Autumn begins in September with changes in weather

Photo of Gabriel Menchaca in Unsplash

Autumn arrives in September, with varying degrees of intensity depending on the region. Astronomically, the official beginning of this season in the Northern Hemisphere is marked by the autumnal equinox, which will occur on September 22 at 6:19 PM UTC in 2025, when the sun crosses the celestial equator and day and night are of equal length. This also represents the beginning of spring in the Southern Hemisphere.

From a meteorological perspective, autumn began earlier, on September 1, according to the criteria of seasons defined by complete months (September, October, and November).

In Latin America, the autumn experience varies considerably. In the Northern Hemisphere of Latin America (such as Mexico, Central America, and the Caribbean), the rains begin to intensify, and typical storms of the season are forecast, such as the San Francisco thunderstorm, which marks the transition from summer to rain.

In the Southern Hemisphere (e.g., Argentina, Chile, Uruguay, Paraguay), this season gradually brings cooler temperatures. In Paraguay, autumn begins while it's still warm, but southerly winds, fog, and cooler nights soon arrive. In Buenos Aires, September brings occasional thunderstorms, a drop in humidity, and temperatures between 2°C and 27°C.

Autumn begins with the La Niña phenomenon

At the global climate level, the World Meteorological Organization (WMO) warns that La Niña could reappear between September and November 2025, influencing weather patterns that could bring droughts or intense rainfall, particularly affecting agriculture, energy, and health in several regions, including Latin America. Seasonal forecasts predict above-average temperatures in much of the Northern Hemisphere, as well as western South America.

Although autumn formally begins at the end of September according to the astronomical calendar, its signs are felt from the first day of the month and vary according to latitude, geography, and global climate dynamics.

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Sources:

• Reuters