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Allison never rose to hurricane status, but its impact went into the record books. The storm began as a tropical wave off Africa on May 21, Within five days, it had traveled west and over northern South America before continuing west across Central America and into the eastern Pacific on June 1. As the storm moved inland and quickly lost wind strength and tropical storm status, heavy rainfall records were set within the five days the storm lingered in Southeast Texas. The storm moved north across Houston on June 6, and the next day, Allison stalled near Lufkin as a depression.
It took a southwesterly turn on June 8 and by June 9, things began to get even more difficult. An analysis was later done on the path of Allison as it became a storm to remember.
It was the first tropical storm ever to have its name retired, alongside hurricanes like Katrina, Rita, Ike, and Harvey. The Tropical Prediction Center began to track the wave on May 21st after it moved off the west coast of Africa. Very little rainfall was associated with this system as it progressed westward and it eventually reached the Gulf of Tehuantepec off the western coast of Mexico on June 1st.
A disorganized area of thunderstorms then formed over the Gulf of Mexico as moisture associated with the remnants of the tropical wave interacted with an upper low located over South Texas on June 3rd and 4th. By the morning of Tuesday June 5th, Tropical Storm Allison formed about miles south of Galveston see figure below for a track of Allison.
The storm moved inland later that afternoon, quickly weakened, and became a tropical depression that evening as it drifted inland over Houston. Flooding would accompany Allison over the next four days as the remnants of the storm meandered north to Lufkin, southwest to between Huntsville and College Station, and then south to off the coast near Freeport. Why did Allison generate so much rainfall? The devastating flooding from Allison is a stark reminder that rainfall from tropical cyclones does not depend upon the strength of the system.
In other words, it does not matter if the tropical cyclone is a tropical depression with wind speeds up to 38 mph , a tropical storm winds of 39 to 73 mph , or a hurricane winds from 74 mph or greater. The Hydrometeorological Prediction Center has found six factors that impact the rainfall potential of landfalling tropical cyclones: the storm track or movement , time of day, storm size, topography, wind shear, and nearby weather features.
Allison was a small storm and the topography of Southeast Texas is rather flat; so, these two factors played a minor role. Between June 5th and the 9th, there was virtually no wind shear and no nearby weather features to affect the storm.
These were aided by an abundance of available Gulf moisture. On average, the steering currents over Southeast Texas during the tropical season are much weaker than for more northern latitudes.
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