Last week Hurricane Sally caused havoc along the US Gulf Coast. In what’s turning out to be an exceptional hurricane season (looking set to rival 2005’s record-breaking 28 named Atlantic storms), it turns out that Sally’s last minute ferocity may have been fuelled by Hurricane Marco three weeks previously.
Back in October 2018 Hurricane Michael became the strongest storm on record to make landfall on the Florida Panhandle. This category 5 hurricane took everyone by surprise: intensifying rapidly and resulting in 16 fatalities and $25bn in damage. Brian Dzwonkowski, from the University of South Alabama, and colleagues, analysed the conditions that preceded Michael and found that the scene was set five weeks earlier, when tropical storm Gordon powered through, churning the water on the tropical shelf and removing the cool bottom layer.
Their research, published in Nature Communications, shows that warm weather then reheated the upper ocean, creating the fuel to intensify Michael. And without the cool bottom layer there was nothing to slow Michael down.
Coupled hurricanes and heatwaves like these are likely to become more frequent in a warming world, but understanding how they interact will help forecasters to improve predictions of storm intensity and decide when evacuation is necessary.
