Hong Kong was hit by its first black rainstorm warning of the year on Monday evening, as intense downpours and thunderstorms swept across the city.

The Hong Kong Observatory issued the black rainstorm warning at 8:35 pm, and it remained in force for one hour until 9:35 pm. All rainstorm warning signals were canceled by 10:45 pm, although the observatory said weather conditions remain unstable with heavy rain likely to continue.

A black rainstorm warning, the highest in the three-tier system, is issued when more than 70 millimeters of rainfall is expected in an hour.

The warning came after an abrupt amber rainstorm warning on Saturday morning, followed by a red warning that same afternoon. Unsettled weather persisted through the weekend and into Monday, with rainstorm signals issued on and off.

According to the observatory, an active southwesterly airstream and a trough of low pressure brought cloudy weather, heavy showers and squally thunderstorms to the Guangdong coast.

The observatory said heavy showers and thunderstorms are likely to continue on Tuesday before easing gradually around midweek.