Why have thunder, lightning been so frequent in Ho Chi Minh City?

The phenomenon is linked to the unstable atmospheric conditions prevailing over southern Vietnam, said Le Dinh Quyet, head of the forecasting division at the Southern Regional Hydro-Meteorological Center.

From late morning through midday and into the early afternoon, relatively clear skies and strong sunshine heating the ground have caused temperatures to rise and created hot, humid conditions.

By afternoon, easterly winds carry moisture from the sea inland, where it encounters the high temperatures near the surface.

The contrasting air masses cause strong atmospheric mixing and instability, while the potential energy available for convection reaches high levels.

When the atmosphere becomes highly unstable, towering convective clouds can develop.

Under these conditions, electrical charges in the clouds and on the ground can interact, with opposite charges attracting one another and triggering repeated lightning and thunder.

Weather expert Le Thi Xuan Lan said September and October are typically the wettest period of the rainy season in southern Vietnam.

During the period, the region is mainly influenced by the southwest monsoon combined with the intertropical convergence zone, whose axis generally extends from west-northwest to east-southeast across central Vietnam before shifting southward over the southern region.

Tropical storms or depressions can also develop within the convergence zone during September and October, making these two months the peak of the rainy season.

On average, southern Vietnam experiences rain on 15 to 20 days each month during this period, with at least five to seven days bringing heavy rainfall.

Lan noted that Ho Chi Minh City had recently experienced an unusual pattern, with rain battering the city at night and in the morning before becoming particularly heavy from afternoon into evening.

Rainfall totals in many areas reached 50 to more than 100 millimeters, while some locations recorded more than 150 millimeters in a single day.

She attributed the recent spell to a low-pressure area and atmospheric disturbance that developed from September 30 through October 1 as easterly and southwesterly winds converged.

This phenomenon, sometimes referred to as an easterly wave disturbance, moved inland from the sea.

With this type of weather system, rain can begin at any time of day or night, depending on when the disturbance reaches the mainland.

Rain continues as the disturbance moves westward, weakens and eventually dissipates.

Although the low-pressure area was not as powerful as a tropical depression or typhoon, it transported a substantial amount of moisture-laden clouds from the sea toward the mainland, fueling widespread rainfall.

Dense thunderstorm clouds have covered much of southern Vietnam, particularly Ho Chi Minh City.

Lan said the city’s urbanization and resulting urban heat-island effect further contribute to the development of thunderstorms.

Within the convergence zone, convective clouds are able to grow to heights of around 6 to 10 kilometers, creating favorable conditions for the frequent thunder and lightning.

The city was hit by heavy rain, preceded and accompanied by almost continuous thunder and lightning on the night of September 29 and into the early hours of September 30.

Several lightning strikes illuminated the urban skyline in the middle of the night, waking residents from their sleep.

Heavy rain continued on the afternoon of September 30, when a resident captured an image of lightning striking a house during the downpour.

On Thursday afternoon, another powerful thunderstorm swept across Ho Chi Minh City, bringing repeated flashes of lightning and prolonged rumbling thunder throughout the heavy rain.