1991 Atlantic hurricane season

The 1991 Atlantic hurricane season was a below-average Atlantic hurricane season due to higher than usual wind shear across the Atlantic Ocean, which effectively stifled tropical cyclogenesis in the Main Development Region. There were 12 tropical cyclones this season, 8 of which became named storms. Among them, 4 become hurricanes, of which 2 became major hurricanes (Category 3 to 5 strength on the Saffir–Simpson scale). The season officially began on June 1, and ended on November 30.

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.

The most significant storm of the season was Hurricane Bob, which at the time was among the ten costliest United States hurricanes. After brushing the Outer Banks of North Carolina and Long Island in New York, the hurricane made landfall on Rhode Island. It caused $1.5 billion in damage (1991 USD), mostly in Massachusetts, and 17 fatalities. The strongest hurricane of the season was Claudette, which reached peak winds of near Bermuda. It passed near the island but did not cause any damage. Fabian was the only tropical storm to move over or near Cuba or Florida, producing heavy rainfall but no damage. Hurricane Grace, the final named storm of the season, provided the energy that led to the development of a powerful nor'easter known as the Perfect Storm. Originating from an extratropical storm, the Perfect Storm intensified while moving westward toward New England, leaving $200 million in damage and causing coastal damage from Puerto Rico to Florida and northward through Canada. It later transitioned into a hurricane over the Gulf Stream, finally dissipating over Nova Scotia on November 2.

Seasonal forecasts

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|+Predictions of tropical activity in the 1991 season

|- style="background:#CFCFCF; text-align:center;×÷≥"

|align="center"|Source

|align="center"|Date

|align="center"|Named storms

|align="center"|Hurricanes

|align="center"|Major hurricanes

|align="center"|Ref

|align="left"|CSU || April || <10 || <6 || Unknown ||

|align="left"|CSU || June || 8 || 4 || 1 || || 30 || 15 || 7 (Tie)

| style="text-align:center;" colspan="2"|Record low activity Later that month, the Weather Research Center forecast ten named storms and six hurricanes, of which five would become major hurricanes. while three would hit the United States. In early June, Gray released an updated report that predicted the formation of eight tropical storms, four hurricanes, and one major hurricane. The revised June total was very close to the actual season activity, with the exception of forecasting one fewer major hurricane.

Seasonal summary

For a chronological guide, see Timeline of the 1991 Atlantic hurricane season

Overall activity in 1991 was below normal. This was partially due to decreased tropical cyclogenesis from African tropical waves, which are troughs that move across the ocean with associated convection. In most seasons, the majority of storms develop from tropical waves. Of the season's twelve tropical cyclones, only five originated from tropical waves; in addition, only three of the eight tropical storms were from tropical waves, and none had the characteristics of a Cape Verde-type hurricane. From late April to late November, there were 73 tropical waves that exited the west coast of Africa. The total was higher than average, although many of them were poorly defined and had little thunderstorm activity. The waves traversed the Atlantic Ocean further south than normal, typically not becoming convectively active until moving across northern South America. Cyclogenesis was also suppressed by higher than normal wind shear, as well as low rainfall amounts across the Sahel. ACE is, broadly speaking, a measure of the power of the hurricane multiplied by the length of time it existed, so storms that last a long time, as well as particularly strong hurricanes, have high ACEs. ACE is only calculated for full advisories on tropical systems at or exceeding or tropical storm strength. Although officially, subtropical cyclones are excluded from the total, the figure above includes periods when storms were in a subtropical phase.

