What will "Super" El Niño mean for winter weather in Florida?

This August's weather was a bit maddening, and its continuing into September. Sure, coming off a prolonged drought, we needed the rain. But while it's been extra wet, it's also been extra unpredictable, with aggressive storm systems seeming to manifest at all hours with little warning.

Planning outdoor events or activities, or even deciding when to go on a walk or run, has become guesswork no matter how many weather forecasts one consults.  Needless to say, the convertible has been of little use lately.

The thunder has been excruciatingly loud, and some of the lightning bolts have seemed apocalyptic, even by "lightning capital of the world" standards. Sitting home while the skies opened once again, I decided to consult with the National Oceanic and Atmospheric Administration and try to figure out what exactly is going on. 

A "Super" El Niño?

An El Niño occurs when unusually warm water develops across the central/eastern equatorial Pacific and alters tropical thunderstorms and atmospheric circulation, changing the position and strength of the jet stream thousands of miles away.

What's been termed a "Super" El Niño has been strengthening rapidly, with NOAA placing the odds of a "very strong" El Niño this fall and winter above 90%. Even more remarkably, the agency currently estimates a 69% chance that the October–December 2026 period reaches a strength exceeding every El Niño on record, dating back to 1950.

Fewer Hurricanes?

In the good news department, an El Niño generally suppresses Atlantic hurricane activity by increasing upper-level wind shear across the tropical Atlantic. While that is merely a statistical tendency, a powerful El Niño usually makes the Atlantic environment less hospitable to tropical cyclone development.

In August, NOAA reported sea-surface temperature anomalies above +3°C in parts of the eastern equatorial Pacific, with the Niño-3.4 index around +1.8°C and enormous amounts of unusually warm water extending deep below the surface.

NOAA's forecast is essentially certain that it will persist through the winter: its August probabilities put El Niño at 100% January through March, 97% for February to April, and 82% even for March to May of next year.

An El Niño does not dictate individual storms or guarantee particular weather events, but patterns have persisted, and the stronger the El Niño, the more likely the classic El Niño pattern is to emerge.

Florida could see some of the strongest effects

Florida is one of the places where El Niño has a particularly recognizable winter signature: a stronger, more active subtropical jet stream across the Gulf of Mexico and Florida. That tends to send more storm systems across the Gulf and Southeast.

As a result, the Sunshine State may be a lot rainier than usual during what are usually Florida's dry months. If this El Niño actually reaches the strength levels NOAA currently projects, Florida could experience an unusually wet, active winter, with frequent Gulf storm systems and (like much of the U.S.) potentially more severe weather than usual.

Unfamiliar summer weather patterns

You've probably noticed that this summer's weather has been a bit atypical. June and July saw a lot of grey skies and thunder, but it often produced little to no actual precipitation. August has been very wet, but instead of the usual pattern of hot, sunny days followed by afternoon thunderstorms, morning and evening storm systems have been far more common than usual.

Here in the Tampa Bay region, strong daytime heating colliding with sea breezes usually makes thunderstorms most common in the afternoon and early evening. El Niño is likely part of the explanation for the far more scattered storm patterns that have emerged (I don't recall ever being awakened by so much early-morning thunder!).

While the developing El Niño has not been creating those thunderstorms, it is changing the larger atmospheric circulation in ways that can disrupt the Gulf Coast's summer thunderstorm rhythm.

NOAA says the atmosphere itself is now strongly coupled to the exceptionally warm Pacific, with convection shifting dramatically eastward, weakening the trade winds and changing upper-level circulation, while becoming the primary driver of anomalous upper-level winds and tropical convection across the globe.

So, while Florida's ordinary afternoon storms are largely thermodynamically driven (sunshine heats the land and the sea-breeze circulation triggers convection), disturbances moving through the atmosphere above Florida become dynamically forced.

Historical perspective

A stretch of ocean across the equator wider than the United States was hotter than it has ever been in August, a full 2.6 degrees above average. The closest comparisons are 1997 and 2015. In the third week of August, both years saw water along the equator that was 1.8 degrees warmer than average.

The winters that followed were devastating. In January 1998, an ice storm across New York and Canada left 4 million people without power for weeks. Six weeks later, tornadoes in Central Florida killed 42 people. That February, Los Angeles received a typical year's worth of rain in just one month.

In December 2015, a deadly tornado hit Mississippi on Dec. 23, while NYC hit 72 degrees on Christmas Eve. On Dec. 26, another deadly tornado hit, this time in Dallas. Just a month later, Winter Storm Juno put New York state under more than 30 inches of snow (including 10 inches in Central Park), while Baltimore experienced its biggest snowstorm in recorded history.

Again, those years saw August waters 1.8 degrees above average, while this year they were 2.6 degrees above average.