Tropical Storm Allison was the first named storm of the 2001 Atlantic hurricane season. Allison developed in the Gulf of Mexico south of Galveston on June 4. It strengthened into a tropical storm before striking near Houston, Texas late on June 5. After landfall, Allison stalled over central Texas, producing widespread flash flooding over cental and southeastern Texas. It caused Houston's worst natural disaster in history when it flooded the city. Allison re-emerged into the Gulf of Mexico early on June 10, and strengthened into a subtropical storm after it made landfall in central Louisiana. Allison then moved east-northeast across the Southeastern United States and Eastern United States, then emerged into the Atlantic Ocean near New Jersey, strengthened into a subtropical storm again, then weakened as it moved northeast and out to sea. Allison was the first tropical storm to strike the upper Texas coastline since Tropical Storm Frances in 1998.

Allison killed 55 people, 41 direct, 14 indirect. It caused $5.5 billion (2001 USD) in damage, nearly all in Houston; damage from Tropical Storm Allison may have gotten close to $13 billion in actual cost.

Tropical Storm Allison on June 5
Formation June 4, 2001
Dissipation June 18, 2001
Highest winds 60 mph
Lowest pressure 1000 mbar
Deaths 40 direct, 14 indirect
Damages $5.5 billion (2001 USD)
Areas affected Texas, Louisiana, Southeastern United States, Eastern United States

Meteorological History

On May 21, a tropical wave moved off the coast of Africa. The wave moved westward across the unfavorable Atlantic Ocean, maintaing little convection as it did so. After it moved across South America and the southwestern Carribean Sea, the wave entered the eastern North Pacific Ocean on June 1. On June 2, a low-level circulation center developed within the wave while it was located about 230 miles south-southeast of Salina Cruz, Mexico. Southerly flow forced the wave northward, and it moved inland on June 3. Overland, the low-level circulation dissipated, but the mid-level circulation center persisted. On June 4, the wave entered the Gulf of Mexico, where deep convection developed on its eastern side. On June 5, the wave managed to bring its mid-level circulation down to the surface, and it is estimated that Tropical Storm Allison formed from this wave on June 5, while located only 140 miles south of Galveston, Texas. After forming, Allison had subtropical characteristics, as it interacted with an upper-level low to the southwest. Despite this, Allison rapidly strengthened to reach peak winds of 60 mph on June 5. At this time, tropical storm-force winds extended 230 miles east of the center. While nearing the Texas coastline, Allison weakened to a 50 mph tropical storm. It struck near Freeport, Texas late on June 5 as a 50 mph tropical storm. After landfall, Allison quickly weakened, and the National Hurricane Center ceased writing advisories for the system early on June 6. The depression moved very slowly northward until reaching Lufkin Texas, where it stalled due to a ridge of high pressure to the north. On June 8, the depression moved south, then southwest. Early on June 10, Allison re-emerged into the Gulf of Mexico, just 22 miles west of its original landfall location. brody was here

Due to dry air and moderately strong vertical wind shear, Allison transitioned into a subtropical depression. As Allison moved eastward, and new circulation center developed on its east side. On June 11, Allison made landfall near Morgan City, Louisiana. Deep convection re-developed over Allison's circulation center while it was over southeastern Louisiana, and it strengthened into a subtropical storm because of this. Allison reached 45 mph winds as a subtropical storm, and an eye feature briefly existed in the storm.


Allison over Mississippi with an eye-like feature.

The feature was temporary, however, and Allison quickly weakened back to a tropical depression. The depression tracked to the east-northeast through Mississippi, Alabama, Georgia, and South Carolina before becoming nearly stationary near Wilmington, North Carolina. Allison drifted through North Carolina, and accelerated to the northeast in response to an approaching cold front. On June 17, Allison entered the Atlantic Ocean near New Jersey, and briefly re-strengthened to a subtropical storm again due to baroclinic processes. Allison became extratropical south of Long Island on June 18, and then became absorbed by the cold front on June 19.


