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Irma's size, intensity pushed by rising temps

Associate editor — Features

Wednesday, September 13, 2017

Spanning over 220,000 square miles, and lasting 14 days, almost four of which were spent at Category five, Hurricane Irma is the biggest storm ever recorded, and while climate scientists aren't yet able to say definitively how much of its track and development was as a result of climate change, it sounds the knell of what they've been warning about for years – more frequent and more intense storms.

According to meteorologists at Colorado State University's Tropical Meteorology Project, Irma set a new record for the amount of cyclone energy generated in a single day, and for maintaining wind speeds of 185 mph for 37 straight hours. That made it the strongest storm in the Atlantic.(Including the Caribbean and the Gulf of Mexico, it counts as the second strongest, after Allen, which reached 190 mph).

Also according to the team at Colorado State, on its own, Irma generated enough cyclone energy to satisfy the NOAA definition of an “average” hurricane season. Eighteen entire hurricane seasons since 1966 when satellite tracking of storms began, didn't generate as much total energy as Irma did.

The reasons for its record-breaking trek spanning the Leeward Islands to the east and the Florida panhandle in the west are due to multiple factors, chief of them appearing to be a combination of ocean heat content and sea surface temperatures.

Locally, principal director of government's Climate Change Division Una May Gordon told the Jamaica Observer yesterday that, “The warm sea surface temperature was fodder for Irma”.

“We can expect to see more of this a-typical weather activity with superstorms occurring more frequently accompanied by devastating floods and wind events,” she said.

“It means, therefore, that it will put our infrastructure under duress, especially water and drainage infrastructure built years ago,” said Gordon.

Seasoned meteorologist Evan Thompson was cautious about pinning Irma on climate change without definitive research, but he did not rule out the role of warming temperatures.

“It would not be possible to definitively say [at this point] that climate change was responsible for Irma's development; however, the projections of changes in weather occurrences because of global warming were reflected in what was experienced.

“Irma followed the script by developing so rapidly, being one of the most intense hurricanes on record and maintaining category 5 status for an inordinately long time. Over the years, those were just what we were told to expect in a changing climate scenario,” he reported.

Thompson, who is director of the Meteorological Service Division, explained that one of the main influences to tropical cyclone development is sea-surface temperatures exceeding 27 degrees Celsius, which was surpassed during the month of September.

“The rapid growth of Hurricane Irma to Category 5 status was most likely due to a number of factors. The main one is the warm sea-surface temperatures which were existent over the Caribbean and North Atlantic Ocean during the period. This is also the source of the high energy that allowed Irma to maintain Category 5 status for such a long time,” he told the Observer.

Also, he indicated that, “the environment under which Irma developed was one of low vertical wind shear. This allowed for the optimal mixing within the hurricane creating the dynamics that kept the system regenerating over time. If the shear had been stronger or more hostile it would have led to the break-up of the system [but] Irma's track over water for such a long time, except for moving over comparatively very small islands, was also why it continued to grow. It wasn't until it interacted with Cuba that it started to lose strength.”

Hurricane Irma was the ninth named storm of the 2017 Atlantic Hurricane season, and the fourth hurricane. It formed as a tropical wave off the west coast of Africa on August 26 and dissipated over south-eastern US yesterday, September 12.

It has been blamed for 55 deaths as of yesterday, and damage estimated at more than US$30 billion to date.