1991 Atlantic hurricane season

A season steered away from the tropics

Richard Pasch and Lixion Avila of the National Hurricane Center called 1991 a quiet year after three busy ones. Their count of eight tropical storms and four hurricanes, plus four depressions that never reached storm strength, fell below the long-term averages of about ten and six. The site's archive gives the same 8 tropical storms and 4 hurricanes, with accumulated cyclone energy of just 35.5. Best-track tallies that round the figure to 36 also include periods when storms were subtropical.

Upper-level westerlies explain most of that shortfall. From August to October, vertical shear ran stronger than normal over the Caribbean east of 80°W and the tropical Atlantic east of the Lesser Antilles, and weaker than normal across a subtropical belt where Bob, Claudette and Erika formed. No system reached hurricane strength south of 25°N, and no tropical storm entered the Gulf of Mexico, which the NHC noted had happened only in 1927 and 1962 earlier that century.

The NHC found no Cape Verde hurricanes that year. Only Danny, Erika and Fabian grew from African waves, and none of them became hurricanes. The area several hundred kilometers southwest to southeast of Bermuda served as the season's hot spot, where nontropical seedlings produced all four hurricanes.

Ana, a Mexican depression and a slow summer

Tropical Storm Ana formed about 160 km south of Charleston, South Carolina, on 2 July from a low that had drifted across southern Florida. A NOAA buoy measured 8-minute winds of 17 m/s on 3 July, enough for the upgrade, and a ship estimated Ana's peak winds at 23 m/s the next day. It lost its tropical character over cold water southeast of Newfoundland on 5 July.

A depression in the western Gulf of Mexico came ashore near La Pesca, Tamaulipas, on 6 July without reaching storm strength. Rain reached 17.47 inches at Tamazunchale in San Luis Potosí. Two further depressions near Cape Verde in late August fizzled over cool water.

Hurricane Bob and New England

Bob grew from a disturbance near Bermuda and became a tropical depression 330 km east of Nassau at 00 UTC on 16 August. It became a hurricane late on 17 August, east of Daytona Beach, and turned north between the Atlantic ridge and a trough over the southeastern United States. Early on 19 August the eye passed 45 to 55 km east of Cape Hatteras, and aircraft measured 950 mb off Virginia, a Category 3 reading. The archive puts Bob's peak at 100 kt and 950 hPa.

Cooler water off the mid-Atlantic coast weakened the storm. The eye crossed Block Island at 1720 UTC and Newport, Rhode Island, near 1800 UTC on 19 August, when the NHC rated Bob a Category 2 hurricane with less than half an eyewall left. It made a final landfall as a tropical storm near Rockland, Maine, early on 20 August and became extratropical over the Gulf of St. Lawrence later that day.

The NHC associated 17 deaths with Bob: one each in South and North Carolina, two in New York, six in Connecticut, two in New Hampshire, three in Maine and two in Nova Scotia. Insured damage in the United States came to a preliminary $782 million, $525 million of it in Massachusetts. With flood claims, uninsured losses and cleanup, the NHC estimated total US damage at $1.5 billion in 1991 dollars. A surge of 2 m reached the Providence hurricane barrier, and about 2.1 million homes and businesses lost power. The WMO retired the name Bob.

Claudette's brief Category 4 peak

Claudette formed about 925 km southeast of Bermuda from a nontropical upper-level disturbance on 4 September. A large anticyclone overhead gave it efficient outflow, and it deepened faster than normal. The first reconnaissance flight late on 6 September found a compact hurricane with an 11 km eye and hurricane-force winds reaching only about 37 km from the center. Satellite estimates put the peak near 10 UTC on 7 September at 944 mb, a Category 4 storm; the archive records 115 kt. A NOAA research plane measured 959 mb six hours later.

Hurricane warnings went up briefly for Bermuda, but Claudette passed about 205 km east-southeast of the island late on 8 September, and sustained winds there reached only about 10 m/s. Tropical Storm Erika formed on 9 September midway between Claudette and Tropical Storm Danny, interacted briefly with Claudette and raced to the Azores, where Santa Maria recorded a 30 m/s gust and closed its airfield for several hours. Danny opened up into a tropical wave east of the Lesser Antilles on 11 September.

Fabian, Grace and the Perfect Storm

Tropical Storm Fabian formed south of the Isle of Youth on 15 October and crossed western Cuba. The NHC recorded 157 mm of rain at Caonao, near Cienfuegos, and received no reports of casualties or damage. Hurricane Grace began as a subtropical storm south of Bermuda on 26 October, became tropical on 27 October and reached its peak of 46 m/s, about 90 kt, on 29 October as a strengthening extratropical low to the north flung it eastward. The center passed about 85 km south of Bermuda, which saw only light winds from Grace itself.

That extratropical low became the storm later known as the Perfect Storm. The NHC reported a peak of about 972 mb and 40 m/s south of Halifax on 30 October, with wave heights of 30.8 m at a Canadian buoy. Waves and tidal flooding damaged coasts from the Greater Antilles to Canada. The storm caused more than $200 million in damage in 1991 dollars and 13 deaths, most while the storm was extratropical, including the six crew of the Andrea Gail.

Over Gulf Stream water near 26°C, a tropical cyclone formed inside the decaying low on 1 November and reached hurricane strength, 65 kt in the archive. It crossed the coast near Halifax as a weakening tropical storm on 2 November. The NHC left it unnamed: forecasters feared a name would confuse the media and public while attention stayed on damage from the earlier extratropical storm, so warnings went out through marine forecasts. The archive still counts it among the season's 4 hurricanes.