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Tuesday September 2, 2014
Posted: Jun 03, 2014

El Nino forecast to make a comeback later this summer

The Maine Forecast — Tracking Maine’s weather patterns

This summer the big weather phenomena you will likely be hearing about from your favorite media outlet is El Nino.

El Nino which is poised to make a comeback after a hiatus of a few years can impact weather across the entire planet.  Just like this winter’s Polar Vortex, El Nino is a completely normal part of the atmospheric system and has been occurring for millennia.

 

El Nino occurs when the waters off the coast of South America warm above the long term average.   There are different regions of the El Nino which range from close to the coast to much further offshore.   Each El Nino is different.  Some El Nino’s like the “super El Nino” in 1998 can be so strong they spike global temperatures.  (see image above for spike during 1998.) Other El Ninos can be much weaker and have more subtle affects on global weather.

A stronger El Nino will typically bring more anomalous weather to the planet.  However, even a weak one can affect weather patterns enough to foster changes.  The line between individual events and seasonal weather is important to note.

Over the upcoming months and into next winter there will be major storms. Some will use and link these events to El Nino and in turn to climate change.  El Nino will certainly be a player in our upcoming weather patterns, but it’s very difficult to prove a causal relationship with a single event or the bigger issue of climate.

However, there are known weather patterns which typically manifest themselves during El Nino years.  These are patterns which result in drought, wetter conditions, cooler and warmer periods and fewer hurricanes hitting the eastern seaboard of the United States. 

Typically rainfall across the globe changes during an El Nino year.  As rainfall patterns shift, the crops that depend on the rain will perform poorer or in some cases better than normal.  According to forecasters in Australia, "A Northern Hemisphere summer El Niño tends to cause weaker than normal monsoons in India, wetter than normal conditions in Southern Brazil and also dry conditions through Eastern Australia. All of these factors will likely limit sugar supplies," You can see how this in turn could end up impacting food costs.

The impacts to the United States are also fairly well documented.  We do know summer weather is less affected by El Nino and La Nina than the fall and winter.  This is due to the fact summer weather isn’t a dramatic and widespread as that of the colder seasons.  In summer most of the United States experiences rainfall from showers and thunderstorms.  During El Nino the general pattern of these events can be disrupted bringing higher chances of more or less rain to a given area.   

The critical piece of all this is the word chance. The El Nino Southern Oscillation (ENSO) changes the odds of cooler/warmer and drier/wetter, but isn’t a switch guaranteeing an outcome.  The opposition of El Nino is La Nina.  This is when the water cools in the same region below normal.

During El Nino the trade winds are also impacted by the warming Pacific Ocean.  Normally, these winds carry tropical systems east to west towards the United States.  Depending on the strength of the El Nino the trade winds will weaken or even shift direction.  This will then limit the odd hurricane development and subsequent impacts to our coastline.  However, remember it’s just an odds game.  In 1992, during an El Nino year, hurricane Andrew, the most powerful hurricane to hit the United States in decades struck Florida.  No hurricane to hit the mainland has been stronger since then.   The map below shows some typical summer outcomes during an El Nino year.

Another benefit from El Nino is the increased likelihood of a break in the California drought.  During El Nino the jet stream tends to blow moisture from the Pacific into California and much of the southern United States.  The map below shows the chances of a wetter or drier winter throughout the lower 48 during an El Nino year.

Many scientists believe as the climate continues to change, El Nino may become more frequent and stronger. This could in turn bring about bigger shifts in our typical weather.

While a stronger El Nino would likely favor bigger spikes in precipitation, both up and down, weaker El Ninos would lead to less dramatic changes.

El Nino is highly likely to develop late this summer and most forecasters including Weatherbell Analytics and Colorado State University  favor a less active hurricane season as a result.  There is however still discrepancies in the strength of the upcoming El Nino, but most models agree this El Nino will approach moderate status, but not become an unusually strong one as happened back in 1998.

This past winter dragged on for many months and was reluctant to end.  If we do see an El Nino later this summer it will have impacts to our upcoming winter, but it’s still early to say exactly how.  Since El Nino years are often wetter, that could translate into another snowy season.  More on this during the summer and early fall.

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