The catastrophic consequences of intense tropical cyclones are no news. Torrential rains, deadly flooding, winds of immense destructive power, and storm surges that can wipe out coastal areas have all made headlines. However, a recent study from the University of Hawai‘i at Mānoa has unveiled a worrying trend. As the climate warms, devastating hurricanes and cyclones aren’t just becoming more frequent or powerful – they’re coming earlier.
The study was spearheaded by Pao-Shin Chu, an atmospheric sciences professor at the UH Mānoa School of Ocean and Earth Science and Technology and the Hawai‘i State Climatologist.
His research reveals that since the 1980s, Category 4 and 5 hurricanes (those with wind speeds greater than 131 miles per hour) are making their presence felt three to four days earlier with each passing decade. Such a shift in the seasonal cycle means these severe storms are arriving not in their expected period, but much earlier, causing unforeseen challenges for affected communities.
Chu remarked, “When intense tropical cyclones occur earlier than usual, they disrupt the preparedness measures of communities. This unexpected arrival can coincide with other weather systems, such as local thunderstorms or seasonal monsoon rainfall, creating compounded extreme events. The result? An overwhelmed emergency response.”
While the characteristics of intense hurricanes in a warming climate, like their number, intensity, and lifespan, are already a matter of significant research, the shift in their seasonal timing was a less-explored area – until now.
To gain insights into these changes, Chu and his team delved deep into a variety of data sources. Using satellite imagery, historical cyclone tracks, rainfall records from NOAA, and an array of statistical methods, the researchers discerned a significant repositioning of these intense cyclones from autumn months to summer since the 1980s.
This trend was especially pronounced in regions like the eastern North Pacific off Mexico’s coast (the source of most hurricanes impacting Hawai‘i), the western North Pacific, the South Pacific, the Gulf of Mexico, and the Atlantic coast of Florida and the Caribbean.
The consistency of earlier hurricane arrivals, as revealed by both satellite data and traditional ground observations, took Chu by surprise. Citing an example, he mentioned Hurricane Harvey, which in August 2017, as a Category 4 storm, slammed into Texas and Louisiana, resulting in catastrophic flooding and claiming over 100 lives.
Probing further, the research team used various global climate model simulations, like the high-resolution CMIP6 models. They found that warmer oceanic conditions, which are conducive to the genesis of intense tropical cyclones, were developing earlier, mainly due to greenhouse gas forcing.
“In a world where carbon dioxide levels continue to rise unchecked, this trend of earlier cyclone arrivals will only intensify,” warned Chu.
Areas like South China and the Gulf of Mexico are already witnessing the repercussions, as the early advent of these cyclones is triggering extreme rainfall ahead of its usual time.
The implications of these findings are far-reaching. With tropical cyclones appearing earlier than expected, there’s a heightened risk of their simultaneous occurrence with other severe weather events.
Chu emphasized the gravity of this situation, stating, “Given this advancing timeline of intense cyclones, the potential for their confluence with other high-impact weather phenomena should ring alarm bells. It’s crucial to understand the shifts in hurricane activity due to global warming, as this knowledge is pivotal for disaster prevention, managing resources, and ensuring community readiness.”
This study underscores the importance of adaptive measures and enhanced preparedness as we grapple with the unpredictable twists and turns of a rapidly changing climate.
Their findings were published recently in Nature.
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