According to the Southern Regional Hydro-Meteorological Centre, temperatures on Friday ranged from 35 degrees Celsius to 36 degrees Celsius across much of the region, with some areas exceeding 36 degrees Celsius.
Several southern localities recorded temperatures above 37 degrees Celsius on May 14, including Tay Ninh at 37.5 degrees Celsius and Bien Hoa in Dong Nai Province at 37.3 degrees Celsius.
Forecasters said weather conditions would begin shifting late on May 15 as the southwest monsoon becomes established.
From May 16 onwards, rainfall and thunderstorms are expected to intensify, with some areas likely to experience heavy to very heavy rain.
Authorities warned of risks including lightning, whirlwinds and strong winds, while localised flooding could affect low-lying areas and disrupt traffic during peak hours.