Editor's note: This article was originally written in Chinese by Guo Zengyuan, senior engineer at China's National Climate Center. The article represents the author's opinion, not necessarily CGTN's.

The equatorial Pacific has been warming steadily since September, and Chinese climate monitors say it is on track to become the strongest El Nino on record, likely peaking around November.

Sea-surface temperatures in the central and eastern equatorial Pacific have risen more than 3 degrees Celsius above normal – the first time the index has crossed that level on record at the seasonal scale, according to China's National Climate Center. Forecasters expect the warming to keep fluctuating upward.

That raises an obvious question: A two or three degree swing in the air feels unremarkable, so how can a slightly warmer stretch of ocean disrupt weather around the world? Two things are easy to overlook.

First, El Nino is not a small patch of warm water. It is a temperature anomaly spanning a vast stretch of the equatorial Pacific, and it usually lasts for months. Second, the impact depends not just on how much the water warms, but on where. The tropical ocean is a key source of heat and moisture for the atmosphere. When the water is warmer, more moisture rises into the air, feeding clouds and rain – and that in turn changes where air rises and sinks. El Nino shifts those zones, rearranging winds, pressure and rainfall across enormous regions.

A seesaw across the Pacific

Normally, the equatorial Pacific is warm in the west and cool in the east. Trade winds blow from east to west, piling warm surface water up near Indonesia, while cold water from deeper down wells up in the east to keep it cooler. The warm west feeds rising air and heavy rain; the air then flows east at high altitude and sinks over the cooler east. This east-west loop is known as the Walker circulation.

During El Nino, those trade winds weaken. Warm water spreads toward the central and eastern Pacific, and the upwelling of cold water that usually cools the surface fades. The zones of thunderstorms and heavy rain shift east with it. The changes then reinforce one another: shifting pressure weakens the trade winds further, which pushes still more warm water east. Ocean and atmosphere feed on each other, which is why El Nino is not simply "warmer sea water" but a coupled process.

How a Pacific event reaches distant shores

El Nino forms in the tropical Pacific, yet its fingerprints show up in China, Australia and even North America. Scientists call this a teleconnection: an ocean or atmosphere anomaly in one place alters large-scale circulation, which carries the signal thousands of kilometers away.

Think of it as a line of falling dominoes. Warmer Pacific water changes air movement locally, shifting winds and pressure; those shifts spread outward, changing the moisture and storm tracks that reach other regions. El Nino can alter circulation over the western Pacific and East Asia, affecting rainfall in parts of China, and can bend the North Pacific jet stream, shifting storm activity and bringing unusual rain or temperatures to parts of North America.

Those effects are not uniform. They vary by season and region, and no two El Nino events produce the same outcome everywhere. The signal rarely stays confined to the ocean where it began.