Hurricane Matthew has killed hundreds in Haiti and is causing devastation as it churns up the southeast coast of the U.S., a massive storm fueled by unusually warm waters—1 to 3° F above normal in some places.
While it is too early to determine how climate change shaped Matthew—that will involve computer modeling and other historical analyses—we know that this is an unusual storm, and we can pinpoint a few general ways in which global warming could be contributing to its strength.
Warm water fuels hurricanes, and over the past week, water temperatures have been about 85° F in the Caribbean where Matthew first intensified. While that is a little above normal, the water off the Atlantic coast is even warmer when compared to the seasonal normal. Average ocean temperatures have risen over the last century, with parts of the Atlantic now 1-2°F warmer than a century ago. While warm water isn’t the only factor that determines how strong a hurricane can get, it is a key ingredient.
There is the expectation that hurricanes and typhoons across the globe will last longer and produce more rain by the end of the century, according to the research compiled in the 2013 IPCC Fifth Assessment Report. In addition, the frequency of the most intense storms may increase, but the overall number of hurricanes may not necessarily increase.
On top of that, sea level rise, which is already occurring and is well documented, will make the coastlines more vulnerable in the coming decades to the storm surges that accompany hurricanes. Already, over the last century, greenhouse warming has added about eight inches of sea level rise. Taken together, studies on future sea level rise forecast an additional 3 feet of rise by the end of the century. As a result, even if there were no increase in the strength of hurricanes, the amount of potential damage from their flooding storm surge, when compounded by sea level rise, would increase.
Matthew’s path has also been unusual, although it does bear some resemblance to Hazel in 1954. Matthew has been the only hurricane on record to make landfall as a Category 3 or stronger storm in Haiti, Cuba, and the Bahamas.
The major hurricane drought in the U.S.—no major hurricane coming ashore since Wilma in 2005—has largely been a fluke of the steering winds when the hurricanes have formed. (Again, remember that Sandy, despite the devastation, didn’t count as a “major” hurricane.) The hurricane seasons since 2005 have been active, and landfalls have occurred in other parts of the Atlantic basin, including Mexico and the Caribbean Islands.
Scientists will also be closely watching what happens after today. Initially, it was believed that Matthew would take the climatologically favored track of a northeastward turn, hugging the coast of the Carolinas and then heading out to sea. This often happens as a hurricane drifts northward until reaching the westerly steering winds of the jet stream. But over the past day or so, the models predict that this track less likely to happen. The jet stream winds travel in waves, and it was hoped that one of the waves would dip far enough southward toward Matthew to effectively grab it and whisk it offshore. Most of the available computer simulations now suggest that the dip in the jet stream will bypass Matthew to the north, leaving it to drift off the Southeast Coast for at least a few more days.
Perhaps most distressingly, some of these simulations indicate that Matthew could take a circular course, revisiting east coast of Florida next week. It’s a disturbing scenario, but it’s important to remember that five-day position forecasts for hurricanes can err by more than 200 miles, so it’s by no means certain this will happen. Even if it does, the environment will no longer be favorable for the storm to maintain its current strength, so a full-fledged double whammy to the Florida coast is not likely.
In the coming weeks, as scientists start probing climate change’s role in fueling Matthew, they will also be investigating its remarkable growth.
It is unusual for a hurricane to maintain the intensity that Matthew has had this late into the season. According to Phil Klotzbach, the hurricane researcher at Colorado State, Matthew is the longest-lived major hurricane on record forming after September 25 in the Atlantic basin. (Semantics can be tricky. By definition, a major hurricane is a Category 3 (Winds of 111 mph) or stronger, and while storms like Sandy in 2012 and Hermine earlier this year had huge impacts, their wind speeds did not qualify them as a major hurricanes.)
Klotzbach also indicated that the speed at which the storm intensified was unusual, having the third strongest 24-hour intensification on record in the Atlantic, going from a Category 1 to 5 on September 30.
One measurement of a storm’s duration and intensity is called Accumulated Cyclone Energy (ACE), which takes into account a hurricane’s winds over time. Matthew has generated the most ACE by any Atlantic hurricane in over a decade, according to Klotzbach. And before it fades away—which could be several more days—it may be one of the highest ACE generators in the last half-century.