As temperatures warm up and the school year winds down for kids across the country, people are eager for summer to arrive before spring has a chance to set in. Everyone wants to know what kind of weather we’ll have this summer, but there’s one factor that could have some consequences: El Niño.

The warming and cooling of the eastern equatorial Pacific Ocean around the northwestern coast of South America is called the “El Niño Southern Oscillation,” or ENSO for short. Aside from an awesome Saturday Night Live character played by Chris Farley, El Niño is the abnormal warming of these waters around the equator, while La Niña is the abnormal cooling of the same. If you were wondering, “El Niño” is so named because residents first noticed it around Christmas, so the phrase (which translates to “the little boy”) refers to baby Jesus.

An El Niño occurs when the water in four regions of the east-central Pacific is (on average) 0.5°C warmer than normal for three consecutive months. Forecasters seem to have a hard time predicting when an El Niño will occur (remember last year’s “Super El Niño” that didn’t happen?), but with technologies available today, it’s pretty easy to determine when one is ongoing, as is the case right now.

The latest update from the Climate Prediction Center indicates that we’re seeing a weak El Niño in the Pacific Ocean right now—today’s sea surface temperature anomaly chart shows the abnormally warm waters sitting off the coast of Ecuador.

Assuming this weak El Niño stays on course through the summer (CPC gives it a 70% chance of doing just that), what will it do to our summer weather in the United States? Folks in the western half of the country are especially familiar with the wintry effects of this oceanic warming, as a very strong event resulted in devastating flooding in California during the winter of 1997-1998 (caution: PDF file).

The current warming event is relatively weak, so its effects won’t be as defined as if it were the “Super El Niño” we hear hypothesized/predicted every couple of years. That being said, we could still see some noticeable effects here in the States.

Hurricanes

The most heavily-advertised summertime effect that El Niño has on weather in the United States (and countries surrounding the Atlantic Ocean) is the relative lack of hurricanes that form on El Niño years. Warmer equatorial waters help strengthen the sub-tropical jet stream and foster convection over and near the Pacific Ocean, creating strong westerly winds in the upper levels of the atmosphere. This wind shear can bathe the Gulf, Caribbean, and western Atlantic during hurricane season, shredding any whiff of a storm before it has a chance to get its act together.

We can usually expect below-normal tropical activity in the Atlantic (and above-normal activity in the Pacific) during El Niño years, but it only takes one storm to make a mess. The 1992 hurricane season was an especially quiet season—the first named storm didn’t form until late August!

That storm, however, was Hurricane Andrew.

Even if the season is predicted to be quiet, make sure you have a plan and supplies in place and take quick action if you have to get out of the way of a storm.

Temperatures

Aha! Temperatures, the one factor most people care about. Well, bad news.

El Niño events don’t really have a noticeable impact on summer temperatures in the United States, so we have to rely on other factors in the atmosphere to give us hints as to what will happen.

For the first half of the summer, the Climate Prediction Center expects more of the same, with warmer-than-normal temperatures along the West Coast (naturally) and in southern Florida, where they recently experienced all-time record heat for April. Texas has a slightly elevated chance of seeing below-normal temperatures, but as for everyone else, we have equal chances of seeing above, below, or just plain normal temperatures for May, June, and July.

It’s worth keeping in mind that these forecasts are just a guide, and since these are extended-range outlooks (for which there isn’t much skill), there’s a good chance they could be wrong. It’s one of those things where we still have to look at it on a week-by-week basis.

Precipitation

We also don’t see too much of a change in precipitation during these events, but some areas could be in for higher-than-normal amounts of rain if this weak El Niño can start to mess with weather in the eastern Pacific.

The drought is a major issue around the country—as of this Tuesday, more than half of the country (53%) experienced “abnormally dry” or drought conditions, with the worst drought in California, Nevada, and around the Red River in Texas and Oklahoma. Any hint of rainfall is a positive step, but too much all at once is a bad thing.

Increased convection in the eastern Pacific Ocean could give rise to more atmospheric rivers—a ribbon of moisture in the mid-levels of the atmosphere, which occur around the world on a daily basis—which would help transport tropical moisture towards the United States and lead to a higher potential for heavy rain in thunderstorms.

Any uptick in tropical activity in the eastern Pacific Ocean increases the chances that we could see the remnants of a tropical system move north into the southwestern United States, which could bring beneficial (but likely flooding) rainfall to places that desperately need it. The most likely track of storm remnants is up the Gulf of California towards Arizona, or across northern Mexico into places like New Mexico or Texas.

None of these effects are guaranteed, especially when the El Niño is as weak as the one we’re currently experiencing, but it serves as a guide that gives you a peek at what we could see this summer. The warming event could start to tick up in intensity over the next couple of weeks—Eric Holthaus tweeted a great animation of warmer waters lurking just beneath the surface—but things can change in the blink of an eye.

[Images: NASA, NOAA, NOAA, CPC, author]

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