The weather in the tropics is always a gamble. At some places, you can set your clock by the rains during monsoon season. If it's 3:45pm, you're about to get soaked. At others, you only know that at some point during the afternoon, a lot of rain is going to fall. It might rain at 1pm. Or it might rain at 5pm. But of one thing you can be certain: a hard rain is gonna fall, and it will flood the track.
Friday at Sepang the rain came shortly after 2:15pm, less than a quarter of the way through the Moto2 FP2 session. Light at first, then more heavily, then a torrent of water from the heavens, forcing a red flag, and a delay of an hour.
It caught everyone by surprise. The forecast had been for dry weather through the afternoon, and teams had made their plans accordingly. That meant that in FP1, a lot of riders didn't bother putting in a set of soft tires to chase a fast lap, expecting to improve in the afternoon.