Think about that for a moment. What it suggests is that if things are going a bit too smoothly or calmly, WATCH OUT.... The storm is about to emerge. Many of us have experienced that, especially those of us who seem to go through periods in our lives when everything seems to be going wrong - one thing after the other.
When things are going too well, someone might say, "Just waiting for the storm to hit -- it always does!" And...sure enough, if we wait long enough, everything goes south.