March is still early enough to catch the beginnings of a norther. The approach of a norther will begin with south to south west winds, shifting clockwise to the west, northwest and north over a period of from 12 to 36 hours or more. You watch the weather you'll see when one is approaching the keys. Kick out into the Atlantic when the winds start in the south and you can have a great sail east up the keys. They don't blow hard from the south and will shift pretty fast to the west and northwest but you can often have one last long enough to make Miami in an overnighter. Once they shift to the north/northeast and you've passed Marathon where the islands swing to the northeast you'll have to 'hang' somewhere until another front moves through. Marathon is/was a good anchorage to hold up in.

Night passages along these islands is pretty safe if you just watch your fathometer and stay outside the 10 fathom line...and watch for traffic.