Hurricane Intensity

Featured image taken by NASA astronaut Jack Fischer aboard the International Space Station.

Hurricanes: Powerful Tropical Storms

Hurricanes are one of the most destructive forces on Earth. The term “hurricane” comes from Hunraken or Huracán, the name of the god of winds and destruction of the native Mayan and Caribbean people. Hurricane is a regional term for a tropical cyclone that forms in the Atlantic, eastern North Pacific, or eastern South Pacific Ocean. Tropical cyclones are a low-pressure weather system with rotating winds. Tropical cyclones with winds less than 39 mph are known as tropical depressions. Tropical storms have winds between 39 and 74 mph; when a tropical storm achieves wind speeds of 74 mph, it becomes a hurricane.

Hurricane formation is driven by heat. During hurricane season, which falls between June 1 and Nov 30 each year, hot air from over the African continent warms ocean waters, causing evaporation. This warm, moist air rises, creating an area of low pressure. Surrounding air flows toward the low-pressure area to replace the rising air, before warming and rising itself. As air travels over the rotating surface of Earth, it is deflected and begins to rotate, High in the atmosphere where it is much cooler, water vapor condenses and forms clouds, and the system continues to grow and strengthen. Eventually the characteristic ‘eye’, is formed. This is an area of generally clear and calm weather at the center of the storm roughly 20-40 miles across. Hurricanes can be up to 11 miles high; there are, on average, 12 hurricanes a year that form in the tropical Atlantic Ocean.

Diagram of hurricane formation, structure, location and movements, and major United States hurricanes. (image from: http://www.relativelyinteresting.com/hurricanes-explained-how-they-form-and-their-anatomy/ (Original Source: NOAA, USGS, Infographic World/Popular Science)

Thank you for listening; this has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Contributing Professor: Dr. Henry Potter

Script Author: James M. Fiorendino

Could Future Hurricanes Be More Intense?

Hurricanes are already one of the most destructive natural forces on the planet, but could they be worse in the future? Tropical storms like hurricanes require heat energy to grow and sustain themselves; severe hurricanes might occur more frequently due to greater availability of heat energy.

The Saffir-Simpsons Hurricane Wind Scale. Image from: https://www.vox.com/science-and-health/2016/10/6/13191010/how-hurricanes-form-tropical-storms-guide

Currently, hurricanes are classified according to the Saffir-Simpson hurricane wind scale, which ranges from 1 to 5. A category 1 storm is characterized by winds between 74 and 95 mph, which may cause limited damage to homes, such as blowing shingles off roofs, or snapping tree limbs. In comparison, a category 5 storm has winds of 157 mph or greater, and is capable of destroying homes and blowing over trees, causing massive power outages.

An early map predicting of the movement of Hurricane Harvey when it was still a tropical storm moving over the Windward Islands. The solid cone denotes 1-3 day position predictions, while the dotted cone shows predictions for the storm's position after 4-5 days. — An early map predicting of the movement of Hurricane Harvey when it was still a tropical storm moving over the Windward Islands. The solid cone denotes 1-3 day position predictions, while the dotted cone shows predictions for the storm’s position after 4-5 days.

Predicting hurricane strength, or where a hurricane will make landfall, is essential for effective preparations and evacuations. Several factors impact hurricane formation and movement. Generally, hurricanes travel east to west, following trade winds along the equator; areas of high and low pressure in the atmosphere guide the storm, like hills and valleys guide a river. Hurricanes require warm air and ocean water to form, yet as they move they stir up the ocean, bringing cold water to the surface, reducing the energy available to them. Scientists are working to better understand hurricanes and improve models forecasting hurricane strength and movement.