Systems

Tropical Storm Ana

The first storm of the season was Ana, which originated from a cold-core low that persisted east of Jacksonville, Florida, by June 25. The system moved in a clockwise motion around an anticyclone located over Florida. The cold-core low gradually developed to the surface, and on June 29, a low pressure area formed within a surface trough over the Bahamas. It moved westward across southern Florida, dropping heavy rainfall along its path. Punta Gorda recorded a statewide peak of of precipitation. The low moved northwestward and later curved northeastward, exiting into the Atlantic Ocean near Saint Augustine by early on July 2. Although it was initially disorganized as it moved offshore, the convection quickly developed in organization, and by 1800 UTC that day it had developed into Tropical Depression One about south of Charleston, South Carolina. reaching peak winds of . On its first advisory, a tropical storm watch was issued for from Baffin Bay, Texas, southward to Tampico, Tamaulipas. Nearing the coast of Mexico, the depression attained its peak intensity with winds of and a minimum pressure of . Failing to intensify further, Tropical Depression Two made landfall near La Pesca, Tamaulipas, on July 6. The National Hurricane Center issued the final advisory on July 7, although the circulation persisted until July 9 southwest of Texas. It produced an area of organized convection, and the depression intensified into Tropical Storm Bob roughly 18 hours after forming. and based on reports from the Hurricane Hunters, Bob attained hurricane status on August 17. After further intensification off the Carolinas, Bob reached peak winds of to the east of Virginia on August 19, making it a major hurricane. Significantly cooler sea surface temperatures resulted in weakening. After brushing Long Island, the center of Bob moved over Block Island, Rhode Island. About 40 minutes later it struck Newport, Rhode Island, with winds of , making it a Category 2 hurricane. It rapidly weakened to tropical storm intensity while moving through the remainder of New England, hitting Rockport, Maine, early on August 20. After crossing New Brunswick, Bob became extratropical in the Gulf of St. Lawrence and lasted another nine days before dissipating west of Portugal. One person each died in North and South Carolina, and about 10% of houses in the Outer Banks sustained minor roof damage. As the storm moved up the coast, heavy rain fell on the western side of the center. High winds left 300,000 people without power on Long Island. In neighboring Connecticut, strong winds downed trees across the region, with damage heaviest in the southeastern portion near the coast. Damage was heaviest as Bob made its final landfall, Monetary damage was greatest in Massachusetts, The heaviest rainfall from the hurricane fell at the Portland International Jetport in Maine, where fell during its passage. In Fredericton, New Brunswick, tropical storm-force winds downed trees and power lines.

Tropical Depression Four

One of the few vigorous tropical waves of the season emerged from the western coast of Africa with a large area of convection in late August. On August 24 it developed into a tropical depression near Cape Verde. Upon first forming, the depression had a circular area of convection near the center. It was initially well-organized, and on August 26 the depression dissipated to the west-southwest of the Cape Verde islands. Ultimately, the depression failed to organize significantly. By August 29, it had a broad and poorly organized circulation with only scattered convection. Due to cool water temperatures, the system was unable to maintain deep convection, and on August 31 the depression degenerated into a tropical wave about east of the Lesser Antilles.

Hurricane Claudette

The origins of Claudette were non-tropical, developing on September 4 about southeast of Bermuda from an upper-level disturbance. Following its formation, it developed slowly while moving southwestward, Conditions were favorable for development, with low wind shear and a large anticyclone providing outflow, or the outward wind flow from a storm. It underwent rapid intensification, and early on September 7 a reconnaissance flight reported that Claudette attained major hurricane status with winds of . Based on satellite estimates, Hurricane Claudette attained its peak intensity with winds of and a minimum pressure .

After peaking, Claudette began steady weakening. Around that time, a hurricane watch was issued for the island of Bermuda, which was later upgraded to a warning. The hurricane turned to the northwest, passing east of Bermuda as a Category 1 hurricane on September 8. Winds on the island peaked at , with gusts to , and waves reached up to in height. Upon developing, the depression had a broad circulation, located in an environment generally favorable for intensification. With a strong ridge to the north, the depression tracked steadily westward. The storm ultimately reached peak winds of , which it maintained for about 36 hours. On September 10 it attained its organizational maximum after developing a central dense overcast. Later that day, an upper-level low increased wind shear over the storm, As Danny approached the Lesser Antilles, it weakened to tropical depression status on September 11. Later that day, a Hurricane Hunters flight was unable to locate a closed circulation, which indicated that Danny degenerated into a tropical wave about east of the Lesser Antilles. The remnants tracked to the northwest and later to the north before being absorbed by a frontal system. Initially the center was difficult to locate on satellite imagery, but despite the proximity with Claudette, conditions were generally favorable for intensification. By late on September 9, the depression had become much better organized, and based on satellite estimates the NHC upgraded it to Tropical Storm Erika. It accelerated east-northeastward toward the Azores along the northern periphery of a ridge, briefly interacting with Claudette. Shortly thereafter it passed through the Azores, striking São Miguel Island. Nearby Santa Maria Island reported tropical storm force winds with gusts to , prompting the closure of the airfield for several hours. At 1300 UTC on October 15, a Hurricane Hunters flight observed sustained winds of to the southwest of the Isle of Youth. Based on the report, the NHC designated the system as Tropical Storm Fabian. although the NHC later assessed that the system developed as a tropical depression earlier that day. With a high pressure area to the north, there was already a large pressure gradient that had produced tropical storm force winds over the area. Initially the storm was disorganized, An eastward-moving upper-level trough imparted a northeast motion as well as unfavorable wind shear. The storm later moved through the Bahamas and became extratropical as it interacted with an approaching front. Before the storm hit the Cuban mainland, it produced wind gusts to in Cayo Largo del Sur. Its primary form of impact was from heavy rainfall in a 24‑hour period, peaking at in Caonao on the south coast of Cuba. In a six-hour period, Punta del Este recorded . As it passed east of the state, it dropped rainfall near the coast that peaked at in Conch Key. In the Florida Keys, the National Weather Service Office in Key West recorded sustained winds of with gusts to . Only isolated flooding happened from the precursor system to Fabian. Despite the presence of strong shear, the system was upgraded to a tropical depression at 2200 UTC on October 24 about east of the Lesser Antilles. By October 25, the circulation had become dissociated from the convection. The depression dissipated soon after without affecting land.

