According to this study by the UK Met Office there is a positive correlation between air temperature and precipitation in the winter and a negative correlation in the summer. That is to say, in winter, as the temperature rises, precipitation increases, but in summer the reverse occurs.
Another way of looking at it is to say that, on average, rain usually falls in a fairly narrow range of temperatures: cooler in the summer, warmer in the winter. This partly explains why FurTech type clothing can be worn in the rain throughout the year.
If it's warm and not raining then there's no reason to be wearing it!
That said, my worst experience of wearing this type of kit was in hot, humid conditions on the Tour De Mont Blanc in 1997, wearing salopettes and jacket. There wasn't a breath of wind. In these "tropical" conditions it may be better just to wear shorts and dry off later - skin dries far faster than clothing. (I don't believe I would have been any more comfortable in any other clothing system for the reasons explained on this link.)