Hurricane Bob was one of the costliest hurricanes in New England history. The second named storm and first hurricane of the 1991 Atlantic hurricane season, Bob developed from an area of low pressure near The Bahamas on August 16. The depression steadily intensified, and became Tropical Storm Bob late on August 16. Bob curved north-northwestward as a tropical storm, but re-curved to the north-northeast after becoming a hurricane on August 17. As such, it brushed the Outer Banks of North Carolina on August 18 and August 19, and subsequently intensified into a major hurricane. After peaking in intensity with maximum sustained winds of 115 mph (185 km/h), Bob weakened slightly as it approached the coast of New England.

The 1991 Atlantic hurricane season was the first season since 1984 in which no hurricanes developed from tropical waves, which are the source for most North Atlantic tropical cyclones. The hurricane season officially began on June 1, and ended on November 30. It was the least active in four years due to higher than usual wind shear across the Atlantic Ocean. The first storm, Ana, developed on July 2 off the southeast United States and dissipated without causing significant effects. Two other tropical storms in the season – Danny and Erika – did not significantly affect land. Danny dissipated east of the Lesser Antilles, and Erika passed through the Azores before becoming extratropical. In addition, there were four non-developing tropical depressions. The second depression of the season struck Mexico with significant accompanying rains.