Contributing Professor: Dr. Henry Potter

Script Author: James M. Fiorendino

Studying Hurricanes

Understanding how hurricanes form and move is essentially for accurate forecasting of storms, allowing effective preparations and evacuations to be made. But how do you study something so massive and powerful? Scientists rely heavily on satellites to gather data on hurricanes. Heat acts as fuel for hurricanes; satellites orbiting the Earth gather important data about the temperature of the oceans and atmosphere. Additionally, satellites measure sea surface height. Water expands and contracts as it warms and cools; consequently, warmer areas of the ocean will be higher than colder areas. Measuring sea surface height helps scientists determine how much heat is stored in the ocean that may contribute to hurricane intensity.

The above image from NASA's website visualizes sea surface height data from the SARAL and Jason-2 missions. Image from: https://sealevel.jpl.nasa.gov/images/latestdata/ssh/2018/SSHA_20180404_010000.png — The above image from NASA’s website visualizes sea surface height data from the SARAL and Jason-2 missions. Image from: https://sealevel.jpl.nasa.gov/images/latestdata/ssh/2018/SSHA_20180404_010000.png

Unfortunately, temperature data collected by satellites is limited to surface waters. Hurricanes mix the ocean as they move, bringing deep water to the surface. While satellites can tell how much heat is stored in the ocean, satellite data do not describe To supplement satellite data, scientists observe the ocean directly using buoys, autonomous vehicles, and research vessels. By combining data from these various instruments, scientists are able to gain a more complete description of how much and where heat is stored in the ocean before and after a hurricane.

A Slocum glider ready for deployment. Gliders fly through the water by altering their buoyancy, causing them to sink or float. Their wings help to propel them forward.

This image shows a visualization of temperature data collected by one of TAMU's gliders in the Gulf of Mexico. Image from: http://gcoos2.tamu.edu/gandalf_data/deployments/tamu/unit_540/plots/ — This image shows a visualization of temperature data collected by one of TAMU’s gliders in the Gulf of Mexico. Image from: http://gcoos2.tamu.edu/gandalf_data/deployments/tamu/unit_540/plots/

Contributing Professor: Dr. Henry Potter

Script Author: James M. Fiorendino

Hurricane Harvey

Hurricane Harvey struck the coast of Texas on August 25, 2017, becoming the costliest hurricane in United States history, having caused nearly $200 billion in damage. Most of the damage from Harvey was due to flooding; 33 trillion gallons of water fell in total, with some areas of Houston reporting as much as 60 inches of rain. What was unique about Harvey was the speed with which it developed into a severe hurricane. On August 22, Harvey passed over the Yucatan Peninsula as a weak tropical storm before moving into the Gulf of Mexico. While traveling over the warm waters of the gulf, Harvey intensified from a tropical storm to a category 4 hurricane in just 40 hours before striking Texas, an unexpectedly rapid increase in strength.

Currently, scientists at Texas A&M University’s department of oceanography are studying the factors that contributed to hurricane Harvey’s intensification as well as the effects of the storm. Luckily, oceanographers from Texas A&M University conducted a research cruise in the Gulf of Mexico shortly before Harvey struck Texas. After hurricane Harvey, a team of scientists convened for the Harvey Rapid Response cruise to investigate the impacts of the storm, collecting physical, chemical, and biological data to determine how Harvey affected the Gulf of Mexico, particularly regarding the massive influx of fresh water. These data may also offer insight into why Harvey intensified so rapidly.

A suite of oceanographic instrument known is lowered through the water column from the RV Point Sur during the Hurricane Harvey Rapid Response Cruise. Image credit: James M. Fiorendino — A suite of oceanographic instruments is lowered through the water column from the RV Point Sur during the Hurricane Harvey Rapid Response Cruise. Image credit: James M. Fiorendino

Chief Scientist Dr. Steve DiMarco and TAMU students carefully wrangle a cage containing several oceanographic instruments back onto the deck of the RV Point Sur during the Hurricane Harvey Rapid Response Cruise. Photo Credit: James M. Fiorendino

Contributing Professor: Dr. Henry Potter

Script Author: James M. Fiorendino