El Niño is the warm phase of a Pacific climate pattern called ENSO, the El Niño–Southern Oscillation. Trade winds weaken, and unusually warm water spreads toward the coast of South America. The opposite, cooler phase is La Niña. A single event often lasts about nine to twelve months and tends to peak in the northern-hemisphere winter.

The pattern is global, the hazard is local

A strong El Niño raises the odds of certain kinds of weather. It does not guarantee them, and it does not do the same thing on every continent.

• Often wetter: coastal Peru and Ecuador, and in many events parts of California and the southern United States, plus parts of eastern Africa.
• Often drier: Indonesia, northern Australia, the Amazon and northern South America, and parts of southern Africa. Some events also weaken the Indian monsoon.
• Storms shift: tropical cyclone activity in the Pacific tends to move, with fewer Atlantic hurricanes in many El Niño years and more activity toward the central and eastern Pacific.

Your town can still flood in a “dry” region, or stay mild in a “wet” one. Seasonal outlooks are odds, not a diary of the next six months.

What to do with that

Read the seasonal outlook from your national weather service before you buy anything. In the United States, the Climate Prediction Center at NOAA publishes those outlooks. Then prepare for the hazard that outlook actually describes.

• If the risk is heavy rain, start with drainage, flood insurance, and drinking water. Floods and dirty tap water arrive together more often than people expect.
• If the risk is drought or heat, start with stored water, shade, and a way to cope with power cuts during high demand.
• Either way, a family contact plan and a small food buffer are worth having. Roads and shops fail in both floods and wildfires.

The rest of this site is organized around those jobs: water and food, the house, power, and health. Pick the category that matches your local outlook, and do that one first.