Early Predictions: The Transition From La Niña To Neutral

Weather Talk
Friday, May 27, 2011 - 1:22pm

The 2011 hurricane season has arrived, and just like the forecasters predicted, we have transitioned from a La Niña to a neutral phase. So what does this mean as far as activity is concerned? It would seem that a neutral phase would mean fewer hurricanes this season, but this may not be the case. It’s important not to put too much stock in the early season predicted numbers. Rather, it’s the time to prepare for the upcoming season regardless of preseason forecasts.

La Niña is characterized by cooler ocean waters located in the Central and Eastern Pacific. This is due to stronger easterly trade winds pushing the warmer water toward the west, allowing the cooler waters to rise to the surface. This creates less of a gradient between the cold air and water to the north and the now cooler water temperatures and air to the South. Therefore, in the middle of the two will be weaker upper level winds moving toward the Atlantic basin, which is conducive to tropical development.

El Niño is basically the total opposite. The easterly trade winds become weak which keeps the warm ocean water in place in the Central and Eastern Pacific. Therefore, there is a significant gradient between the cold air and water to the north and the warmer water temperatures and air to the south. This creates a gradient between the two, and can create very high winds in the upper levels moving toward the Atlantic basin which can rip off the tops of developing tropical systems.

A neutral is located somewhere in the middle, creating a normal weather pattern with no significant affects from ocean currents. El Niño will definitely decrease tropical activity in the Atlantic Basin, but how much of a difference is there between a La Niña year and a neutral phase? A valid question for sure, since La Niña has faded and has been replaced by a more neutral phase for this hurricane season.

The quote you may hear during this season, "La Niña, which causes more hurricanes, had turned into a neutral phase for this season. This means fewer hurricanes." As a meteorologist, I do not agree with this statement, because it gives a false sense of security for the upcoming season. There are a few things to consider as we journey through the 2011 hurricane season.

Let’s examine some storm numbers by season from 1995-2005, you can also reference the bar graph image for a more detailed view. During a La Niña phase there was an average of about 4 major storms formed during those seasons. Shockingly, there were actually more storms during a neutral phase (which we are currently in), than there were during the dreaded La Niña years, about 4.5 on average. There was a slight drop off for a Weak to Moderate El Niño phase. The biggest and most noticeable drop came during a Strong El Niño phase, which we are certainly not going to experience this season.

The second thing we need to understand is each season has a mind of its own. Each storm has a respective life journey. No one could have predicted the ridiculous activity during the 2005 season, or the incredible luck that the U.S. experienced during last year’s season. Nineteen named storms formed across the Atlantic in 2010. Twelve of those were hurricanes, and yet the U.S. was not affected by any of them. So although 2010’s prediction of being the one of the worst seasons in history was in fact true, as far as people affected by the systems it was over hyped.

In 1992 only seven storms formed, and only one land falling hurricane. However, that hurricane was Andrew. Although the numbers were down that year, it was one of the most devastating seasons in history as far as Louisiana and South Florida are concerned.

The same can be said for 2005, which was quite a year as far as storms go. Twenty-eight storms made their journey across the Atlantic, a staggering record that probably won't be touched anytime soon. Remember that La Niña is one of the causes of increased hurricane activity. 2005, however, was not a La Niña year.

Although it can be entertaining to read preseason predictions when it comes to each hurricane season, always remember prediction is not an exact science. Every season has a different story. Every storm has a unique lifespan. And these story lines cannot be written before June arrives. We must all just sit back, and watch how each season plays out.

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