Allison over South Carolina.


Shortly after forming, officials in Galveston County, Texas issued a voluntary evacuation for the western end of Galveston Island. This evacuation order was issued for fear of coastal flooding, since the Galveston Seawall did not protect that area. Also, the ferry from Galveston Island to the Bonivar Peninsula was closed, and voluntary evacuations were issued for the city of Surfside in Brazoria County. Also, voluntary evacuations were put into effect near Sabine Pass in Jefferson County, although few people actually evacuated. When the National Hurricane Center issued the first advisory on Allison, Tropical Storm Warnings were issued from Sargent, Texas to Morgan City, Louisiana, just 3 hours before Allison brought tropical storm-force winds.

After Allison made landfall, Flash Flood Watches and Flash Flood Warnings were issued for numerous areas of eastern Texas. In addition, travel was discouraged because of the threat of flash flooding from Allison. During the flood event, the National Weather Service in Houston issued 99 flash flood warnings with an average lead time of 40 minutes. In addition, there were only nine warnings that were false alarms. With an average lead time of 24 minutes, the National Weather Service in Lake Charles, Louisiana issued 47 flash flood warnings, of which eleven were false alarms. Also, one flash flood occured outside of the warned area. With an average lead time of 39 minutes, the National Weather Service in New Orleans/Baton Rouge issued 87 flash flood warnings, of which 30 were not followed by a flash flood. In addition, there were five flash floods not covered in the warning area.

Finally, in Tallahassee, Florida, one shelter was opened up a day prior to Allison's moving through the area, with seven staff members housing 12 people. Two other shelters were put on standby. Also, teams informed citizens in the Florida Panhandle of the threat of flooding from Allison.


Throughout its entire life from Texas to the Mid-Atlantic region of the United States, Allison produced significant flash flooding. The worst of the flooding occured in Houston, Texas, where 35 over 35 inches of rain fell. In addition, Allison killed 54 people; 41 direct, 14 indirect. 27 of the 41 drowned from flooding. Finally, Allison caused over $5,000,000,000 (2001 USD) in damage, making it the costilest and deadliest tropical storm on record in the United States.


Allison made landfall with a storm surge of two to three feet. Combined with waves on top, areas of Galveston Island experienced a wall of water 8 feet (2.5 m) in height, creating overwash along the coastline. The storm caused winds of up to 43 mph (69 km/h) at the Galveston Pier. While Allison was stalling over Texas, it dropped heavy rainfall across the state, including 9.77 inches (248 mm) in Galveston, 12.13 inches (308 mm) in Jamaica Beach, Texas, and other similar totals along the coast. Minimal beach erosion was reported. Impact was minimal near the coast.

While moving northward through Texas as a minimal tropical depression, Allison produced minor wind gusts. Shortly after making landfall, the storm spawned a tornado in Manvel of Brazoria County, causing damage to one home. Within hours of making landfall, rainfall totals of 8 to 12 inches (200 to 300 mm) were common in Galveston and Harris County. Flash flooding continued for days,[12] with rainfall amounts across the state peaking at just over 40 inches (1033 mm) in northwestern Jefferson County. In the Port of Houston, a total of 36.99 inches (940 mm) was reported.

The Southwest Freeway, near Downtown Houston, lies under water due to flooding from Tropical Storm Allison. Houston experienced torrential rainfall in a short amount of time. 6.3 inches (160 mm) fell in just one hour, while 28.5 inches (724 mm) fell in only 12 hours. The six-day rainfall in Houston amounted to 38.6 inches (980 mm). Two-thirds of the bayous and creeks in Harris County experienced 500-year flood events. Houston, which typically receives 46.07 inches (1170 mm) of rain in a year, experienced 35.7% of its expected total in the first nine days of June.

