Hurricanes (DP IB Geography)

Revision Note

Distribution of Hurricanes

  • “Hurricane” is one of the names given to tropical storms:

    • Other names used for tropical storms include cyclones and typhoons

    • Storm names vary depending on the location in which they form

  • Hurricanes form over waters in tropical or subtropical regions:

    • Hurricanes usually form in the Atlantic Ocean, the middle or northeast of the Pacific Ocean, the Caribbean Sea and the Gulf of Mexico

    • Hurricanes form in these regions as the waters are warmer

  • Hurricanes tend to occur over the months of June – November

  • The Pacific Ocean has the largest number of hurricanes per year

  • More hurricanes occur in the northern hemisphere than in the southern hemisphere

Examiner Tips and Tricks

Make sure you are aware of how climate change could impact the intensity of hurricanes. What happens if waters further from the equator start to get warmer? 

Distribution of tropical storms

World map showing regions where tropical storms occur. Hurricanes in the Atlantic and Northeast Pacific, cyclones in the Indian Ocean, and typhoons in the Northwest Pacific.
Distribution of tropical storms

Formation of Hurricanes

  • Hurricanes are low-air-pressure systems formed over oceans

  • Hurricanes need warmer waters to form (minimum 27 degrees Celcius)

  • Warm and moist air above the ocean rises upwards, leaving behind a pocket of low pressure underneath

  • Cooler air moves into this low-pressure area, heats up and rises

  • This air cools and condenses as it rises and releases heat energy, forming clouds and storms

  • The Coriolis Effect causes a spinning action. Storms in a low-pressure system will spin clockwise in the southern hemisphere and anti-clockwise in the northern hemisphere

  • As this process intensifies with more heat energy, winds will increase and the spinning will worsen

  • Wind with low wind shear helps storm clouds rise straight upwards

  • The centre of a hurricane is the eye:

    • This is a large area of low-pressure air that is colder and drier

    • It results in a calm centre inside the storm

  • When hurricanes reach land or move over colder waters, they will lose energy and slow down

  • The Saffir-Simpson scale shows the intensity of hurricanes, by measuring wind speed 

Formation of a hurricane

Diagram explaining tropical storm formation: ocean temperature above 27°C, warm air rises, storm surge at center, winds increase at eyewall, clear eye, and dense cloud canopy.
Formation of a hurricane

Examiner Tips and Tricks

Remember, hurricanes need a perfect balance of several conditions to form. Just because the water is warm, doesn’t mean a hurricane will develop. It requires a combination of different factors.

Impact of Hurricanes

  • Hurricane paths are hard to predict. This makes it more difficult to prepare for and manage hurricanes

  • Hurricane winds can rip up trees, cause airborne debris and damage infrastructure, e.g. homes, power lines etc.

  • Hurricanes can cause a rise in the water level, resulting in storm surges. This can cause dramatic coastal flooding as the wind moves the water inland

  • Flooding can occur inland as a result of heavy rainfall after the hurricane

  • Hurricanes can affect boats and offshore oil/gas stations out on the ocean

Case Study: Hurricane Katrina

Case Study – Hurricane Katrina

  • Hurricane Katrina was a category 5 hurricane that hit the Gulf Coast in 2005

  • It formed over the Atlantic Ocean, building up to be one of the most deadly hurricanes in history

  • It battered the areas of Florida, Mississippi and Louisiana, among others

The path of Hurricane Katrina as it hit the southwest coast of the US

Map showing a hurricane path originating in Miami and passing through the Gulf of Mexico, hitting New Orleans and ending near Huntsville. Path markers indicate storm intensity.
The path of Hurricane Katrina as it hit the southwest coast of the US

Impacts of Hurricane Katrina

  • Roughly 1833 people died with millions of people left homeless

  • Damages cost roughly $300 billion 

  • New Orleans was the worst hit area:

    • Storm surges caused intense flooding

    • Levees and floodwalls were not strong enough to deal with the Category 5 storm

    • This failure of flooding protection resulted in the dramatic loss of life

  • Coastal erosion destroyed beaches

  • Land and forests were destroyed, impacting habitats and ecosystems

  • Residents were left stranded, causing tensions. This resulted in increased crime e.g. looting

  • People did not have any electricity for up to a week

  • Tourism was severely affected

  • The hurricane affected the agriculture and oil/gas industry, negatively affecting the economy

Responses to Hurricane Katrina

  • Evacuation during Hurricane Katrina was poorly planned:

    • Many underprivileged people were left stranded

  • The US government provided $50 billion, whilst other countries sent aid relief 

  • The Superdome (stadium) became a space for people to find shelter and food:

    • There were issues with food availability and unsanitary conditions 

  • Eventually, repairs were made to the levees and floodwalls, however, it took many months until the water was gone

  • Many people living back in New Orleans cannot get home insurance or have to pay very high premiums as a result of hurricane risk

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