Tropical Storm Allison was the first named storm of the 1989 Atlantic hurricane season. Allison formed off the middle Texas coast in late June, and, although weak, produced widespread flooding across portions of southeast Texas, western and west-central Louisiana, as high as 25 inches in some areas. Allison became one of Louisiana's wettest tropical cyclone's on record.
Allison caused $560,000,000 (1989 USD) in damage and killed 11 people, all directly.
|Formation||June 24, 1989|
|Dissipation||June 27, 1989|
|Highest winds||50 mph|
|Lowest pressure||999 mbar|
|Damages||$560,000,000 (1989 USD)|
|Areas affected||Texas, Louisiana|
|Part of the||1989 Atlantic hurricane season|
Allison developed from at least three distinct meteorological phenomena: the remnants of Eastern Pacific Hurricane Cosme, a westward-moving tropical wave, as well as a strong upper-level anticyclone draped across the Gulf of Mexico. The aforementioned factors, in combination with a ridge over the central plains were responsible for the environment in which Allison developed. A strong mid- to upper-level trough that had turned Cosme northward was replaced by a well-defined upper-level anticyclone that was centered across the entire Gulf of Mexico. During the period of June 22 through June 24, the aforementioned tropical wave entered the western Gulf of Mexico, causing an increase in deep convection over the area. At 1200 UTC June 23, Cosme's remnants were located just southwest of Brownsville, Texas. Over the following 24 hours, a new circulation center developed just off the upper Mexico coast. Based on surface observations along with data from offshore oil rigs, the system is estimated to have become Tropical Depression Two at 1800 UTC June 24. Over the following two days, the cyclone gradually organized, and the system became a tropical storm at 1200 UTC June 26 as per reconnaissance aircraft reports, although post-season analysis indicates that the cyclone had likely achieved tropical storm status prior to this point, at around 0000 UTC June 26. By 1200 UTC June 26, the ridge to the north of Allison began to erode as a frontal zone moved eastward across the western United States. Consequently, Allison began to move northward towards the middle Texas coast. By 1300 UTC June 26, Allison made landfall along the middle Texas coast near Matagorda Bay with a central pressure of 1002 mb. By 1200 UTC June 27, Allison was downgraded to a tropical depression, and by 0000 UTC June 28, Allison became extratropical.
On June 24, a Tropical Storm Watch was posted along the coast from Baffin Bay, Texas to Morgan City, Louisiana. On June 26, the watch was replaced by a Tropical Storm Warning. All watches and warnings were discontinued on June 27 as Allison moved inland and weakened.
Allison produced extreme and widespread flooding across portions of Texas and Louisiana, with upwards of over 25 inches in some locations. Allison produced a peak rainfall total of 25.67 inches at Winnfield, Louisiana.
Allison produced heavy rainfall in Arkansas, reaching 13.9 inches at one location. This is the highest rainfall total for a tropical cyclone in the state of Arkansas.
Heavy rainfall also spread across the Mid-Atlantic States, which produced some flooding. In Delaware, Allison's heavy rainfall led to record breaking discharge rates at three different gauge stations, while one third of the gauge stations reported significant discharges.
Allison killed a total of 11 people, all directly. Three deaths occurred in Texas, three in Louisiana, and five in Mississippi. Two teenage boys were killed when the raft they were aboard got sucked into a drainage pipe from the runoff in Beaumont, Texas. In Harris County, an 18 year old boy was killed via drowning. The deaths in Louisiana and Mississippi were also associated with drowning. Allison caused a total of $560,000,000 (1989 USD), primarily due to flooding.
Rainfall totals from Tropical Storm Allison.
Lack of Retirement
In spite of the damage, the name Allison was not retired by the World Meteorological Organization. It was, however, retired after its use during the 2001 season, being replaced with Andrea for the 2007 season.