WeatherWhys for November 18,2015 from accuweather.com

Hurricane Lenny spent its entire lifespan traveling in a west-to-east fashion from the central Caribbean to the Atlantic, which was unprecedented in the history of tropical record keeping. Tropical systems are typically guided westward from the Atlantic to the Caribbean by high pressure, then may curve to the northeast if they encounter a dip in the jet stream over North America. In Lenny's case, a large dip in the jet stream was in place over the western Atlantic and put the hurricane on its eastward track.