Mmmm, I've been snuck up on by the weather multiple times:

1) Dark, full moon, we're becalmed, we had very little/no warning of the approaching storm.

2) Cold front hit, no leading edge frontal clouds (very rare). Gusts to 30kts. Major capsize event.

In the above case, it appears they still had the spinnaker up and were attempting to out-run the storm...certainly dropping the main would have been a smart choice if you can get it to release on the water.

The beauty of some of these fast moving storms in more protected waters is they often approach with no fetch and the water remains flat. I've only experienced that once but 25-30 kts in dead flat water is extremely fast, and I quickly realized how the speed trenches work.