Hurricane Irene is not a hurricane any more: it was demoted to a tropical storm after its sustained winds fell below 74 mph to an average of 55 mph, the National Hurricane Center said Sunday.

The center downgraded Irene shortly after 9 am but warned that it still poses serious threats to the greater New York City area, Long Island as well as parts of New Jersey and Connecticut.

Despite the downgrade, challenges -- and dangers -- remained. New York City Mayor Michael Bloomberg said the storm surge lapping the promenade of Battery Park City was causing authorities to consider cutting power to lower Manhattan, home to international stock, futures and commodity exchanges as well as numerous brokerage firms and hedge funds.

Consolidated Edison Co. said sluch an action would affect up to 6,500 people.

Meanwhile, about 9,600 residents in New York City remained Sunday morning in shelters and the mayor urged residents to remain indoors out of concern for flying debris and the possibility of live power lines falling down.