The deluge of rainfall flooded 95,000 automobiles and 73,000 houses throughout Harris County. Tropical Storm Allison destroyed 2,744 homes, leaving 30,000 homeless with residential damages totaling to $1.76 billion (2001 USD, $1.94 billion 2006 USD). Residential neighborhoods inside and to the north of Interstate 610 were hardest hit.

Several hospitals in the Texas Medical Center, the largest medical complex in the world, experienced severe damage from the storm, which hit quickly and with unexpected fury on a Friday evening. Hospital personnel were forced to evacuate thousands of patients in a major effort that included Coast Guard and Army helicopters. Many of the hospitals had lost all power, including back-up generators, meaning that patients had to be carried down dark stairwells by the staff in temperatures over 100 degrees. Patients who could not breathe on their own had to be continuously hand-pumped during the evacuation, which lasted hours. Most hospitals lost power and backup power when basements, the area where power and research data were kept, flooded. The Baylor College of Medicine experienced major damage, totaling $495 million (2001 USD, $547 million 2006 USD). The medical school lost 90,000 research animals, 60,000 tumor samples, and 25 years of research data. The University of Texas Health Science Center at Houston, across the street, lost thousands of laboratory animals, including expensive genetic-specific mice. Decades of research was lost, including, for many scientists, their life's work. The UT-Houston gross anatomy lab, cyclotron, and other important facilities were completely destroyed. Throughout the Medical Center, damage totaled to over $2 billion (2001 USD, $2.2 billion 2006 USD). Most were reopened after a month, though it took much longer to become fully operational.

The underground tunnel system, which connects most large office buildings in downtown Houston, was submerged, as were many streets and parking garages adjacent to Buffalo Bayou. At the Theatre District, also in downtown, the Houston Symphony, Houston Grand Opera, and Alley Theater lost millions of dollars of costumes, musical instruments, sheet music, archives and other artifacts. Local television stations ran all-night coverage of the deluge from June 8 through the next day, including KHOU-TV 11, which was forced to transmit its broadcast to a satellite truck when floodwaters entered its near-downtown production studio. By midnight June 9 nearly every freeway and major road in the city was under several feet of water, forcing hundreds of motorists to abandon their vehicles for higher ground. Eighteen-wheeled trucks were filmed floating down major freeways and highways, swept along by floodwaters.

Despite massive flooding damage to entire neighborhoods there were no drowning deaths in flooded homes. In the area, there were 12 deaths from driving, 6 from walking, 3 from electrocution, and 1 in an elevator. Elsewhere in Texas, a man drowned when swimming in a ditch in Mauriceville. Damage totaled to $5.2 billion (2001 USD, $5.7 billion 2006 USD) throughout Texas.

Though Allison's flooding was extreme, it was not unprecedented. Tropical Storm Amelia in 1978 dropped over 46 inches (1170 mm) of rainfall in Bluff, Texas, which remains the record highest rainfall for a single storm in the state of Texas. In addition, Tropical Storm Claudette in 1979 and a hurricane in 1921 produced rainfall totals of over 40 inches (1015 mm).

The Southwest Freeway near downtown Houston underwater.


While making its first landfall, Allison's large circulation dropped severe rains on southwest Louisiana. Days later, Allison hit the state as a subtropical storm, dropping more heavy rains to the area. Rainfall totals peaked at 29.86 inches (758 mm) in Thibodaux, the highest rainfall total in Louisiana from a tropical cyclone since a previous Tropical Storm Allison in 1989. Most of the southeastern portion of the state experienced over 10 inches of rain (255 mm). Winds were generally light, peaking at 38 mph (61 km/h) sustained in Lakefront with gusts to 53 mph (85 km/h) in Bay Gardene. The storm produced a storm surge of 2.5 feet (0.75 m) in Cameron as it was making landfall in Texas. While moving northward through Texas, the outer bands of the storm produced an F1 tornado near Zachary, damaging several trees and a power line. A man was killed when a damaged power line hit his truck.

