From the beginning of winter until the end of 2/2026, northern Vietnam experienced about 13 cold spells, but most were not strong or prolonged. Cold periods often alternated with phases of rapid temperature increase, resulting in a higher-than-normal average seasonal temperature. Statistics for the three main winter months (12/2025-2/2026) show average temperatures in many areas were about 0,1-2 degrees Celsius higher than the multi-year average.

According to Dr. Truong Ba Kien, Deputy Director of the Climate Research Center at the Institute of Meteorology, Hydrology, Environment and Sea Science, this winter was influenced by several large-scale climate factors.

People in Hanoi during the winter of 2026. Photo: Giang Huy

Primarily, the atmospheric circulation system in the Northern Hemisphere saw significant fluctuations. The polar vortex, a strong wind ring around the Arctic responsible for confining cold air to the polar region, weakened and deformed due to sudden stratospheric warming. "When the polar vortex is disrupted, the high-altitude jet stream also changes, becoming more wavy. This makes the path of cold air masses less stable than usual," Mr. Kien explained.

This alteration meant that cold air masses did not follow their familiar trajectory from Siberia towards East Asia. Instead, during the past winter, many strong cold spells moved deep into North America, causing extreme cold and snowstorms in that region.

Meanwhile, in Eurasia and the West Pacific, the presence of high-pressure systems diverted cold air flows from Siberia southward. Consequently, East Asia and Southeast Asia, including Vietnam, experienced less prolonged cold weather.

Beyond atmospheric factors, ocean conditions also played a key role. According to Dr. Kien, this winter, ENSO (a natural climate oscillation significantly impacting weather and climate in many regions) was in a weak La Nina state and trending towards neutral. This state created atmospheric circulation unfavorable for strong, prolonged cold air spells in the region.

Frost in Ta Xua in 2025. Photo: Xuan Hoa

Additionally, sea surface temperatures in the West Pacific and the South China Sea were about 0,5-1,5 degrees Celsius higher than the multi-year average. As cold air masses from continental Asia moved southward and passed over these warm waters, they rapidly weakened. "Therefore, when cold spells reached northern Vietnam, their intensity had often decreased significantly, and the cold weather did not last long," Mr. Kien stated.

Climate scientists note that climate change trends are also contributing to altering winter characteristics in many parts of the world. As average atmospheric and ocean temperatures rise, prolonged cold winters tend to diminish.

2026 forecast to be hotter, longer

According to Mr. Nguyen Van Huong, Head of the Weather Forecasting Department at the National Center for Hydro-Meteorological Forecasting, large-scale climate factors in 2026 are experiencing many fluctuations.

The ENSO phenomenon is currently in a weak La Nina state, with sea surface temperature anomalies in the central Pacific region around minus 0,6 degrees at the end of 2/2026. However, forecast models suggest that over the next three months, ENSO has a high probability (80-90%) of gradually transitioning to a neutral state; the probability of La Nina persisting decreased to about 10-20%.

From June to August 2026, ENSO is likely to remain neutral but will gradually lean towards the warm phase, with a 35-45% chance of transitioning to El Nino. This warming trend could become more pronounced from early autumn 2026 and potentially shift to El Nino by late 2026, early 2027.

Amidst global temperatures continuing at record high levels, the World Meteorological Organization warns that 2026 will likely remain among the hottest years ever recorded.

Heatwave in Hanoi 6/2025. Photo: Giang Huy

For Vietnam, the ENSO phase shift combined with the impacts of climate change could lead to heatwaves in 2026 appearing earlier, lasting longer, and increasing in intensity compared to the multi-year average.

Forecasts indicate that in 3/2026, widespread heatwaves will continue in southeastern Vietnam, while northwestern Vietnam may experience localized heatwaves. In April, heatwaves will intensify and expand to the Central Highlands and southwestern Vietnam; from Thanh Hoa to Hue, heatwaves will begin to appear.

From late 5/2026, heatwaves are predicted to expand across northern and central Vietnam, with intensity sharply increasing and remaining at peak levels during June to August.

Regarding storm activity in the South China Sea, the period from 3/2026 to 7/2026 is forecast to be at a level comparable to the multi-year average. However, from August to year-end, the number of storms and tropical depressions may be lower than average.

Despite this, given high sea surface temperatures and an ENSO leaning towards warming, the risk of strong storms with rapid development and complex trajectories still requires special attention. Meteorological experts also warn that extreme weather phenomena such as thunderstorms, whirlwinds, lightning, and localized heavy rain may occur more frequently during the transitional seasons of 2026.

Gia Chinh