The North to South mantra is said so often that it must be true. The funny thing is that when I rode the Pacific Coast (N-S) there wasn't all that much wind. Yes there were a few tail winds, but nothing like I was expecting. There were also days with headwinds. I am not sure if it was just an anomaly or if it was because I tended to start out at the crack of dawn and finish very early in the afternoon. Perhaps I was just lucky or the winds didn't kick up until afternoon when I was in camp.
The time of day probably did have something to do with it. I have ridden N-S three times and tailwinds predominated, becoming significantly more pronounced in the afternoon as inland areas heat up and draw more ocean air. I felt sorry for northbound riders on a number of occasions!
Of course, nothing is for certain. Last year I departed San Francisco on June 4. Now, it almost never rains there in June, and if it does it's just a sprinkle. Not last year! A freak storm rolled in. Not only were there a couple hours of torrential rain, but the rest of the day down the coast was into the teeth of a direct head-on gale. At one point I passed a sign saying "Santa Cruz, 33 mi". TWO HOURS LATER I passed another sign "Santa Cruz, 25 mi" This was on mostly flat ground; the wind was just that intense.
But yes, generally you will get a tailwind , and a couple of days later things were back to normal.