A Record El Niño Is Rewriting Pacific Weather, and the Effects Reach Far Beyond It
The Pacific Ocean is warming unusually quickly, and this year’s El Niño has already passed previous records. Forecasters expect it to strengthen further before its usual peak around December. El Niño is the warm phase of a natural climate swing. It can bring drought to some regions and raise the risk of heavy rain and flooding in others. The reason sits in the Pacific’s warm water and the air above it.
In a typical year, trade winds blow from east to west across the tropical Pacific. They push warm surface water toward Indonesia and nearby seas. As that water moves west, colder water rises from below in the east. Scientists call that upwelling. Therefore, the western Pacific is usually much warmer than the eastern Pacific.
Warmer water evaporates more. The western Pacific feeds moisture into the air, and the ocean warms that air so it rises. Rising air lowers the pressure around it, then expands and cools. Water vapour condenses into clouds and rain, and releases heat into the atmosphere. High above the Pacific, some of that air spreads east and sinks over the cooler eastern Pacific. Near the surface, air flows back west as the trade winds. That loop is the Walker circulation.
This pattern helps explain heavy rain around Indonesia and a much drier eastern tropical Pacific and coastal Peru. Some parts of Indonesia can receive more rain in a month than Lima receives in a year. The pattern also reinforces itself. Warm water in the west encourages rising air, cooler water in the east favours sinking air, and the trade winds keep the contrast in place. Scientists call that mutual reinforcement the Bjerknes feedback.
El Niño breaks that script. The trade winds weaken, so less warm water is pushed west. More warm water stays in the central and eastern Pacific, and the western Pacific can turn relatively cooler. The zone of strongest evaporation, rising air, cloud, and rain then shifts east. Parts of the eastern Pacific, including coastal Peru, can turn much wetter. Meanwhile, sinking air over the western Pacific makes clouds harder to form. Indonesia and nearby areas can turn much drier, which can also raise the risk of forest and peatland fires. The smaller east-west temperature gap weakens the trade winds further, so the Walker circulation itself weakens and shifts east.
Those changes travel through teleconnections. Heat released when vapour condenses can warm the middle and upper tropical atmosphere far beyond the Pacific. Over the Sahel, on the southern fringe of the Sahara, that can make it harder for moist surface air to keep rising, which suppresses rain and can dry the land further. Scientists call this the tropospheric temperature mechanism. A second path is atmospheric ripples that change winds and storm tracks. Britain can see a higher chance of wetter, stormier weather in autumn and early winter, and a higher chance of colder spells later in winter. Those links are less certain than many tropical effects, because other drivers also shape UK weather. A third path runs through other oceans, including the Indian Ocean dipole, which influences rain over East Africa and parts of India.
El Niño shifts the odds. It does not decide every day’s weather. Thailand often leans drier during El Niño, yet parts of the country, including Bangkok, saw heavy rain and flooding this September. India has shown a similar contrast: the monsoon has been unusually dry overall this year, while some regions still saw intense rain and flooding. Local systems can still produce extremes in the other direction.
Recent images have already tied the event to local damage. High tides and large waves linked to El Niño were associated with a bluff failure in Encinitas, California, on September 18. Along Peru’s coast, environmental groups have warned that warmer Pacific water and shifting marine ecosystems are reducing fish available to seabirds.
Disclaimer: This article rewrites publicly reported climate explanations for general information only. It is not an official forecast. Local weather can differ from the regional tendency. Readers should check the latest meteorological bulletin before they act.