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WRUF Weather: Developing El Niño May Tame the Tropics

By on July 18th, 2012

The 2012 Atlantic Hurricane Season began with a bang, spawning four named storms by June 27 and breaking numerous records, including the fastest start to an Atlantic hurricane season in history.  Two of the storms – Beryl and Debby – busted our extreme drought in North-Central Florida, brought considerable storm surge to the coastlines, dumped flooding rains on inland areas, and even spawned more than a dozen tornadoes.

WRUF was first to alert Floridians that the season would likely start early and that Florida’s coastlines were vulnerable.  The findings of this report back in May were based on research of prior years when a shift from a La Niña to an El Niño in the Eastern Pacific was occurring near the same time of year.  We are using that same methodology to see where things stand now that an El Niño is imminent.

Early forecasts from most experts were calling for a near-normal season of hurricane activity in the Atlantic, even as Beryl came ashore as the second named storm before the season officially began on June 1.  So the question is, with four storms already in the books, do these expectations need to be raised?  Since Debby’s deluge three weeks ago, the tropics have been largely quiet.  Most of the tropical waves have been suffocated by dry air or ripped apart by wind shear before they are able to form into storms, which may be a sign of things to come. The National Oceanic and Atmospheric Administration (NOAA), the National Hurricane Center’s parent body, issued its findings recently that the changes in water temperature off the coast of South America are indicative of a developing El Nino Southern Oscillation – ENSO or “El Nino” for short – one that could be in full effect by September.

The wide-ranging effects of this powerful, warm current sound like something out of a Hollywood movie. A strong ENSO event, which means an unusually warm and far-reaching current, has the ability to change weather throughout the entire hemisphere through a series of complex atmospheric interactions that are still not totally understood by climatologists. Its wide-ranging effects generally involve an increase in extreme weather, from crippling droughts and heat waves in some areas to increased severe thunderstorms and cold snaps in others. Due to its erratic and irregular nature, ENSO has only become well-understood within the last 25 years, and researchers have been trying to connect the dots between the capricious current and the equally volatile hurricane season ever since, with encouraging results.

It is believed that the developing El Nino current, currently weak but expected to strengthen, will pump large amounts of warm water into the normally chilly Pacific near the Equator. This warm water will cause atmospheric pressures to drop in the Pacific, creating a chain reaction involving monsoon-like areas of thunderstorms thousands of miles wide.  The end result for us will be a realignment of fast-moving upper-level winds in a southwest-to-northeast direction over the Gulf of Mexico and the Florida peninsula, likely to be in full swing by September.  These stronger winds aloft are forecast to create an environment unfavorable for tropical development south of 20 degrees latitude and west of the Leeward and Winward Islands during the second half of the season.

University of Florida and WRUF Forecaster Dan Henry discovered what may be one of the best pieces of evidence that our season may have already reached it’s climax.  He found six analogs to this year, which also featured frequent early activity and relatively quiet finishes.  While 1997 was an extreme case (the ENSO index was at a record high), it was almost an identical match to 2012′s pattern of storm development.  Five storms formed by July 16th, which at the time was a record, leading many to predict a destructive year. In the season’s remaining four and a half months, only three additional storms formed, none of which significantly impacted land – the least-active traditional season peak since 1929.

Dan also points out that most storms forming before August 31st in El Niño years develop near or make landfall in the Southeastern part of the United States.  However, less than 10 percent of storms in El Niño seasons threaten land from September on.  These findings strengthen our idea that Floridians should still be “on-guard” for early season activity in the coming weeks, but also that the chances for a land-falling storm will go down considerably during the second half of the season.

It’s important to remember that no two El Nino events are exactly alike, and with the majority of the hurricane season still ahead of us, it is impossible to say for certain how active our season will be. Even the most advanced computer models can only provide forecasts with any reliability for around two weeks in advance. With the recent unpredictable path of Tropical Storm Debby still very fresh in many Florida residents’ minds, it is clear that we must continue to remain prepared for any scenario, regardless of the potential presence or effects from the powerful and complex ENSO system.

Prepared in part by UF Forecaster Dan Henry


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