Why is northern Vietnam still unusually hot in late October?

Dozens of historical temperature highs recorded in October

In the final days of October, when northern Vietnam normally begins to feel the chill of autumn more distinctly, Hanoi has continued to experience strong sunshine and uncomfortable heat during the day. Maximum temperatures in Hanoi and many other northern localities have generally ranged from 30°C to 33°C, exceeding 34°C in some places.

The unusually high temperatures have not been confined to the final days of the month. Statistics show the country recorded 59 instances in which daily maximum temperatures equalled or exceeded historical highs during the first 20 days of October.

At Lang meteorological station in Hanoi, the temperature reached 37.1°C on October 2, surpassing the previous high of 36.4°C recorded on October 5, 2023. Yen Chau station in northern Son La province recorded 38.3°C on October 3, exceeding the previous benchmark of 37.5°C set on October 23, 2019. On the same day, Hon Dau station in Hai Phong recorded 37.2°C, well above the 34.8°C observed on the corresponding date in 2014.

The unusually high temperatures are not limited to the north. Several localities in central and southern Vietnam also saw daily maximum temperatures match or exceed previous historical highs. Tuyen Hoa station in Quang Tri province reached 37°C on October 4, while Bien Hoa station in Dong Nai province recorded 36.2°C on October 1.

These figures point to multiple episodes of unusually high temperatures across the country during the seasonal transition. However, the number of times temperatures at monitoring stations matched or exceeded historical benchmarks should not be confused with the number of hot days or the number of localities experiencing unprecedented heat. A comprehensive assessment of the month's conditions requires monthly mean temperature data to be compared with long-term observations.

Strong El Niño and weather patterns contribute to persistent heat

Explaining why northern Vietnam remains hot towards the end of autumn, Nguyen Hong Sinh, deputy director of the Hai Phong Hydrometeorological Station, said the high temperatures are linked to climate change, global warming and the exceptionally strong El Niño phenomenon.

According to meteorological updates published in October, sea surface temperatures in the central-eastern equatorial Pacific, particularly the Niño 3.4 monitoring region, were 2.1°C above the long-term average in September, rising to 2.4°C in mid-October. These conditions indicate that El Niño is intensifying and could have a significant impact on temperatures and rainfall patterns in Vietnam.

But El Niño is not the only factor determining daily temperatures in northern Vietnam. Actual conditions also depend on weather systems affecting the region, particularly the subtropical high-pressure system aloft and incoming cold-air masses.

Nguyen Duc Hoa, deputy head of the Climate Forecasting Division at the National Centre for Hydro-Meteorological Forecasting, said it was the first time since 1991 that a widespread heatwave had been recorded across the entire northern region in October.

Hoa identified three broad factors contributing to the unusually hot autumn - climate change, El Niño and short-term weather patterns. During the early October heatwave, the southern flank of a low-pressure trough, combined with the circulation of the subtropical high-pressure system aloft, helped sustain widespread heat and pushed temperatures at several monitoring stations to or above previous highs for the corresponding period.

Cold-air surges have also not been strong enough, or have not persisted long enough, to bring about a sustained drop in temperatures. When their influence weakens, skies can quickly become clearer and sunshine more prevalent, allowing daytime temperatures to rise again.

This helps explain why people continue to experience uncomfortable heat even as October draws to a close. Yet, high temperatures should be distinguished from a meteorologically defined heatwave - temperatures exceeding 30°C do not automatically qualify a day as a heatwave under meteorological criteria.

Will winter be warmer than usual?

October's unusual weather has also raised questions about conditions in the coming months, as northern Vietnam prepares to enter winter.

According to the National Centre for Hydro-Meteorological Forecasting, the country's average temperature in October is forecast to be 0.5–1.5°C above the long-term average, with larger deviations in some places. In its seasonal outlook covering October 2026 to March 2027, the centre forecast that average temperatures nationwide in October–November 2026 and February–March 2027 would generally be 1–2°C above the long-term average.

For December 2026 and January 2027, average temperatures in many areas are forecast to be 0.5–1.5°C above the long-term average. The meteorological agency also expects cold-air activity during the winter to be weaker than usual, potentially resulting in fewer days of severe and extreme cold in northern Vietnam and the north-central region.

Nevertheless, a higher seasonal average does not mean winter will be entirely free of severe cold spells. Strong cold-air surges may still occur, causing temperatures to plunge for short periods.

In the longer term, unusual heat episodes need to be considered in the context of both climate change and natural climate variability, including El Niño. A single hot spell is not sufficient to establish climate change as its direct cause. Long-term observations and trends in temperature extremes, however, are important evidence for assessing broader changes in the climate.

October 2026 illustrates how the seasonal transition in northern Vietnam can depart significantly from historical patterns. Continued monitoring of official observations and updates from meteorological authorities will be essential to assess the month’s overall temperature anomalies and better understand weather trends towards the end of the year.

Cold air mass to ease heat in the north, temperatures fall to 19–22°C

VOV.VN - Northern Vietnam is still seeing temperatures of up to 34–35°C, but a cold air mass is forecast to move in from the evening of October 4, bringing rain and a marked drop in temperatures, with lows of 19–22°C expected in the region during the cold spell.