​Brunei Darussalam will be transitioning from the inter-monsoon phase to the Southwest Monsoon, which is expected to begin in June 2025 and typically persists until September. During this period, atmospheric conditions tend to be more stable, resulting in fewer occurrences of thunderstorms compared to the inter-monsoon season. Winds are generally expected to blow from the southwest direction.

Southwest monsoon is also associated with the season of active development of tropical storms and typhoon systems over the Northwest Pacific Ocean and the South China Sea. Although these systems typically develop far from the region, their proximity and intensity still have the potential to influence local weather conditions in the country. The influence of tropical storm or typhoon systems nearby our region may lead to the formation of squall lines—fast-moving bands of thunderstorms arranged in a long, narrow line formation. This can bring unsettled weather conditions, including gusty winds and occasional thunderstorms.