ARE WE GETTING MORE HURRICANES?

Dr Dann Mitchell, climate scientist at the University of Bristol

In the Atlantic basin, the hurricane season normally lasts from June to November, peaking in September. The fact that we’ve seen eight hurricanes so far this year [as of 25 September] is markedly out of the ordinary – the average per season is six. However, perhaps more profound is the sheer number of strong hurricanes: this year was the first time in recorded US history that three Category 4+ hurricanes had made landfall in a single season. But whatever the remainder of the season brings, it’s unlikely to be as active as the famous 2005 season. This saw Katrina, one of 15 hurricanes that year, devastate the US coastline and left much of New Orleans underwater.

Is there a link with climate change?

We know that a warmer atmosphere can hold more rain than a cooler atmosphere, so the downpour over Texas during Hurricane Harvey may have been worsened by climate change. We also know that hurricanes get their energy from the heat in oceans, so warmer oceans are theorised to lead to stronger hurricanes, although not necessarily to a change in the number of storms. But it’s too early to say for sure whether the strong hurricanes we’ve been seeing recently are a result of climate change. To know this, we need to see a trend over a longer period, so time will tell. We’re more sure, however, that climate change will worsen the impact of any storm surges caused by a hurricane’s strong winds. With sea levels rising, storm surges can make it further inland, potentially leading to more widespread flooding.

Are we getting better at predicting hurricanes?

The hurricane path is perhaps the most important part of a forecast because you need to prepare when a hurricane’s on its way. This is especially true if the system is travelling over low- lying islands, where storm surges can be devastating. Due to these risks, the US has invested heavily in predictive research, and now a reasonable forecast of a hurricane’s path can be made three to five days ahead of time. A day before the hurricane hits, we can forecast its centre to within about 64km (40 miles). It was remarkable how close to the forecast Hurricane Irma came, and this undoubtedly saved lives.