1991 WMHB Atlantic hurricane season

The 1991 Atlantic hurricane season was a near-average season. The hurricane season officially began on June 1st and ended on November 30th. The season was slightly below-average due to a weak early-season El Nino. The season's first storm, Tropical Storm Ana, developed on July 5th and churned in the open Atlantic without any effects on land. The season's last storm, Tropical Storm Juan, dissipated on November 4th.

By far the season's most notable storm was its first major hurricane, Hurricane Bob, a powerful and destructive tropical cyclone which caused $11 billion in damage (1991 USD) and 1,090 fatalities across the Caribbean islands and Central America. Bob was also the season's strongest storm with maximum sustained wind speeds of 140 mph (220 km/h) while north of Puerto Rico. Only one other major hurricane developed in 1991, Hurricane Henri, which briefly attained wind speeds of 115 mph (185 km/h).

Tropical Storm Ana
On July 3rd, a tropical wave exited the coast of Africa. Under marginally favorable conditions, the wave developed into the season's first tropical depression two days later. Conditions gradually became more favorable for development as the depression tracked westwards, and on July 6th it strengthened into Tropical Storm Ana. However, light wind shear hindered further strengthening of the storm, and Ana weakened back to a tropical depression at 2:00 UTC the next day.

On July 8th, strong wind shear, caused by a weak El Nino, became much more unfavorable for sustainment of a tropical storm, and Ana began to rapidly weaken shortly after restrengthening into a tropical storm. At 17:00 UTC, a reconnaissance flight into a weakening Ana confirmed that it had weakened into a disorganized tropical wave, and advisories were discontinued an hour later before Ana dissipated over the open Atlantic at 23:00 UTC the same day.

Hurricane Bob
After over a month of inactivity, conditions in the Atlantic basin became more favorable as the El Nino began to dissipate. On August 7th, Tropical Depression Two formed over the Atlantic Ocean from a strong and well-organized tropical wave. By 16:00 UTC that day, the tropical depression had strengthened into Tropical Storm Bob. Possessing a large wind field for a tropical storm, Bob began to steadily intensify under favorable conditions fueled by warm ocean waters, becoming the 1991 season's first hurricane on August 9th. Shortly after being upgraded to a hurricane, Bob began to rapidly intensify as it tracked west-southwest towards the Caribbean islands.

By August 10th, Bob had become a Category 3 major hurricane, increasing its wind speeds from 80 mph to 120 mph in just 20 hours. The storm's wind field had also grown large, possessing a hurricane-force wind field of 180 miles and a tropical storm-force wind field of 580 miles. Bob's wind field continued to expand as the hurricane reached Category 4 intensity early on August 11th, reaching peak intensity north of Puerto Rico at 5:00 UTC. Bob's tropical storm-force wind field had grown to a massive 625 miles in diameter as it made landfall on Hispaniola with wind speeds of 130 mph (215 km/h). Torrential rainfall triggered severe flooding and mudslides that took the lives of at least 597 people as well as causing $2.4 billion in damages, making Bob one of the worst natural disasters ever to strike the island. From there, Bob continued westward to strike Cuba on August 18th as a Category 3 hurricane, causing a further 142 fatalities and $3 billion in damages from flooding and landslides.

Bob continued to slowly track westwards towards the Yucatan Peninsula, making landfall in Belize on August 20th with wind speeds of 105 mph (165 km/h). The large size of the storm allowed heavy rainfall to cause deadly mudslides in Honduras and Guatemala, which caused 351 fatalities in total. Damage was very severe to Belize and Mexico, at $5.6 billion USD in damages estimated. Bob then began to rapidly weaken over the mountainous terrain of Central America, becoming a tropical storm as it briefly passed offshore into the Bay of Campeche. On August 24th, Bob finally dissipated over the Mexican state of Guerrero after persisting as a weak tropical depression for nearly 4 days. With an estimated $11 billion (1991 USD) in total damages, Bob was, at the time, the costliest Atlantic hurricane on record until it was surpassed by Hurricane Opal in 1995.

Retirement
In the spring of 1992, the World Meteorological Association retired the name Bob from the list above due to its devastating impacts in the Caribbean and Central America. It was replaced by Bill for the 1997 Atlantic hurricane season.