I would expect some correlation with the weather: nicer weather means nicer tube trips because, with worse weather, more people take the tube, and they will wear thicker, wetter clothes. Also, if it is extremely hot, the tube can be relatively cool (depends heavily on the tube in question)
The tube also can be extremely busy (sometimes with very noisy passengers) due to sales in shopping centers or due to sporting matches, exhibitions, etc.
The tube also can be extremely busy (sometimes with very noisy passengers) due to sales in shopping centers or due to sporting matches, exhibitions, etc.