Keith will be posting the ‘official’ F1Fanatic weather forecast on Thursday, but until then:
At the moment the chance of rain is 30% for all three GP days according to meteoblue. Temperatures will exceed 30C every day. However, F1.com has also published their weather predictions: dry on Saturday and Sunday, but an evil looking thundercloud on Sunday.
From recent years: the trend in Malaysia has been that the morning is dry and heavy rain starts falling in the late afternoon, right when FP2, quali and the race will take place.