By Maeve Dunigan
According to a recent study released by the National Aeronautics and Space Administration (NASA), it has been ten years since a major hurricane has made landfall in the United States.
Of course, this isn’t to suggest that the U.S. has been immune to hurricanes during this same timeframe; Infamous examples include Hurricane Sandy’s devastation to the Northeast U.S. in 2012 and the financial hardships brought about by Hurricane Ike in 2008.
Yet neither of these storms met the definition of “major hurricane,” as defined by the National Oceanic and Atmospheric Administration’s (NOAA) National Hurricane Center (NHC). The NHC defines a major hurricane as a storm that reaches the classification of a category three or higher, with sustained winds at a minimum of 111 mph.
The recent “Cat3 hurricane drought” is according to NOAA, the longest period of time the United States has gone without a major hurricane since 1851, when storm occurrences were first recorded.
Although the decade-long respite from a category 3 storm might suggest a higher probability of a major hurricane occurring this season, NOAA can only estimate the expected numbers of storms for a given season, not their intensities.
NOAA reports that the 2016 season will most likely be near normal, with a 70 percent likelihood of 10 to 16 named storms – of which – four to eight could become hurricanes. However, NOAA also states that there is “forecast uncertainty” in the climate signals that influence the formation of Atlantic storms.
Some scientists suggest that a contributing factor in this uncertainty and in fact, the recent lack of hurricanes, could be due in part to El Niño.
Dr. Phillip Arkin, a research scientist and the deputy director of the University of Maryland’s (UMD) Earth System Sciences Interdisciplinary Center (ESSIC), described the lack of hurricanes and the presence of El Niño as having “a pretty clear connection.”
El Niño is the name given to the climactic variations that affect the equatorial Pacific, changes that make the water in this region warmer.
“The warmer than normal ocean temperatures affect the location of the convection in the tropical Pacific,” Arkin said. “One of the main outcomes of this change in convection is that you get eastward displacement of the jet streams in the northern hemisphere, and in particular you get a stronger than normal eastward flowing jet stream over the tropical Atlantic.”
Arkin said that the increased strength of this jet can lead to increased shear, or change in speed with height, in the Atlantic. Hurricane formation is suppressed in regions of strong shear.
“When people make forecasts of the number of hurricanes they look at the shear,” Arkin said. “And El Niño is a very strong influence [on shear].”
NOAA has recently reported the potential for a new variable in the hurricane equation in the form of El Niño’s counterpart, La Niña.
During La Niña, the average sea surface temperature across the equatorial Eastern and Central Pacific Ocean lowers by 3–5 °C.
In the latest El Nino/Southern Oscillation (ENSO) Diagnostic discussion issued by NOAA’s Climate Prediction Center, the synopsis favored a 75 percent chance of a La Niña during the fall and winter of 2016 and 2017.
However, a switch into a La Niña doesn’t automatically translate into an increase in hurricanes.
“La Niña doesn’t always have the reverse effect of El Niño,” Arkin said. “If we do get [a La Niña] it’s not as reliable a connection [for hurricane prediction] as El Niño.”
The 2016 season will encompass the period from June 01 – November 30, 2016.