(NOAA)

The National Weather Service (NWS) finally announced publicly today what some other forecasters have said for months: the burgeoning El Nino event has a good chance to be a strong one by the fall or winter.

“[F]orecasters currently favor a ‘strong’ event for the fall/early winter,” writes Emily Becker of the National Weather Service Climate Prediction Center on NOAA’s ENSO blog.

ENSO stands for the El Nino Southern Oscillation, in which ocean temperatures and in central and eastern tropical Pacific alternate between warmer and cooler than normal states, El Nino and La Nina, respectively.

The NWS still heavily qualifies its strong El Nino prediction, stating strength forecasts are “the most challenging aspect”. But it says the odds of a weak or moderate El Nino or no El Nino are slipping.

In previous months, the cautious NWS refused to make a forecast for El Nino’s fall and winter intensity, citing a “spring predictability barrier” that it said made strength forecasts unreliable.

Meanwhile, a number of independent forecasters at universities and in the private sector were gung-ho for a strong event or even a historic or “super” El Nino – along the lines of the 1982-1983 and 1997-1998, the strongest on record.

[Models and experts lean toward strong El Nino forecast for the fall]

Becker’s blog post says a number of El Nino indicators point in the direction of a strong event, including warming sea surface temperatures “all across” the tropical Pacific, a weakening of surface trade winds, and signs of a new west to east push of warm water under the ocean’s surface called a Kelvin wave.

Becker adds computer model, on average, also forecast a strong event.


Computer model forecast for sea surface temperature difference from normal in the central and eastern Pacific. Levels over 1.5 C above normal indicate a strong event. (NOAA)

As forecasters have only observed El Ninos for a few decades, Becker cautions “there’s still plenty of uncertainty about how it will evolve.”

Despite reservations about the strength forecast, the NWS expressed high confidence El Nino will continue through the fall (over a 90 percent chance) and into the winter (85 percent chance).

Should a strong El Nino materialize, some of the key impacts you’re likely to hear about include:

1) An elevated chance of above normal precipitation in California this winter
2) Increased Pacific hurricane and typhoon activity
3) Decreased Atlantic hurricane activity
4) A mild winter for the northern tier of the U.S.
5) Somewhat less tornado activity in the U.S. compared to average

[Five ways a strong El Nino could affect our weather]

From much-needed California rain to a quiet hurricane season, Capital Weather Gang's Jason Samenow explains how a strong El Niño could affect U.S. weather. (Gillian Brockell and Jorge Ribas/The Washington Post)

A strong El Nino also means it’s extremely likely 2015 becomes the warmest year on record for the globe given all of the warmth in the Pacific.

We’ll take a closer look at what a strong El Nino may portend for the Mid-Atlantic in future posts.