It appears increasingly likely that La Nina conditions will develop in the central Pacific Ocean later this year, and that could have significant both short- and long-term impacts on New England’s weather later this year.
The opposite of El Nino, a La Nina means that sea-surface temperatures in the east-central Pacific Ocean are running cooler than average. In short, this creates a well-documented domino effect on global weather – including direct impacts on New England’s weather.
National Weather Service forecast models and official Climate Prediction Center (CPC) prognostications are indicating an increased probability of cooler-than-average sea-surface temperatures in the central-eastern Pacific Ocean this fall and winter. Last week, the CPC increased the odds of a La Nina developing this winter up to 45 percent – and lowered the odds of an El Nino event to just 10 percent.
El Nino and La Nina, known as the ENSO cycle, tends to have a big (although varying) impact on weather, particularly during the winter months.
La Nina tends to bring in colder and wetter winter weather to the northern United States, including New England. That’s because the polar jet stream tends to stay a bit further north during a La Nina winter, bringing in frequent waves of colder weather and snowfall.
The extent of those impacts is not equal and it depends in part on the strength and severity of the La Nina. It’s still far too early to tell how strong it might be, if a La Nina even develops.
In the shorter term, though, that could have an increased impact on the upcoming Atlantic basin hurricane season. The newly-released National Oceanic and Atmospheric Administration (NOAA) outlook for this summer’s hurricane season gives a 60 percent chance of a more active hurricane season than average, and a lack of an El Nino is a big part of the reason why.
Odds of #ElNino for peak of Atlantic #hurricane season (August-October) have dropped from 22% (with early April forecast) to 10%, per the latest outlook from NOAA. El Nino typically reduces Atlantic hurricane activity thru increases in vertical wind shear, especially in Caribbean pic.twitter.com/U8cLtf3V0V
— Philip Klotzbach (@philklotzbach) May 14, 2020
While hurricanes are relatively uncommon in New England, they do happen, and there’s been somewhat of an unusual drought from them in recent years. No hurricane has directly made landfall on New England since Hurricane Bob in 1991, although a then-weakened Hurricane Irene lashed western New England in 2011 and Superstorm Sandy had big impacts on southern New England in 2012.
A National Hurricane Center study found that hurricanes have a far better chance of having a direct landfall on the continental Untied States during non-El Nino years. While hurricane track widely varies, more activity, of course, increases overall odds of impacts from a tropical system.
With a possible La Nina potentially on the horizon, there are at least some hints that New England weather could be in for somewhat of a rollercoaster ride this year as a result of it.