When Allison first made landfall, heavy rainfall flooded numerous houses and businesses. Minor wind gusts caused minor roof damage to 10 houses in Cameron Parish, while its storm surge flooded portions of Louisiana Highway 82. When the system returned, more rainfall occurred, flooding over 1,000 houses in St. Tammany Parish, 80 houses in Saint Bernard Parish, and hundreds of houses elsewhere in the state. The flooding also forced 1,800 residents from their homes in East Baton Rouge Parish. The deluge left numerous roads impassable, while runoff resulted in severe river flooding. The Bogue Falaya River in Covington crested past its peak twice to near record levels. The Amite and Comite Rivers reached their highest levels since 1983. In addition, the levee along the Bayou Manchac broke, flooding roadways and more houses. Damage in Louisiana totaled to $65 million (2001 USD, $72 million 2006 USD).


Flooding in Chackbay.

South - Eastern United States

In Mississippi, Allison produced heavy rainfall of over 10 inches (255 mm) in one night, while some areas in the southwestern portion of the state received over 15 inches (380 mm). The flooding damaged numerous houses and flooded many roadways. Thunderstorms from the storm produced four tornadoes, including one in Gulfport, Mississippi that damaged 10 houses. Severe thunderstorms in George County damaged 15 houses, destroyed 10, and injured five people. Damage in Mississippi totaled to over $1 million (2001 USD, $1.1 million 2006 USD). Rainfall in Alabama was moderate, with areas near Mobile experiencing more than 10 inches (255 mm). Heavy rainfall closed several roads in Crenshaw County. The storm, combined with a high pressure, produced coastal flooding in southern Alabama. Allison produced an F0 tornado in southwest Mobile County that caused minor roof damage and another F0 tornado in Covington County that caused minor damage to six homes and a church.

The storm, combined with a high pressure system, produced a strong pressure gradient, resulting in strong rip currents off the coast of Florida. The currents prompted sirens, which are normally used for storm warnings, to be activated in Pensacola Beach. The rip currents killed 5 off the coast of Florida. Outer rain bands from the storm dropped heavy rainfall across the Florida Panhandle of over 11 inches (280 mm) in one day. The Tallahassee Regional Airport recorded 10.13 inches (257 mm) in 24 hours, breaking the old 24 hour record set in 1969. Throughout the state, Allison destroyed 10 homes and damaged 599, 196 severely, primarily in Leon County. Including the deaths from rip currents, Allison killed eight people in Florida and caused $20 million (2001 USD, $22 million 2006 USD) in damage.

Over Georgia, the storm dropped heavy rainfall of 10 inches (255 mm) in 24 hours in locations. The deluge caused rivers to crest past their banks, including the Oconee River at Milledgeville which peaked at 33.7 feet (10.3 m). The rainfall, which was heaviest across the southwestern portion of the state, washed out several bridges and roads, and flooded many other roads. Georgia governor Roy Barnes declared a state of emergency for seven counties in the state. The storm also spawned two tornadoes. In South Carolina, Allison's outer bands produced 10 tornadoes and several funnel clouds, though most only caused minor damage limited to a damaged courthouse, snapped trees and downed power lines. Allison produced from 12 to 16 inches (305 to 406 mm) of rainfall in North Carolina, closing nearly all roads in Martin County and damaging 25 homes. The severe flooding washed out a bridge in eastern Halifax County and flooded numerous cars. Wet roads caused nine traffic accidents throughout the state.

Mid-Atlantic States and North - Eastern United States

In Virginia, Allison produced light rainfall, with the southeastern and south-central portions of the state experiencing over 3 inches (76 mm). A tree in a saturated ground fell over and killed one person. Allison also produced one tornado in the state. Washington, D.C. experienced moderate rainfall from the storm, totaling to 2.59 inches (66 mm) in Georgetown. In Maryland, rainfall from Tropical Depression Allison totaled to 7.5 inches (190 mm) in Denton, closing eleven roads and causing washouts on 41 others. The Maryland Eastern Shore experienced only minor rainfall from one to two inches (25 to 50 mm). Damage was light, and no deaths were reported. In Delaware, the storm produced moderate rainfall, peaking at 4.2 inches (106 mm) in Greenwood. No damage was reported.

