Two storm systems expected to pound the Northeast with snow, ice and high winds failed to merge Wednesday, but flight delays and cancellations still piled up at some of the busiest airports as rain from Maine to the Carolinas soaked Americans trying to get home on the busiest travel day of the year. The snarls were expected to grow, and drivers in New York, Pennsylvania, Ohio and West Virginia faced treacherous icy roads. Large crowds waited for trains at Penn Station in New York on Tuesday night and New York’s three major airports were expecting 1.3 million fliers, about 30 percent more than an average Wednesday. Authorities there said that they were worried about strong wind later in the day. About 43 million Americans are expected to travel Wednesday with 3.1 million of them taking flights, according to AAA. In New York, organizers of the Macy’s Thanksgiving Day Parade kept an eye on the forecast for Thursday.