Data from the National Centre for Hydro-Meteorological Forecasting shows northern Vietnam experienced about 13 cold spells from early winter to the end of February, but most were weak and short-lived.
As a result, average temperatures remained higher than usual. During the core winter months from December 2025 to February 2026, temperatures in many areas were about 0.1-2 degrees Celsius above the long-term average.
Nguyen Van Huong, head of weather forecasting at the centre, said the ENSO climate system is currently in a weak La Nina phase, with sea surface temperature anomalies in the central Pacific around minus 0.6 degrees Celsius at the end of February.
Climate models indicate an 80-90 per cent chance that ENSO will shift to a neutral phase within the next three months, reducing the likelihood of La Nina to around 10-20 per cent.
From June to August, ENSO is expected to remain neutral but show signs of warming, with a 35-45 per cent probability of developing into El Nino.
The warming signal could become clearer from early autumn, with a possible transition to El Nino by late 2026 or early 2027.
According to meteorologists, the shift in ENSO combined with climate change could cause heatwaves in Vietnam to begin earlier, last longer and become more intense compared with the long-term average.
Heat is expected to continue affecting southeastern Vietnam widely in March, while the northwestern region may experience localised hot spells.
By April, heatwaves are forecast to expand to the Central Highlands and the Mekong Delta, while areas from Thanh Hoa to Hue could begin experiencing the first hot periods.
From late May, heat is expected to spread across most of northern and central Vietnam, with peak temperatures likely between June and August.
Tropical storm activity in the East Sea between March and July is forecast to remain close to the long-term average, while the number of storms and tropical depressions from August to the end of the year may be slightly lower.
However, warmer sea surface temperatures and a warming ENSO trend could increase the risk of stronger storms with rapid development and more complex tracks.
Extreme weather events such as thunderstorms, whirlwinds, lightning and localised heavy rain are also expected to occur more frequently during seasonal transitions in 2026.
Truong Ba Kien, deputy director of the Climate Research Centre under the Institute of Meteorology, Hydrology and Climate Change, said this winter had been influenced by several large-scale climate factors.
