Tran Van Hung, deputy director of the Southern Regional Hydro-Meteorological Centre, said the rainy season typically begins between May 10 and 20, but could arrive sooner this year due to the southwest monsoon.
Transitional rains are often accompanied by lightning, squalls and even hail, he warned, urging residents to take precautions.
Last year, the city recorded its heaviest early-season downpour in eight years on May 10, with nearly 230 mm of rain in about 90 minutes, causing widespread flooding in low-lying areas.
In recent days, the southern region of Vietnam has endured intense heat as a western low-pressure system expanded, with temperatures reaching 37-38 degrees Celsius in areas such as Hoc Mon, Cu Chi and Go Vap, as well as nearby Binh Duong Province.
Forecasters said there is a 50-70 per cent chance of thunderstorms in central HCM City and outlying districts, including Hoc Mon and Binh Chanh, on April 29-30. Short bursts of rain on already hot days could make conditions feel even more humid and oppressive.