Another one? Hurricane Milton, which is barrelling towards Florida鈥檚 west coast, is the fifth hurricane to form over the Atlantic in the past two weeks, arriving on the heels of devastating floods brought by Hurricane Helene. This surge of activity feels all the more surprising given it follows an extended lull that had forecasters scratching their heads. But with warmer oceans due mainly to climate change, researchers say this was bound to happen.
鈥淭he ceiling was high right at the start of the season and I think this burst is a realisation of that potential,鈥� says at the University at Albany in New York. 鈥淲e knew that [lull] wasn鈥檛 going to last.鈥�
Hurricanes have kept forecasters guessing this year. Predictions in May saw talk of an 鈥�extraordinary鈥� Atlantic hurricane season. The US National Oceanic and Atmospheric Administration (NOAA) projected 17 to 25 named storms, its largest forecast ever. Another group forecast as many as 39 named storms, far above the record 30 seen in 2020. This bullishness was mainly down to two factors: the above-average heat in the North Atlantic would fuel developing storms, while a shift towards a cooler La Ni帽a pattern in the Pacific Ocean would cut down on the winds that tear them apart.
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Those projections looked solid when Hurricane Beryl developed at the start of July, becoming the earliest category 5 storm to form on record. But things then went 鈥渧ery quiet鈥�, says at Colorado State University. That prompted rounds of speculation about what was suppressing the storms, with ideas ranging from a delayed transition to La Ni帽a possibly linked to anomalous cooling in part of the Atlantic, to dusty wind from the Sahara desert drying the air.
Whatever the cause, that lull is over. 鈥淎s soon as we got activity going in the Gulf, it exploded,鈥� says at Climate Central, a US-based non-profit research organisation. This shift may be related to a change in a larger-scale pattern of winds called the Madden-Julian oscillation that reduces wind shear; another possibility is that hurricanes that usually form farther west during this part of the season are outside the influence of Saharan dust, says at the Pacific Northwest National Laboratory in Washington. Either way, with Helene forming on 24 September, the ocean appears to have awoken.
This storm rapidly intensified and made landfall on the Gulf coast of Florida three days later as a category 4 hurricane. Fast winds and its sheer size sustained torrential rain as far inland as Ohio, resulting in flooding that killed more than 200 people across the south-east US and caused damage probably running into billions of dollars. Rapid attribution studies have found warmer temperatures due to climate change boosted the rainfall by as much as 50 per cent in some inland areas, and made the high sea surface temperatures that fuelled the storm hundreds of times more likely. In a painful irony, one of the US鈥檚 mostin Asheville, North Carolina, remains out of operation due to the floods.
But even as the damage and drivers of Helene are still being assessed, the start of October has brought four more hurricanes, including three 鈥� Kirk, Leslie and Milton 鈥� spinning at the same time 鈥� another first this late in the Atlantic season. While Kirk and Leslie formed far out in the ocean to the east, Milton took shape within the Gulf of Mexico. In under 24 hours 鈥� also due to 鈥� it had strengthened at near-record speed to a category 5 storm with sustained wind speeds of 290 kilometres per hour (180 miles per hour), and one of the lowest barometric pressures on record 鈥� which Tang says is a more reliable measure of potential damage than wind.
Milton briefly weakened due to wind shear from a separate weather system entering the Gulf as well as a process in which the slower-moving outer eyewall of a hurricane replaces the inner eyewall 鈥渓ike a snake shedding its skin鈥�, says Tang. But on 8 October it regained strength as a Category 5 before weakening once more to Category 4. While this means slower winds, Tang says it could make the storm larger, enhancing storm surge. It is now to make landfall near Tampa Bay, Florida, later this evening as an 鈥渆xtremely dangerous major hurricane鈥�, , bringing intense winds and a storm surge around the state. 鈥淭here鈥檚 going to be water in areas that have not seen water in recent memory,鈥� says Tang.
