Three main factors come together to intensify a hurricane. The first is that as the world as a whole warms, so do our oceans. Water that evaporates from the earth’s surface rises and releases heat that fuels the forming hurricane. The warmer some of the ocean water is, the more energy the cyclone has to harness. When a hurricane like Lee forms off the coast of Africa, it feeds a lot of food into the Atlantic Ocean as it makes its way toward the U.S. East Coast. As this year’s hurricane season approaches, temperatures in the tropical Atlantic Ocean remain extremely high.
The second factor is humidity. As the atmosphere warms, it can hold more water vapor, making some parts of the world more humid. Hurricanes like this because dry air causes cooling, which can create downdrafts that counteract the updrafts that cause storms. “As long as conditions remain wet, the storm could intensify or maintain its strength,” Balaguru said. “But once the core enters a dry environment or becomes less humid, the storm begins to weaken.”
And finally, hurricanes dislike wind shear, or winds that have different speeds and directions at different altitudes. (Think of it like layers of a cake made only of air.) Instead, cyclones prefer a stable atmosphere, where the winds can swirl and strengthen. Wind shear can also inject dry air from outside the storm into the center of the hurricane, further weakening it. As the world warms, wind shear is decreasing along the U.S. East Coast, East Asia, and South Asia. Provides an ideal atmospheric environment Because cyclones occur and intensify. “Due to climate change, the upper troposphere is expected to warm faster than the surface,” Balagul said. “This increases atmospheric stability and may also weaken the tropical circulation.”
In the short term, La Niña conditions in the Pacific Ocean could lead to more hurricane formation and intensification this summer. Although La Niña is in a different ocean area, it tends to suppress Atlantic winds, so there is less wind shear, which hurricanes dislike. Therefore, the University of Arizona predicted that a very active hurricane season, coupled with very high sea surface temperatures in the Atlantic Ocean, would promote storms. In contrast, last year’s El Niño created wind conditions in the Atlantic Ocean that prevented cyclones from forming.
Still, Hurricane Lee developed into a superstorm last September. A week earlier, Hurricane Idalia rapidly strengthened just before hitting Florida. This type of intensification near the coast is extremely dangerous. “When a storm is very close to the coast, for example, it lasts a day or two, and then suddenly intensifies quickly, it can catch us off guard in terms of preparedness,” Balaguru said. A town may have made evacuation plans based on winds of 160 mph, but suddenly the winds were closer to 130 mph.
Unfortunately, Balaguru’s new study finds that climatic conditions, especially near coasts, make storms more likely to intensify. It’s up to Zeng and his team at the University of Arizona to further refine their predictions to manage the growing risks to coastal populations. “For scientists, seasonal predictions are a reality check on our understanding,” Zeng says. “We’ve done pretty well the last few years, so that gives us even more confidence going forward.”
