WRUF Weather

State of the Season: When and How an El Niño Might Take Over

The first four storms of the season formed within the first three weeks of the official 2012 Hurricane Season, making it the fastest season to four named storms since records have been kept.  However, the next five weeks were remarkably quiet, with not even a glimpse of a storm.  Like clockwork, however, August (a month with three times as many storms on average as July) has all of the sudden become quite active in the tropics.  Ernesto formed on the second day of the month, and two other disturbances have a decent chance of developing into our sixth and seventh named storms of the year over the coming days.

In the first part of our series, The State of the Season, we told you how a developing El Niño would likely impact the second half of our hurricane season.  We came to this conclusion in the same way we were able to give Floridians a warning that the season could start early and that the Nature Coast was long overdue.  It’s important to note, however, that the wide ranging effects from this ocean current are not expected to be in place until at least September.  And until El Niño takes hold, the tropical Atlantic will continue to be impacted by a number of other large-scale seasonal features, many of which were responsible for stifling the activity in July.

Large amounts of Saharan dust and the lack of deep convection (or thunderstorms) are two examples, both of which fluctuate over a weekly or monthly basis.  These features both play a role in accounting for only a small percentage of variability in cyclone formation, meaning they may be quite important at some points and relative non-factors at others.  Other factors, such as a developing El Niño, will affect large-scale tropical wind and temperature patterns over a longer range of time, sometimes lasting up to two years.  Just because these factors are bigger, though, does not mean they are much easier to predict.  The ENSO (or El Niño Southern Oscillation) exhibits considerable variability in strength and duration, and has only become well-understood in the past 25 years.

When the El Nino likely ramps up this fall, its intensity will increase just as the Atlantic Hurricane season nears its traditional September peak.  The ENSO is likely to create higher levels of wind shear over the Gulf and Southeastern U.S., dissuading development or steering a storm away from our coastlines.

Dr. Corene Matyas, Associate Professor of Geography from the University of Florida, has studied El Niño’s impacts on the tropics and explains why these winds play such a big role in a storm’s potential development.

“In the Atlantic Basin, you have winds coming in a different direction and at a faster speed at the top of the troposphere, and this interrupts storm development.  A nice tall column of warm, humid air is what is needed for a storm to form.  And when you have fast winds blowing across the top of that, the storms can’t develop to their full height.”

It must be noted that forecasting the formation of tropical cyclones in the Atlantic is notoriously difficult, largely due to a number of interlocking features that interact to produce variable conditions.  Dr. Matyas points out that just because a seasonal forecast may be for fewer storms, that doesn’t necessarily translate to weaker cyclones or fewer landfalls.

“Overall, activity tends to be lower during an El Niño.  That would mean U.S. landfalls tend to be lower, but that doesn’t mean they can’t happen.  And in the past, they have happened.”

And as stated in part one of this series, Floridians should remain “on guard” for potential activity affecting the state in the coming weeks, until it is evident the full effects of the El Niño current take over.  And even still, 20-years after Andrew, we’re reminded that it only takes one storm to cause damage and disrupt life, no matter how active the season is or forecast to be.

Other Stories from the “State of the Season” Series

Preface:  Floridians Should Be Prepared from Day One
Part One:  Early Signs a Developing El Niño May Tame the Tropics

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