How and Why Do Hurricanes Occur?

Hurricanes (also known as tropical cyclones) develop over the Atlantic or eastern Pacific oceans. Hurricanes gather the warm, moist air around the equator and begin to develop in that area first before the trade winds take the hurricanes to land. (Doyle, 2018). The westward blowing wind over the Atlantic Ocean from Africa gives the wind that is necessary to develop this tropical cyclone. (NOAA, 2013). Since the hurricanes takes all the air warm air from the surface this makes an area of lower air pressure on the surface which hints at bad weather incoming. Typically, hurricanes will weaken once they make landfall since they lost all the energy coming from the warm water at sea (Doyle, 2018).

There are key ingredients that are necessary to create a hurricane which include an existing weather disturbance like a tropical wave, warm water, thunderstorm activity and a small difference in wind speed as well or direction. The amount of energy that is created from a hurricane is almost equivalent to almost half the electrical generating capacity of the whole world. The warm water from the ocean and thunderstorms are a main source of energy for the hurricanes to get stronger and bigger. The eye of the hurricane is relatively calm while the areas surrounding the eye called the eyewall is where the harshest weather and winds will resides (NOAA, 2013).

The formation of the eye is important to understanding how hurricanes occur as well. The convection just below the tropopause needs to preserve its tangential momentum. Vortex tilting and gravity wave multiplication create subsidence which creates the eye wall. When a band of convection closes off a section, the subsidence rate increases which causes more intensification of the system. Thus, the eyewall is where the harshest weather conditions can be found and what is left in the center is the eye, the calmest part of the system. W.M. Gray made an observation that hurricanes develop in two stages. The first stage has a brief wind surge that creates a cloud cluster where there is a high rate of warming and spin-up rate. The second stage of storm development to a named hurricane would require an even larger wind surge to create a significant pressure drop (Pearce, 2005).

Meteorologist have derived four stages of hurricane development which include: tropical disturbance, tropical depression, tropical storm and tropical cyclone.

A tropical disturbance occurs when the warm ocean water condenses to form clouds that emit heat into the atmosphere. This warm air will rise and develop into columns of clouds which will eventually get larger and bigger due to evaporation and condensation. Once it gets big enough, this collection of columns will develop into a thunderstorm clouds (Stoller-Conrad, 2019).

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At the top of the cloud column, the air will cool and become unstable which is releasing heat from cooling water vapor thus making the top clouds warmer and pressure higher. These winds will diverge from the high pressure and causes the surface pressure to lower. Air from the surface will move to the low pressure area and create more thunderstorms and this will make wind speeds pick up to 25-38 mph classifying it as a tropical depression (Stoller-Conrad, 2019).

Once wind speeds hit 39 mph it is categorized as a tropical storm and the wind direction depends on the hemisphere that the storm is in. The storm will spin counterclockwise in the northern hemisphere and clockwise in the southern hemisphere because of the Coriolis force (Stoller-Conrad, 2019).

After 74 mph, the tropical storm is now a tropical cyclone or the common term, hurricane. The storm will be at least 50,000 feet in the sky and approximately 125 miles in diameter. The trade winds will push the hurricane westward to the Caribbean, the Gulf of Mexico or the southeastern coast of the U.S (Stoller-Conrad, 2019).

To put things into context of a recent storm that hit the U.S., I will be using Hurricane Michael as an example. Hurricane Michael started off as a weak, disorganized tropical system in the Southwestern Caribbean but was not in optimal conditions to further develop the storm. Even with the subpar conditions, convection occurred with the tropical disturbance causing the storm to accumulate together. The system produced heavy rainfall and strong winds in central America and soon the National Hurricane Center announced the first advisory about the system at 5:00 pm EDT on October 6th, 2018. Even though the disturbance was sitting around 23 to 35 mph wind shears, it would soon be classified as a tropical depression by 5:00 am EDT on October 7th, 2018 due to potential conditions. Said conditions, such as low-level circulation concentrating and max winds reaching 40 mph, seemed to be promising for even further development of the system to become a tropical storm within 8 hours of tropical depression status. Finally, on October 8th, 2018 at 11 am EDT, a hurricane watch was in effect as the system was declared a category 1 hurricane. The conditions seemed to only foster the growth of the storm with abnormally warm sea level temperatures, lowering environmental shear and increasingly ample moisture. Hurricane Michael quickly had the potential to become a very large and powerful storm eventually making landfall on the Florida Panhandle around 1:30 pm EDT on October 10th, 2018 as a category 4 hurricane (US Department of Commerce, 2018).

Works Cited

• Doyle, Heather. “How Do Hurricanes Form?” NASA, NASA, 11 Apr. 2018, https://spaceplace.nasa.gov/hurricanes/en/.
  • This source provided a simple overview of how hurricanes are formed.
• US Department of Commerce, and National Oceanic and Atmospheric Administration. “How Do Hurricanes Form?” NOAA’s National Ocean Service, 28 June 2013, https://oceanservice.noaa.gov/facts/how-hurricanes-form.html.
  • This source provided a basic and concise description of how hurricanes form with an explanation about the eye of the storm as well.

• Stoller-Conrad, Jessica. “How Does a Hurricane Form?” How Does a Hurricane Form? | NOAA SciJinks – All About Weather, SciJinks, 5 Apr. 2019, https://scijinks.gov/hurricane/.
  • This source provided an in-depth overview of the development stages of a hurricane.
• Pearce, Robert. “Why must hurricanes have eyes?.” Weather 60.1 (2005): 19-24.
  • This article talks about hurricane formation but especially the eye of the storm which is
  • an important component of the hurricane.

• US Department of Commerce. “Hurricane Michael 2018.” National Weather Service, NOAA’s National Weather Service, 23 Apr. 2019, www.weather.gov/tae/HurricaneMichael2018.
  • This source provided insights about the findings of how Hurricane Michael started and its impact on the US.