A hard rain’s a-gonna fall

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  • Greater threat: we are experiencing storms with stronger wind speeds and higher amounts of rainfall than was once the norm

    Greater threat: we are experiencing storms with stronger wind speeds and higher amounts of rainfall than was once the norm

The Atlantic hurricane season is a humbling annual reminder that nature remains wild, unpredictable and highly dangerous despite any pretensions we may have about taming the world around us.

And certainly the uncontrolled fits of insanity the natural world has succumbed to thus far during the 2017 season should leave no doubt in any Bermuda resident’s mind that only a combination of luck and the volatility of tropical storm paths has spared us the type of near-apocalyptic destruction experienced in the Caribbean and huge swaths of Texas.

Whether that good fortune holds out until the end of the season, November 30, remains to be seen.

Bermuda’s settlement came about as a result of a hurricane and the island will be forever linked with these great cyclonic storms in the public’s imagination, thanks to Shakespeare’s Tempest, which memorialised and mythified the 1609 wreck of the Sea Venture here.

But the reality is that Bermuda is such a small target in such a vast ocean that hurricanes have only rarely made landfall here. On average we have experienced a direct hit or a close-enough call to cause destructive damage on the island only once every six or seven years.

But since 2014, of course, there have been three dead-on strikes: Fay and Gonzalo, which ploughed ashore within a week of one another in 2014, and the Category 4 monster Nicole, which churned across Bermuda last October.

It’s not just the growing frequency of hurricanes in the Bermuda area that has raised the eyebrows of veteran shark-oil watchers; it’s that these storms have been increasing in strength as well in recent decades.

Whether you rely on one of Bermuda’s redoubtable shark liver-oil barometers or the latest in satellite technology to gauge a hurricane’s power, professional and amateur storm watchers alike are arriving at a common conclusion. Namely, that we are experiencing storms with stronger wind speeds and higher amounts of rainfall than was once the norm, and these storms are only likely to grow more destructive, last longer and make landfall more frequently than was the case in the past.

This phenomenon holds true of the entire Atlantic basin and is strongly associated with warmer-than-usual sea surface temperatures. This is the fuel that supercharges hurricanes and can transform a high-end tropical storm into a Category 5 behemoth literally overnight, as we witnessed this week with the terrifyingly rapid intensification of Maria.

The science involved is straightforward enough.

As tropical storms move across the open sea, they pick up energy from the warm ocean surface and become more powerful.

Simply put, the more heat near the ocean’s surface, the more potential exists for strong winds and heavy rains to be created.

With global temperatures on the rise, whether owing to natural processes or man-made factors, or a combination of both, more heat is being absorbed by the oceans than ever before, providing a ridiculously abundant energy source for hurricanes.

For instance, as Hurricane Harvey barrelled towards Houston last month, sea-surface temperatures off the Texas coast were between 2.7F and 7.2F higher than is usually the case at that time of year.

As a result, Harvey grew from a tropical depression to a Category 4 hurricane in less than 48 hours — and then kept intensifying even as it made landfall, an unprecedented and, frankly, ominous occurrence, according to meteorologists.

In the past 30 years, not a single hurricane west of Florida has intensified in the last 12 hours before sweeping ashore because, as they feed off and churn the warm waters near the ocean surface, cooler waters naturally rise that serve to dissipate energy and blunt the storms’ impact.

Harvey was churning up water between 300 and 600 feet deep as it bore down on Texas — but even at those depths, it was still unusually warm. And so the hurricane continued to grow and strengthen as it hit the Lone Star State, dumping devastating amounts of rainfall on to some areas, forcing the evacuation of more than 30,000 people and causing catastrophic damage estimated to run into tens of billions of dollars.

“Harvey was not in a good position to intensify the way it did because it was so close to land,” Kevin Trenberth, a senior scientist at the US National Centre for Atmospheric Research, recently told The Atlantic. “It’s amazing it was able to do that.”

Amazing but likely not unique. For Harvey probably isn’t a statistical anomaly, a one-off freak. Rather this highly abnormal storm may be representative of a worrying new norm in terms of Atlantic storms as sea temperatures continue to grow warmer.

“This is the main fuel for the storm,” Trenberth said. “Although these storms occur naturally, the storm is apt to be more intense, maybe a bit bigger, longer-lasting and with much heavier rainfalls [because of that ocean heat].”

The 2017 hurricane season is already one for the record books for any number of unhappy reasons. This month Hurricane Irma became the first Category 5 hurricane known to strike the northern Leeward Islands, equalling the intensity of the strongest hurricane ever to make landfall in the western hemisphere — the 1935 Labour Day hurricane that devastated parts of Florida.

This season is also the first on record to feature two Atlantic hurricanes making landfall in the United States at Category 4 intensity or stronger. It is also the first season since 2010 to feature four Category 4 hurricanes in the Atlantic, and one of only six years on record to feature at least two potentially catastrophic Category 5 hurricanes.

With sea surface temperatures remaining unseasonably warm well into the autumn, offering an ideal energy source for late-season hurricanes, there is more than ample time for further records to be set.

With two more months of hurricane season to go, Bermuda residents are well advised to keep their eyes peeled on the weather forecast or their shark-oil barometer because chances are things are only going to grow wilder, more unpredictable and increasingly dangerous.

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Published Sep 21, 2017 at 8:00 am (Updated Sep 21, 2017 at 7:41 am)

A hard rain’s a-gonna fall

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