LONDON (Reuters) - A higher-than-usual number of hurricanes are expected to slam into the United States this year, a leading hurricane forecaster said on Monday, threatening areas trying to rebuild from last year's devastating storms.

Tropical Storm Risk, a London-based storm forecaster, raised its outlook for hurricane activity in the Atlantic this year by 30 percent from its July outlook on the expectation of higher-than-normal sea temperatures and winds in the region.

There is a high probability of an above-average number of tropical storms, which can intensify into hurricanes, making landfall in the United State, the group said.