Vietnam to see high chance of neutral ENSO conditions through June-November

The national weather agency said on Thursday that sea surface temperatures in the central equatorial Pacific were near average in early May, indicating ENSO is currently in a neutral phase.

The probability of neutral conditions continuing through November ranges from 55 percent to 90 percent.

Heat, rainfall outlook

Between June and August, heatwaves are forecast to persist in northern and central Vietnam, while easing in the Central Highlands and southern regions.

The intensity of this year's heat is expected to be on par with the long-term average, though northwestern Vietnam may experience temperatures 0.5 to 1 degree Celsius higher than usual.

Moderate to heavy rainfall is possible across many regions, particularly the north, north-central provinces, Central Highlands, and the south.

Rainfall totals are projected to match historical averages, though levels could be 5-20 percent higher in southern Vietnam, along with the south-central provinces of Ninh Thuan and Binh Thuan.

Severe weather events such as thunderstorms, lightning, hail, and strong winds may also occur during this period.

From September to November, heatwaves will possibly become localized in the north and central regions during September before ceasing.

Widespread rainfall is expected to increase, especially in central Vietnam, where authorities warn of heightened risks of flash floods, landslides, and urban inundation.

Storms, tropical depressions

The number of storms and tropical depressions forming in the East Vietnam Sea and impacting Vietnam is forecast to be close to the long-term average—typically 11 systems, with about five making landfall.

Between now and August, around 5.2 storms or depressions could form over the East Vietnam Sea, with two possibly hitting mainland Vietnam.

Flood risks

In northern Vietnam, 3-4 flood events are anticipated, with water levels on major rivers reaching alarm levels 1-2, and small rivers potentially exceeding level 3.

North-central provinces may see 1-3 minor floods, with water flows in Nghe An and Ha Tinh down by 25-60 percent. Conditions may improve in November.

In central Vietnam, many rivers will face water shortages of 40-75 percent. However, rivers such as Ta Trach, Thu Bon, and Tra Khuc could exceed 50 percent of the seasonal norm. 

From September to November, large floods above alarm level 3 are possible.

The Central Highlands may face 1-3 flood events, with its northern part experiencing flow deficits of up to 75 percent, while the southern areas may reach or exceed seasonal norms by 7-45 percent.

In southern Vietnam, the Dong Nai River could experience around three flood events.

The Mekong River is expected to enter the flood season from June or July.

Peak flooding in the lower Mekong is forecast for October to November, possibly exceeding level 3, while upper river areas will remain near alarm level 1.

What is ENSO?

ENSO, or El Niño-Southern Oscillation, refers to fluctuations between El Niño and La Niña phases.

El Niño years typically bring prolonged heat and drought, delayed rainy seasons, reduced flood, and storm activity.

In contrast, La Niña events are associated with strong and persistent monsoon winds, abundant rainfall, and more frequent storms and tropical depressions.