Overall hurricane trends are up. The recent National Climate Assessment reports that over the past three decades, “the intensity, frequency and duration of North Atlantic hurricanes, as well as the frequency of the strongest hurricanes, have all increased.” MIT hurricane scientist Kerry Emanuel began looking at this effect back in 2005, when heMore
As the traditional peak of the Atlantic hurricane season nears, forecasters have slightly increased the number of storms they expect to see this year. While the figures still suggest near-normal activity, they would mark the busiest season since 2012 if they pan out.
The uptick in the forecast comes courtesy of shifts in the large-scale conditions that can foster or quash developing storms.
In its updated forecast released Thursday, the National Oceanic and Atmospheric Administration predicts the season will have 12 to 17 named storms (those that reach at least tropical storm strength). Of those, they expect five to eight to reach hurricane strength and then two to four of those to strengthen into major hurricanes (Category 3 or higher). Those numbers include the five storms that formed already this year.
NOAA’s May forecast predicted 10 to 16 named storms, four to eight hurricanes, and one to four major hurricanes.
“We’ve raised the numbers because some conditions now in place are indicative of a more active hurricane season,” Gerry Bell, the lead seasonal hurricane forecaster at NOAA’s Climate Prediction Center, said in a statement.
Among those conditions are the demise of El Niño, which tends to tamp down on Atlantic activity; vertical wind shear, or winds that move in different directions in different layers of the atmosphere, cutting off storm formation; and a strong African monsoon, which spits disturbances off the west coast of Africa that become the seeds of hurricanes.
There are some competing conditions that could serve to limit storms, though, such as stronger wind shear and sinking air over the Caribbean, and cooler ocean temperatures in the eastern Atlantic.
One factor that seems like it will have less of an impact on the season than was thought back in May is the La Niña that is potentially developing in the Pacific. La Niña tends to enhance Atlantic storm activity, but recent forecasts have slightly reduced the odds that it will form and if it does form, it is expected to form later and be weaker than previous forecasts.
In its update Thursday, NOAA put the odds of La Niña developing in the fall or winter at 55 to 60 percent. That likely means that it would arrive too late to have much impact on the hurricane season.
The 2016 season got an unusually early start with the formation of Hurricane Alex in January, the first January hurricane for the Atlantic since 1938. Tropical Storm Bonnie in May touched off a minor flurry of early season storms, including tropical storms Colin and Danielle. Late June ushered in a quiet period – due to dry air flowing off Africa -- only broken with the formation of Hurricane Earl, which became a named storm on Aug. 2.
“It's not unusual to have long gaps between activity early in the season,” hurricane researcher Phil Klotzbach, of Colorado State University, said in an email. Klotzbach’s own forecast is in the middle of the range of NOAA’s.
Earl made landfall in Central America as a Category 1 hurricane, dumping considerable rains on the area. Bonnie and Colin both impacted the U.S., which hasn’t seen a major hurricane hit since Wilma in 2005.
That record-long drought is mostly due to chance, researchers have said, and is somewhat subjective. Hurricane Sandy, for example, was a Category 1 hurricane when it made landfall in New Jersey, but it’s large size gave rise to a huge storm surge that caused extensive damage.
As the drought continues, hurricane forecasters and emergency managers are concerned that coastal residents have become complacent and that the many people who have flocked to the coasts in the past decade aren’t sufficiently aware of or prepared for the potential danger.
Booming coastal populations mean that more people and infrastructure are in harm’s way – a major concern as global warming-driven sea level rise exacerbates storm surge.
Forecasters can’t predict where hurricanes might strike this far in advance, as storm paths are largely governed by overriding weather patterns that are in place at the time they are active. They urge all coastal residents to be prepared, particularly as the peak of the season nears.
“We've still got a very long way to go in terms of overall activity,” Klotzbach said.