01:04 El Nino, La Nina And Tornadoes A long-range seasonal prediction of severe thunderstorm activity can be gathered from changes in El Nino-La Nina cycles months in advance. Matt Sampson has the details.

El Niño is intensifying much earlier than usual this summer and may become the strongest on record in the modern era later this year. That may play a significant role in your weather through the winter and spring.

<img class="styles__noscript__2rw2y" src="https://dsx.weather.com//util/image/w/SST-anoms-11jul15.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0" srcset="https://dsx.weather.com//util/image/w/SST-anoms-11jul15.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 400w, https://dsx.weather.com//util/image/w/SST-anoms-11jul15.jpg?v=ap&w=980&h=551&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 800w" > El Niño SSTs - July 11, 2015 Weekly sea-surface temperature anomalies from July 5-11, 2015 in degrees Celsius. The classic El Niño signature of warm anomalies is shown in the boxed areas. (NOAA/ESRL/PSD) (NOAA/ESRL/PSD)

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/El-Nino-IRI-July2015-forecasts.jpg" srcset="https://s.w-x.co/El-Nino-IRI-July2015-forecasts.jpg 400w, https://s.w-x.co/El-Nino-IRI-July2015-forecasts.jpg 800w" > Model forecasts of sea-surface temperature anomalies in the Niño 3.4 region as of mid-July 2015. The majority of models forecasted a strong El Niño. A number of solutions even forecast this El Niño to top the modern record strength El Niño from 1997 (2.3 degrees Celsius anomaly). (IRI/CPC) (IRI/CPC)

El Niño, an anomalous, yet periodic, warming of the central and eastern equatorial Pacific Ocean, was firmly entrenched as of mid-July across a wide swath of the equatorial Pacific basin from off the northwest coast of South America to the International Date Line.

Weekly sea-surface temperature anomalies in the so-called Niño 3.4 region , a strip of near-equatorial Pacific Ocean water scientists monitor for El Niño (and its anomalously cold opposite, La Niña), had climbed to 1.5 degrees Celsius above average in early July, the threshold for a strong El Niño if persisting for a three-month timeframe.

Furthermore, this El Niño is expected to continue intensifying into the upcoming fall or winter and may persist into spring 2016. Most El Niños last 9-12 months.

Long-range model forecasts from NOAA, the U.K. Met Office, Australia's Bureau of Meteorology, and the European Centre for Medium Range Weather Forecasting, among others, all suggest the current El Niño is not only a virtual lock to be strong, but may eventually rival the strongest in modern records dating to 1950, with anomalies approaching or exceeding the 2.3 degrees Celsius observed in late 1997.

This may place the El Niño of 2015-2016 in the discussion with the "Super El Niños" of 1997-1998 and 1982-1983.

In fact, the latest available three-month mean sea-surface temperature anomalies in the Niño 3.4 region – April through June – were pacing 0.3 degrees Celsius warmer than the corresponding period in both 1997 and 1982.

Before we examine those previous cases, let's explain how anomalously warm water in this region matters for weather impact elsewhere.

Changing the Atmospheric Circulation

Typically, easterly trade winds near the equator pile warm water into the western Pacific Ocean. Conversely, the resultant upwelling, or upward movement of deep, cold ocean water keeps the eastern and central Pacific Ocean cooler.

Thunderstorms require at least some degree of warm, humid air near the surface, so they're more numerous and persistent over the western Pacific warm pool, and much less so in the eastern equatorial Pacific.

During an El Niño, these trade winds weaken, and may at times reverse from easterlies to westerlies. Warmer western Pacific water then slowly sloshes back toward the central, even eastern Pacific Ocean in what's known as an equatorial-trapped oceanic Kelvin wave.

Therefore, the most persistent thunderstorms will shift from the western to the eastern and central Pacific Ocean in an El Niño.

This trade wind reversal and the resulting reorientation of thunderstorms changes the atmospheric circulation not just over this swath of the equatorial Pacific Ocean, but can also have far-reaching impacts on the atmospheric circulation.

In general, warmer ocean anomalies spread over a larger area lead to a stronger forcing to the atmosphere.

<img class="styles__noscript__2rw2y" src="https://dsx.weather.com//util/image/w/elnino-atl-trop-shear.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0" srcset="https://dsx.weather.com//util/image/w/elnino-atl-trop-shear.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 400w, https://dsx.weather.com//util/image/w/elnino-atl-trop-shear.jpg?v=ap&w=980&h=551&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 800w" > Stronger El Ninos can produce greater wind shear over parts of the Atlantic Basin, particularly the Caribbean Sea.

