Some tropical storms rapidly transform into a category five hurricane. Cutting-edge saildrones are helping to reveal how this process happens.
Hurricane Otis made landfall on the coast of southern Mexico on 25 October 2023 as a category five hurricane, battering towns and cities in its path with 165mph (270km/h) winds. At least 27 people were killed by Hurricane Otis, which caused widespread damage to buildings and power outages in Acapulco, a large port city and popular tourist destination, in the state of Guerrero.
The US National Oceanic and Atmospheric Administration (NOAA) described Otis as a “life-threatening storm surge” which would bring large and dangerous waves, destructive winds and heavy rainfall. This could lead to flash flooding and mudslides, NOAA warned.
“There are no hurricanes on record even close to this intensity for this part of Mexico,” according to the National Hurricane Center.
Hurricane Beryl
On Friday 28 June 2024, Hurricane Beryl rapidly intensified from a tropical storm into a category four hurricane, moving towards the Windward Islands of the western Caribbean. The storm is expected to make landfall on Barbados on 1 July, with life-threatening winds and storm surge.
Beryl became the first hurricane of the Atlantic hurricane season, and the second named storm after Tropical Storm Alberto.
The 2024 Atlantic hurricane season is expected to be extremely active, with four to seven major hurricanes expected, compared with an average of three.
Forecasters said Otis “explosively intensified” by 110mph (177km/h) within 24 hours, rapidly morphing from a tropical storm into a category five hurricane. More storms like this are on the horizon as climate change causes hurricanes to intensify. The proportion of hurricanes that become category four and five is projected to increase due to climate change. Rising ocean temperatures are making storms transform rapidly into powerful hurricanes in a single day, according to a 2022 study by researchers at the University of Reading in the UK.
Now scientists are hoping to find out more about what leads these destructive storms to grow in intensity over such a short period of time.
NOAA has partnered with US company Saildrone, a data company that manufactures seafaring drones, to deploy instruments capable of weathering the high winds and waves of developing hurricanes. These saildrones are packed with sensors to collect data about the oceanic and atmospheric conditions, which is then relayed to the government agency whose scientists will analyse the data.
A saildrone is a “wind-propelled vehicle that looks a lot like a sailboat”, says Julia Paxton, director of mission management at Saildrone. The drones – which come in a variety of sizes, either 23ft (7m), 33ft (10m) or 65ft (20m) long – combine wind propulsion with solar-powered meteorological and oceanographic sensors that allow scientists to measure the track, or path, a hurricane it taking along with changes in its intensity over time.
The saildrones can also capture data beneath the waves and analyse ocean currents. This helps “create a complete [picture] of the air and water column, from 30,000ft (9,144m) above [sea level] to several 1,000ft (300m) below the surface”, says Paxton.
Saildrone’s mission is “not about predicting hurricanes this season”, says Paxton. “It’s about studying why and how hurricanes intensify so that in the future we can improve hurricane modelling.”
Hurricanes form over warm water surfaces. As the ocean water evaporates and rises as warm air, it forms an area of low pressure underneath. This results in more air rushing in, which rises and cools and forms clouds and thunderstorms, which in turn release water droplets. This leads to the evaporation of even more water, fueling the storm. When wind speeds reach 74mph (119km/h) within such a storm, it is classified as a hurricane.
“The energy source for a hurricane is the transfer of heat from the ocean to the atmosphere,” says Kerry Emanuel, professor emeritus in atmospheric science at the Massachusetts Institute of Technology (MIT).
“Before this project, there weren’t any platforms that could measure the exchange of heat and momentum between the ocean and hurricanes, which could be steered into the path of a hurricane,” says Greg Foltz, a NOAA scientist and one of the principal investigators of the mission.
Source: BBC