Hurricane Grace

On October 23 a mid-level low formed south of Bermuda. By two days later it had become a surface low, and on October 26 it developed into a subtropical storm. The system was labeled as such due to the initial lack of deep convection over the center, although following an increase in thunderstorms the NHC reclassified it as Tropical Storm Grace late on October 27. By that time, the storm had executed a path generally to the northwest. Grace continued to intensify and organize, and based on Hurricane Hunter reports the storm was upgraded to a hurricane early on October 28. Shortly thereafter, Grace turned sharply to the east due to the influence of a rapidly intensifying extratropical cyclone off the New England coast. An eye developed in the center of Grace, despite shallow convection.

As the hurricane accelerated eastward, it attained a peak intensity of on October 29. The rapid motion caused an asymmetry in the wind field, and the center passed approximately south of Bermuda without significantly affecting the island. contributing moisture to the developing extratropical storm that was eventually known as the Perfect Storm. but no damage was reported. The hurricane generated large swells along the East Coast of the United States,

Unnamed hurricane

The precursor of the season's final storm was a strong extratropical cyclone commonly known as the Perfect Storm. It evolved from an area of low pressure that developed off Atlantic Canada on October 28. The system moved southward and westward due to a ridge to its north, and reached its peak intensity. The storm lashed the East Coast of the United States with high waves and coastal flooding, before turning to the southwest and weakening. Moving over warmer waters, the system transitioned into a subtropical cyclone before becoming a tropical storm. It executed a loop off the Mid-Atlantic states and turned toward the northeast. On November 1 the system evolved into a full-fledged hurricane with peak winds of . The tropical system weakened, striking Nova Scotia as a tropical storm before dissipating.

Damage totaled over $200 million (1991 USD) and the death toll was thirteen. including the vacation home of George H. W. Bush, the president at the time. and along the coast high waves inundated roads and buildings. Off the coast of New York, a Coast Guard helicopter ran out of fuel and crashed, and although four members of its crew were rescued, one was killed. Two people died after their boat sank off Staten Island. High waves swept a person to their death in both Rhode Island and Puerto Rico, and another person was blown off a bridge in New York. This is the same list used for the 1985 season, with the exception of the names Erika and Grace, which replaced the names Elena and Gloria after that season. Both Erika and Grace were used for the first time in 1991.

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Ana
Bob
Claudette
Danny
Erika
Fabian
Grace

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Additionally, the October 1991 Perfect Storm later evolved into a hurricane; the National Hurricane Center left it unnamed due to the heavy damage and media interest in the predecessor extratropical storm.

Retirement

The World Meteorological Organization retired the name Bob from the Atlantic hurricane name lists following the 1991 season due to its high impact. The name was replaced with Bill for the 1997 season.

Season effects

This is a table of all of the storms that formed in the 1991 Atlantic hurricane season. It includes their name, duration, peak classification and intensities, areas affected, damage, and death totals. Deaths in parentheses are additional and indirect (an example of an indirect death would be a traffic accident), but were still related to that storm. Damage and deaths include totals while the storm was extratropical, a wave, or a low, and all of the damage figures are in 1991 USD.

Notes

References

External links

Monthly Weather Review
Detailed information on all storms from 1991
U.S. Rainfall information concerning 1991 tropical cyclones