved October 09, 2017, from https://weather.com/storms/hurricane/news/irma-aftermath-keys-caribbean-florida
• Little, B. (2017, September 06). Why Hurricane Harvey is Poised to Become America’s Costliest Storm. Retrieved October 09, 2017, from http://www.history.com/news/why-harvey-is-likely-the-most-expensive-hurricane-for-now
• Resnick, B. (2017, September 21). Why Hurricane Maria is such a nightmare for Puerto Rico. Retrieved October 09, 2017, from https://www.vox.com/science-and-health/2017/9/21/16345176/hurricane-maria-2017-puerto-rico-san-juan-meteorology-wind-rain-power
• Roberts, D. (2017, August 28). Climate change did not “cause” Harvey or Irma, but it’s a huge part of the story. Retrieved October 09, 2017, from https://www.vox.com/energy-and-environment/2017/8/28/16213268/harvey-climate-change
• Rodgers, A. (2017, September 07). Hurricane Irma: A Practically Impossible Storm. Retrieved October 09, 2017, from https://www.wired.com/story/hurricane-irma-a-practically-impossible-storm/
• Rothschild, A. (2014, January 09). The Coriolis Effect. Retrieved October 09, 2017, from http://www.pbs.org/wgbh/nova/earth/coriolis-effect.html
• Why This Hurricane Season Has Been So Catastrophic. (2017, October 02). Retrieved October 09, 2017, from http://news.nationalgeographic.com/2017/09/hurricane-irma-harvey-season-climate-change-weather/
• Yan, H., & McKirdy, E. (2017, September 20). Puerto Rico governor: Still time to get to shelter before Maria hits. Retrieved October 09, 2017, from http://www.cnn.com/2017/09/19/americas/hurricane-maria-caribbean-islands/index.html
• Zee, G. (2017, September 06). How hurricanes form, explained by ABC News chief meteorologist Ginger Zee. Retrieved October 09, 2017, from http://abcnews.go.com/US/hurricanes-form-explained-abc-news-chief-meteorologist-ginger/story?id=49650211

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