Allison, in combination with an approaching frontal boundary, dropped heavy rainfall across southeastern Pennsylvania, peaking at 10.17 inches (258 mm) in Chalfont in Bucks County and over 3 inches (76 mm) in portions of Philadelphia. The rainfall caused rivers to rise, with the Neshaminy Creek in Langhorne peaking at 16.87 feet (5 m). Several other rivers and creeks in southeastern Pennsylvania crested at over 10 feet (3 m). The rainfall downed numerous weak trees and power lines, leaving 70,000 without power during the storm. The flooding washed out several roads and bridges, including a few SEPTA rail lines. In addition, the rainfall destroyed 241 homes and damaged 1,386 others. Flooding at a Dodge dealership totaled 150 vehicles. Hundreds of people were forced to be rescued from damaged buildings from flood waters. The flooding dislodged a clothes dryer in the basement of the "A" building of the Village Green Apartment Complex in Upper Moreland Township, breaking a natural gas line. The gas leak resulted in an explosion and an ensuing fire that killed six people. Firefighters were unable to render assistance as the building was completely surrounded by floodwaters. Additionally, one man drowned in his vehicle in a river. Damage in Pennsylvania totaled to $215 million (2001 USD, $237 million 2006 USD).

In New Jersey, the storm produced heavy rainfall, peaking at 8.1 inches (205 mm) in Tuckerton. The rains also caused river flooding, including the north branch of the Metedeconk River in Lakewood which crested at 8 feet (2.5 m). The flooding, severe at places, closed several roads, including numerous state highways. Gusty winds of up to 44 mph (71 km/h) in Atlantic City downed weak trees and power lines, leaving over 13,000 without power. Several people had to be rescued from high waters, though no fatalities occurred in the state. Overall damage was minimal.

Tropical Storm Allison caused flash flooding in New York, dropping up to 3 inches (75 mm) of rain in one hour in several locations and peaking at 5.73 inches (146 mm) in Granite Springs. The rains also caused river flooding, including the Mahwah River which crested at 3.79 feet (1 m). Allison's rainfall damaged 24 houses and several stores, while the flooding closed several major highways in the New York City area. Overall damage was light, and no fatalities occurred in New York due to Allison. Similarly, rainfall in Connecticut peaked at 7.2 inches (183 mm) in Pomfret, closing several roads and causing minor damage to numerous houses. The Yantic River at Yantic crested at 11.1 feet (3.4 m), while a state road was closed when a private dam in Hampton failed from the rainfall. In Rhode Island, Allison produced up to 7.1 inches (180 mm) of rainfall in North Smithfield, washing out several roads and houses, and destroying a log house in Foster.

An isolated severe thunderstorm in the outer bands of Allison produced an F1 tornado in Worcester and Middlesex Counties in Massachusetts, impacting over 100 trees and damaging one house and one small camper. A microburst in Leominster and another in Shirley damaged several trees. Lightning from the storm hit two houses, causing significant damage there but little elsewhere. Allison also produced moderate rainfall in the state, mainly ranging from 3 to 5 inches (75 to 125 mm). The rainfall caused drainage and traffic problems. Damage in Massachusetts totaled to $400,000 (2001 USD, $440,000 2006 USD).

Flood damage in Pennsylvania.


Because the damage was extensive and widespread, the World Meteorological Organization retired the name Allison in the Spring of 2002. It was replaced with Andrea for the 2007 Atlantic hurricane season. Allison can never be used again for an Atlantic or Gulf hurricane or tropical storm. This was the 2nd hit on Texas Allison performed, the first twelve years before during 1989.

See Also

2001 Atlantic hurricane season


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