Air quality across Singapore turned unhealthy overnight as the haze settling over the island thickened. The National Environment Agency said showers are forecast for Saturday over Singapore and the surrounding region. Rainfall could knock some of the polluting particles out of the air, but the agency warned that smoke haze might keep drifting in from Sumatra. Fires on the Indonesian island are the usual source of the smoke that reaches Singapore during dry periods of the year. Readings in the unhealthy band generally prompt advisories for people to cut back on strenuous outdoor activity. Residents will be watching the sky over the weekend, since wind patterns will decide whether the episode eases or lingers. Updated air quality figures are expected from the agency as conditions change.