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(CNN) — The Atlantic hurricane season has had a quiet start, and experts say El Niño may be a major factor behind the lack of storm activity.
El Niño is a natural climate pattern marked by warmer-than-average sea surface temperatures in the equatorial Pacific, which can influence weather patterns around the world over extended periods.
The current El Niño was officially declared in June and could develop into a record-strength “Super El Niño” later this year.
Its effects are being seen through increased wind shear, which has disrupted tropical storm development and contributed to one of the quietest starts to the hurricane season since 2009.
Wind shear refers to changes in wind speed or direction at different levels of the atmosphere. It can weaken tropical systems or prevent them from forming altogether. In recent weeks, strong wind shear has affected the Caribbean Sea and the western Atlantic Ocean, areas that are typically favourable for tropical development.
“The number one calling card of El Niño is that wind shear,” said Michael Lowry, a Miami-based hurricane expert with CNN affiliate WPLG-TV.
According to National Oceanic and Atmospheric Administration data analysed by Lowry, wind shear over the Caribbean had its second-highest start to July since satellite records began in 1979.
Lowry said significant wind shear in the Caribbean and western Atlantic is one of the key indicators used to assess future hurricane activity.
While El Niño may not be solely responsible for the persistent wind shear since the season began on 1 June, experts say evidence increasingly points to it being a major contributor.
Meteorologist Matthew Rosencrans of NOAA said current wind shear patterns closely match what is typically expected during El Niño years, although detailed studies will be needed after the hurricane season ends in November to confirm the connection.
Experts say the atmosphere is complex, with global weather patterns and short-term conditions interacting in ways that can be difficult to separate.
However, signs of El Niño are also appearing in other large-scale atmospheric patterns, including the Walker Circulation, which can increase wind shear over the Atlantic during El Niño events.
The Walker Circulation involves rising and sinking air patterns that can either support or suppress storm formation. During El Niño years, warmer Pacific waters cause air to rise over the Pacific and sink over parts of the Atlantic basin, helping to limit tropical development.
Levi Silvers, a research scientist and co-author of Colorado State University’s hurricane forecasts, said the current conditions are consistent with what scientists understand about El Niño.
“I don’t think we can say exactly that current wind shear is for sure caused by El Niño, but I think it’s very likely that it is,” Silvers said.
The stronger wind shear could have implications for the peak of the hurricane season, which typically runs from mid-August through mid-October.
Research shows that higher levels of wind shear in the Caribbean and western tropical Atlantic during July are often linked to less active peak hurricane seasons, as developing storms are more likely to weaken before becoming organised systems.
Many pre-season forecasts had already predicted a quieter-than-normal hurricane season because of the expected El Niño conditions. With increasing confidence that a stronger El Niño could develop, some forecasting groups, including Colorado State University, have reduced their storm predictions further.
However, experts warn that threats remain, particularly closer to land in areas such as the Gulf of Mexico and the southeastern United States.
The only named storm so far this season, Tropical Storm Arthur, was a short-lived system that formed near the Texas coast in June but still produced dangerous flooding along parts of the Gulf Coast.
Although Arthur encountered wind shear, conditions were less hostile near the coast than they would have been farther south.
A similar pattern of wind shear has affected the Gulf of Mexico in recent days, but unusually warm ocean temperatures could provide energy for any system that develops.
Some forecast models indicate a possible tropical disturbance forming in the eastern Gulf early next week. Regardless of whether it develops into a storm, heavy rainfall remains the primary concern along Florida’s west coast.
While the second named storm typically forms around 17 July, experts say the season is not officially behind schedule. However, forecasts are becoming increasingly confident that overall storm activity may remain below average.
