The mighty trade winds that ushered ships across the Atlantic when sails and Mother Nature set maritime agendas gave way in 2015 to the westerlies — gales that pile warm Pacific Ocean water against the Americas and signal El Nino.
But like a pendulum, that water will slosh back toward Asia. Trade winds will regain power. The subtropical jet stream that helped kill Atlantic hurricanes will shift south.
And La Nina will awaken.
Just as El Nino helped protect Florida from tropical cyclones this storm season, hurricane experts are already considering the fate of the U.S. coast in a La Nina year, which 2016 could easily become.
“After a really big El Nino, you seem to transition to La Nina, and it can happen rapidly,” said Bill Patzert, a climatologist at NASA’s jet propulsion laboratory in Pasadena, Calif. “The 2015 hurricane season was somewhat benign in the Atlantic, but if La Nina kicks in this coming summer, it could go back to spectacular.”
El Nino works as a hurricane deterrent by using the subtropical jet stream to cut the tops off storms with strong vertical shear — winds moving at different speeds and directions in different levels of the Atmosphere. The eastern Pacific Ocean is warmer than normal as surface waters flow west.
La Nina is marked by strong winds from the east that push warm Atlantic waters toward the U.S., while weaker winds from the west are less able to disrupt storms. The eastern Pacific Ocean is cooler than normal as east winds push surface water toward Asia.
During neutral years – between La Nina and El Nino – ocean temperatures, tropical rainfall patterns and wind patterns are closer to long term averages.
Colorado State University’s Department of Atmospheric Science stopped doing quantitative December hurricane forecasts for pending storm seasons in 2012.
But researchers are still issuing a more qualitative discussion of the factors that will influence the 2016 hurricane season, including the climatological chances that the U.S. and individual states will get hit by a tropical storm, hurricane or major hurricane.
This year’s discussion, released last week, relies on two main events for its hurricane predictions; whether El Nino will remain a strong influence through summer next year and the potency of the Atlantic Multi-Decadal Oscillation (AMO).
El Nino is known to knock down hurricanes by creating strong westerly wind shear, such as we saw during the 2015 hurricane season.
The AMO is a longer-term phenomenon that impacts sea-surface temperatures. Warm sea surface temperatures are like candy to growing hurricanes.
While CSU’s study, which was written by hurricane expert Philip Kotzbach with assistance from William Gray, looks generally at four scenarios affecting hurricane frequency and strength, it also gives climatological landfall probabilities for 2016. The probabilities are long term chances, taking into account data from the 20th century.
“While we are not issuing a quantitative forecast in this early outlook, we can still provide interested readers with the climatological probabilities of landfall for various portions of the United States coastline,” Klotzbach wrote.
For all of the U.S., Klotzbach said there is a 97 percent chance of a named storm making landfall. That could mean a tropical storm, hurricane or major hurricane.
Last week’s discussion also gives the climatological probabilities that a hurricane or major hurricane will impact specific states.
Klotzbach notes that none of the 27 major hurricanes that have formed since Wilma in 2005 made a U.S. landfall.
“The 10-year period that the U.S. has gone without any major landfalls exceeds the previous record of eight years set between 1861 and 1868,” he wrote.
“There is obviously a luck component that has played a significant role,” Klotzbach said.
He explains another part of why in a blog for the Capital Weather Gang written with Brian McNoldy. Basically an exploration of how an east coast low pressure system may be steering hurricanes away from the U.S.
Florida is singled out as being “remarkably lucky” to have not been impacted by a hurricane since Wilma. Klotzbach said there has been a marked decrease in hurricanes hitting the Florida peninsula over the past 50 years.
Bob Henson, a meteorologist and blogger for Weather Underground said CSU’s recent discussion makes him even more “eager to see how this very uncertain hurricane season will unfold.”
“As one would expect, the skill of these outlooks steadily improves as the hurricane season nears,” he wrote in a blog last week. “Even if it’s too soon right now to expect an accurate forecast for 2016, the latest thoughts from CSU make me even more eager to see how this very uncertain hurricane season will unfold.”