For instance, the subtropical, or southern branch of the jet stream is typically more robust in a strong El Niño, leading to increased wind shear in parts of the Atlantic Basin. This is one factor, along with dry air, that limits the development and strengthening of tropical cyclones.

In fact, we've already seen record early June through early July wind shear over the Caribbean Sea, according to Colorado State University tropical scientist Phil Klotzbach . Klotzbach also tweeted the late June-early July wind shear in the Caribbean was stronger than the average shear in January .

Conversely, a hyperactive eastern and central Pacific hurricane season often accompanies a strong El Niño, helped by bursts of anomalous west winds near the equator lending extra spin to developing tropical cyclones in those basins.

(MORE: Record Start to Hurricane Season )

This invigorated subtropical jet also plays a significant role in the colder months during a strong El Niño. To illustrate that, let's take a closer look at the temperature and precipitation patterns from the two past "Super El Niños."

Super El Niño Flashbacks

Before we begin, a few disclaimers are in order with regard to impacts:

1) El Niño is not the sole driver of the atmosphere at any time. Day-to-day variability in the weather pattern, including blocking patterns, forcing from climate change and other factors all work together with El Niño to determine the overall weather experienced over the timeframe of a few months.

2) Impacts discussed are those typically expected, but they aren't always the rule. No two El Niños are exactly alike.

El Niño's clearest impact on northern hemisphere weather patterns occurs from late fall through winter.

"The only good analog for the current situation is the very strong El Niño event of 1997," wrote Dr. Todd Crawford, chief meteorologist of The Weather Channel Professional Division in a seasonal outlook released July 17.

Despite the disclaimers above and the rather small sample size of only two El Niños that may be of a magnitude comparable to 2015-2016, let's examine those two previous über cases to see if we can find any commonalities in U.S. impacts.

Precipitation

There are some broad similarities, and a few differences in the colder season precipitation patterns from the two previous strongest El Niño events.

<img class="styles__noscript__2rw2y" src="https://dsx.weather.com//util/image/w/EN-precip-8283-9798.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0" srcset="https://dsx.weather.com//util/image/w/EN-precip-8283-9798.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 400w, https://dsx.weather.com//util/image/w/EN-precip-8283-9798.jpg?v=ap&w=980&h=551&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 800w" > November-March precipitation anomalies during the two "Super El Niños" of 1982-1983 (left) and 1997-1998 (right). (NOAA/ESRL PSD, CIRES-CU) (NOAA/ESRL PSD, CIRES-CU)

Let's start with what was common with both, lending somewhat higher confidence to a seasonal forecast:

Very wet: California, Deep South, Gulf Coast, Florida, Southeast coast

California, Deep South, Gulf Coast, Florida, Southeast coast Wet: Plains to western Great Lakes, Desert Southwest, southern Great Basin, Northeast seaboard

Plains to western Great Lakes, Desert Southwest, southern Great Basin, Northeast seaboard Dry: Parts of Tennessee into the Ohio Valley, parts of Montana

(WATCH: Paul Walsh on Potential California Economic Impact )

The energetic southern branch of the jet stream mentioned earlier is a significant contributor to the overall wet southern tier we've seen in the past two "Super El Niños".

There are some key differences that diminish confidence in an outlook based solely on a strong El Niño:

Pacific Northwest: Wet in '82-'83, but quite dry in '97-'98

Wet in '82-'83, but quite dry in '97-'98 Interior Northeast (Virginia to Vermont): Near average or dry in '82-'83, but quite wet in '97-'98

Near average or dry in '82-'83, but quite wet in '97-'98 Mid-South (eastern Arkansas, west Tennessee, northern Mississippi): Wet in '82-'83, but quite dry in '97-'98

Residents of the western states may remember the flooding that struck California during the strong 1997-1998 El Nino. In February 1998, a series of storms caused an estimated $550 million in damage and killed 17 people in California. A total of 35 counties were declared federal disaster areas. This fits into the bucket of the wetter-than-average winter you would typically expect in a moderate or strong El Niño.

Interestingly, during the previous winter there was also major flooding in California and it was even more costly with a total price tag of $1.8 billion, according to Jan Null, a consulting meteorologist in California . However, El Niño was not present that winter and rainfall for the season was near average. The flooding was the result of excessive rainfall that fell in a short time period combined with snowmelt from late December to early January.

