By Marc Frank Reuters August 28, 2012 HAVANA, Aug 28 (Reuters) - The Cuban coffee harvest began ahead of schedule this week, with farmers scrambling to pick ripe beans over the weekend as tropical storm Isaac bore down on the island and then left a rapidly maturing crop in its wake. Isaac moved along the north coast of the eastern part of the country on Saturday, home to some 90 percent of the coffee crop, shaking plants and delivering torrential rains before heading toward the United States. "We picked mature beans as Isaac's winds blew around us, and now we have to move the harvest up because lots of coffee will ripen quickly," coffee farmer Adela Martinez said in a telephone interview from eastern Santiago de Cuba. Isaac left the crop maturing more rapidly than expected, but otherwise left it unscathed, other sources in the major producing provinces of Guantanamo, Santiago and Granma said. Losses suffered in the coffee-producing municipali...