According to Vietnam’s Department of Hydrometeorology, as of Sept. 7, a mass of cold air over China was moving toward Vietnam and is forecast to affect northern provinces between Sept. 9 and 11.

It is expected to be the first cold air mass to affect Vietnam during the 2026-2027 winter season, although its intensity is not forecast to be particularly strong.

Under the influence of the cold air, northern provinces could see rain and showers from the night of Sept. 9 into Sept. 10, with moderate to heavy rain and thunderstorms in some areas. Rainfall is then expected to ease quickly.

Notably, temperatures across northern Vietnam are forecast to decline from Sept. 10-12, with daytime highs falling below 33 degrees Celsius and nighttime and early-morning lows dropping below 25 degrees. In the northern midlands and mountainous areas, minimum temperatures could fall below 23 degrees.

Historical data show that the season’s first cold spell typically arrives between Sept. 12 and Oct. 4. The earliest on record occurred on Aug. 16, 2003.

If this cold air mass begins affecting northern Vietnam around Sept. 9-10 as forecast, its arrival would be roughly three to five days earlier than the long-term average.

East Sea could see tropical depression or storm

As the cold air strengthens, another notable weather system is expected to develop over the East Sea.

From Sept. 9, an intertropical convergence zone is forecast to form over the East Sea, with its axis extending across Vietnam’s central region.

A tropical depression has a high probability of developing over the central East Sea around Sept. 12-13, with the likelihood estimated at 70-80%. It could subsequently strengthen into a storm, with a probability of around 30-40%.

The weather agency stressed that these remain forecast scenarios. The tropical depression’s development and its potential intensification into a storm will need to be closely monitored and forecasts updated over the coming days.

Central Vietnam faces risk of widespread heavy rain

If a tropical depression or storm develops, its interaction with the cold air mass and intertropical convergence zone could bring a widespread spell of moderate to heavy rain to central Vietnam between Sept. 10 and 17, according to the weather agency.

The rainfall could also bring a high risk of dangerous weather, including tornadoes, lightning, flash floods, landslides and localized flooding.

Based on current forecasts, meteorologists have outlined two main scenarios.

Scenario 1, with an estimated probability of 60-70%, would see heavy rain begin in central Vietnam on Sept. 10 and continue through Sept. 16. The heaviest rainfall would likely be concentrated from Ha Tinh to Gia Lai.

Scenario 2, with a probability of around 30-40%, would see heavy rain begin around Sept. 14 and last until Sept. 17, with the main rainfall zone extending from Nghe An to Hue.

In addition, the southwest monsoon is expected to strengthen between Sept. 9 and 12, bringing more frequent thunderstorms to Vietnam’s Central Highlands and southern regions.

The Department of Hydrometeorology has called on ministries, government agencies and local authorities to proactively prepare response plans to protect lives and property.

Bao Anh