So, those hoping for drought relief next winter in the Golden State shouldn't immediately draw a conclusion that significant rains are ahead in any El Niño year. The strength of the El Niño can play a role in the outcome. In addition, heavy rainfall can occur with or without El Niño present and that was the case in the winter preceding the strong 1997-1998 El Niño.

Temperatures

<img class="styles__noscript__2rw2y" src="https://dsx.weather.com//util/image/w/EN-temps-8283-9798.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0" srcset="https://dsx.weather.com//util/image/w/EN-temps-8283-9798.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 400w, https://dsx.weather.com//util/image/w/EN-temps-8283-9798.jpg?v=ap&w=980&h=551&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 800w" > Super El Ninos: Nov-Mar Temperature Anomalies November-March temperature anomalies during the two "Super El Niños" of 1982-1983 (left) and 1997-1998 (right). (NOAA/ESRL PSD, CIRES-CU) (NOAA/ESRL PSD, CIRES-CU)

These are more straight-forward and less prone to disagreement.

Generally speaking, both events featured warmer-than-average temperatures from November through March along the northern half of the U.S. from the Pacific Northwest to the Northeast.

Particularly warm in both events was a swath from the northern Plains to the Great Lakes.

Incidentally, this warmer late fall and winter in a strong El Niño doesn't necessarily correlate to less snow in all locations, as NOAA's Climate Prediction Center laid out in a series of bar graphs .

On the other end of the spectrum, parts of the Desert Southwest, southern Rockies and southern High Plains were a tad cooler than average in both events. The general wet southern tier contributed somewhat to the near or slightly below-average temperatures.

Atlantic Hurricane Season

There was a clear reduction in the number of Atlantic named storms and hurricanes in the season encompassed by each past "Super El Niño."

In 1982, only six storms formed, two of which managed to become hurricanes.

<img class="styles__noscript__2rw2y" src="http://icons.wxug.com/data/dhc_archive_charts/at_1982_charts/at1982.gif" srcset="http://icons.wxug.com/data/dhc_archive_charts/at_1982_charts/at1982.gif 400w, http://icons.wxug.com/data/dhc_archive_charts/at_1982_charts/at1982.gif 800w" > Tracks of all named storms, including an unnamed subtropical storm, in 1982. (Weather Underground) (Weather Underground)

With that El Niño carrying over into early summer the following year, the 1983 season only produced four named storms and two hurricanes. One of these, however, was destructive Category 3 Hurricane Alicia .

<img class="styles__noscript__2rw2y" src="http://icons.wxug.com/data/dhc_archive_charts/at_1983_charts/at1983.gif" srcset="http://icons.wxug.com/data/dhc_archive_charts/at_1983_charts/at1983.gif 400w, http://icons.wxug.com/data/dhc_archive_charts/at_1983_charts/at1983.gif 800w" > Tracks of all Atlantic named storms in 1983, including destructive Hurricane Alicia. (Weather Underground) (Weather Underground)

The 1997 season was also relatively muted in numbers, with only eight named storms, though Hurricane Danny did make landfall along the northern Gulf Coast.

<img class="styles__noscript__2rw2y" src="http://icons.wxug.com/data/dhc_archive_charts/at_1997_charts/at1997.gif" srcset="http://icons.wxug.com/data/dhc_archive_charts/at_1997_charts/at1997.gif 400w, http://icons.wxug.com/data/dhc_archive_charts/at_1997_charts/at1997.gif 800w" > Tracks of all Atlantic Basin named storms in 1997. (Weather Underground) (Weather Underground)

With the 1997-1998 El Niño wrapped up by late spring, the 1998 hurricane season was much busier, with 14 named storms and 10 hurricanes, including retired Hurricane Georges and Hurricane Mitch .

Not only did 1982, 1983 and 1997 all feature a dearth of Atlantic storms, but none of them formed or tracked into the Caribbean Sea, harkening back to the increased shear we discussed earlier.

Furthermore, only two of those storms -- Beryl '82 and Erika '97 -- formed in the main development region, a common breeding ground for Atlantic tropical cyclones between west Africa and the Lesser Antilles.

The large majority of those named storms during those three strong El Niño seasons formed either in the western Atlantic Ocean or Gulf of Mexico.

Despite the likely lower numbers of named storms, it only takes one landfall to erase hopes of a "quiet season", as we saw with 1983's Hurricane Alicia in southeast Texas .

Two of the first three named storms in the 2015 Atlantic hurricane season -- Ana and Bill -- made U.S. landfall.

So, keep these general tendencies of strong El Niños in mind, but don't take them to the bank. There are other atmospheric players that could pull the strings, at times, this fall, winter and spring.

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