By Stephanie Nebehay GENEVA (Reuters) - The European Union must quickly establish adequate centres to receive and register asylum seekers in Greece and Italy and then distribute them across the bloc before winter sets in, the United Nations said on Friday. More than 591,000 people have crossed the Mediterranean by sea this year, including 450,000 to Greece, and this week 85 boats have been arriving daily on the island of Lesbos, the U.N. High Commissioner for Refugees said. "We don't know the full reasons for this surge in arrivals: it could be the result of a temporary improvement in the weather, a rush to beat the onset of winter and a fear that European borders may soon close," UNHCR spokesman Adrian Edwards told a news briefing.