The rainy season in HCM City and southern Vietnam could end 15-20 days earlier than usual, while El Nino is forecast to remain strong in late 2026.
Meteorologists warn that the combination could bring an unusually harsh dry season, with earlier heatwaves, declining rainfall and increased drought risks.
According to Ngo Nam Thinh, head of the Meteorology and Climate Change Department at HCM City University of Natural Resources and Environment, El Nino was reducing moisture reaching Southeast Asia, while a weakening southwest monsoon and high-pressure systems were limiting rainfall across southern Vietnam.
Thinh added that the rainy season, which normally ends in late November or early December, could finish 15-20 days earlier this year, reducing natural water replenishment.
Experimental forecasts suggest November rainfall at Tan Son Hoa and Vung Tau monitoring stations could be 7-14 per cent below the 2010-2024 average.
However, the National Centre for Hydro-Meteorological Forecasting expects November rainfall across southern Vietnam to remain near normal, with temperatures 0.5-1 degree Celsius above average.
Despite declining rainfall, the seasonal transition could still bring severe thunderstorms, lightning, hail and strong winds. Tropical weather systems over the southern East Sea may also trigger unseasonal rain.
Pham Thi Thanh Nga, director of the Institute of Meteorology, Hydrology, Environment and Marine Science, said rising global temperatures could intensify the impacts of El Nino and La Nina.
El Nino could remain strong into 2027, increasing the risks of reduced rainfall, declining river flows and water shortages.
Heatwaves and water shortages pose growing risks
Thinh warned that an early end to the rainy season, combined with El Nino, could increase drought risks across HCM City and southern Vietnam in 2026-2027.
Lower rainfall would reduce surface water and groundwater supplies, while higher temperatures would accelerate evaporation.
Seasonal forecasts indicate temperatures between February and April 2027 could be 1-2 degrees Celsius above normal, with some areas experiencing greater increases.
In southeastern Vietnam, hot weather could begin in February, earlier than usual, and intensify during March and April.
Experts warned that HCM City's urban heat island effect could worsen conditions, with temperatures in central areas potentially 2-4 degrees Celsius higher than in surrounding districts.
Nguyen Van Hong, deputy director of the southern branch of the Institute of Meteorology, Hydrology, Environment and Marine Science, warned that extreme heat threatened outdoor workers, children, older people and those with underlying conditions.
Declining upstream river levels, combined with high tides, could also increase saltwater intrusion into the Tien, Hau, Saigon and Vam Co rivers, threatening agriculture and domestic water supplies.
River flows across much of the Dong Nai River basin were 8.4-50 per cent below average between July and September 2026.
HCM City has instructed relevant agencies to increase water storage ahead of the 2027 dry season.
Thinh recommended closer monitoring of Mekong River flows, saltwater intrusion and water reserves at major reservoirs, including Tri An, Dau Tieng and Phuoc Hoa.
Local authorities were also urged to inspect irrigation systems, embankments and saltwater barriers to improve freshwater storage.
Experts advised residents and businesses to conserve water, prepare emergency supplies and limit outdoor activities during extreme heat.
They stressed that early preparations would be essential to reducing the impacts of drought, heatwaves and saltwater intrusion during the coming dry season.