I notice that no-one has responded to this. I don't have specific experience on the coastal, but walked earlier in the year after some rain from Valenca, and last year on the Central from Lisbon. The only place that I can recall that would become impassable after rain would be the complementary route leading into Pontevedra. The path is quite close to the rio Gatos, and even when I walked there was evidence of recent flooding that would have closed this complementary path.
As a general observation, I don't think any of the main routes will become impassable, albeit where there are unsealed surfaces, some might become quite muddy and difficult. There were places where there was evidence that his had happened in the past, with the trail being widened in such places as people attempted to find ways around where water might have collected across the path.
This is always a hard call. While one might be tempted to go around such obstacles, much less disruption is caused by walking through them, and not spreading the path. I wish I could say I have been consistent in applying this practice, but I cannot. There are times when I have tested the depth of the pooled water and it has well exceeded that which would have flooded my boots, and I have found a shallower way around.
