El Nino, La Nina trade places

Last year was El Nino. This year it’s been La Nina.

The swing of the ENSO index to either of its La Nina/El Nino extremes is perhaps the best known teleconnection and most reliable predictor of dry season rainfall in south Florida.

That’s shown clearly in the above graph.

It plots south Florida’s dry season rainfall ranked from lowest (~5 inches) to highest (~28 inches) for the past 110 years, going all the way back to 1896. El Nino years are highlighted in red and La Nina years are highlighted in blue.

The trend is unmistakable.

El Ninos portend wet dry seasons (often topping 20 inches) and La Ninas are just the opposite: dry and often below 10 inches.

But you can throw the rule book out the window for the past two dry seasons.

Or at a minimum, we have to consider them as extreme (and remarkable) exceptions to the historic rule!

2006-07 set the record for the lowest (driest) dry season rainfall during an El Nino year.

Now it looks like 2007-2008 dry season could set the record for the highest (wettest) La Nina year (discounting the 1998-99 anomaly with high Nov’88 rain from T.S. Mitch).

All we need is an additional 0.15″ more rain in the next 3 weeks will move 2007-08 from 3rd to 2nd highest; and adjusting 1998-99 for T.S. Mitch could make 2007-08 the wettest-ever La Nina dry season.

This post was contributed courtesy of Cal Neidrauer and Paul Trimble from the South Florida Water Management District.

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