Phase vs Phase, 1950-2025 (ONI coverage)

ENSO Laboratory

What Even Is El Nino?

You cannot turn on the news during hurricane season without hearing "El Nino this" or "La Nina that" -- but almost nobody ever explains what the words actually mean. Here is the real answer.

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Steady winds called trade winds normally blow across the Pacific Ocean from east to west, all the way from South America to Asia. Think of it like blowing across a bowl of soup -- it pushes the warm broth toward the far side of the bowl. That is what the trade winds do to the ocean: they pile up warm water on the western side of the Pacific, near Asia and Australia, while cooler water rises up to replace it on the eastern side, near South America.

El Nino happens when those trade winds weaken. With less wind pushing it west, the warm water that was piled up near Asia sloshes back east, toward South America -- like letting go of that bowl of soup and watching it settle back to level.

La Nina is the opposite: the trade winds get stronger than normal, piling up even more warm water in the west and pulling up even more cold water in the east.

Neutral -- the most common state of the three -- is just... normal. Neither extreme. The soup sitting still.

Scientists call the whole system ENSO -- El Nino Southern Oscillation -- because there is a second half to the story: air pressure over the Pacific rises and falls in a seesaw pattern that mirrors the water temperature. That seesaw is actually the part that reaches all the way to Florida, thousands of miles from the Pacific -- not the warm water itself.

Here is the piece that matters most for this whole page: El Nino tends to increase wind shear over the Atlantic and Caribbean -- strong winds blowing at different speeds and directions at different altitudes, which can literally rip a forming hurricane apart before it gets organized. La Nina relaxes that shear, giving storms a clear, calm path to build and strengthen. That one mechanism is why the numbers below skew the way they do.

How do we know which phase we are in? NOAA tracks it with the Oceanic Nino Index (ONI), a running measure of Pacific sea-surface temperature. That record only goes back to 1950, which is why the comparison below is scoped to 1950-present.

The Numbers

Head-to-head comparison of the three ENSO phases across every hurricane season from 1950 to 2025. Raw counts alone mislead when the phases occur unequally often, so each column also shows how many total seasons that phase produced, and the share that brought Florida a hurricane. Storms before 1950 predate the ONI record and are listed in the Timeline without a phase.

Approach side is derived from the HURDAT2 track by a documented heuristic, not a NOAA-published field; see the methodology.

The 95% confidence range on each FL impact rate uses a Wilson score interval -- the standard textbook choice for a proportion at a modest sample size (dozens of seasons, not thousands), and one that never produces a nonsense bound below 0% or above 100% the way a plain +/- margin can. It answers "how much could this rate plausibly move with a few more or fewer seasons of data," not a claim about causation.

Storms Behind the Numbers

63 storms match. Phase filters cover 1950+ (ONI); the unfiltered list includes pre-1950 storms.

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The export carries every column above plus join confidence, pressure differences, and provenance fields, so the numbers can be verified independently.