The finding may help explain what has been described as a “hurricane drought” in recent years, in which, despite greater hurricane activity, fewer destructive storms have hit the Eastern United States. Some scientists think the Atlantic may now be entering a quieter period, which could result in more of the stronger storms making landfall.

It is unclear what impact global warming and the continuing rise in ocean temperatures may have on the trend.

Scientists say a long-term pattern of climate variability called the Atlantic meridional mode helps determine the level of hurricane activity. In one phase, the mode results in warmer surface water in the tropical Atlantic and less wind shear, or changes in wind speed with altitude. Both circumstances favor the formation of hurricanes.

But at the same time, conditions near the coastal United States are the opposite: colder water, which provides less energy to a hurricane, and more wind shear, which tends to rip a storm apart. So although more hurricanes may form in the open ocean, as they approach land they are more likely to weaken. This protective barrier, as Dr. Kossin called it, does not exist in the Caribbean.

In a period of less hurricane activity, the mode shifts and opposite conditions prevail, both in the ocean and along the coast. That means fewer hurricanes but a greater likelihood of their intensifying near the United States.