A tropical wave moved off the west coast of Africa on May 21st. Tracking westward, it moved through the tropical Atlantic and Caribbean Sea…reaching the eastern Pacific Ocean on June 1st.A low level circulation formed on the 3rd south of Vera Cruz, and this system moved north into southeast Mexico steered by deep southwest flow. It emerged into the Bay of Campeche on the 4th as an area of thunderstorms, and guided north-northwest through the western Gulf of Mexico. The low became increasingly organized, and when reconnaisance aircraft investigated the system on the 5th, it had already become a tropical storm about 80 miles south of Galveston Texas. As it was steered by the subtropical ridge off the southeast, Allison moved north into Texas that evening,eventually tracking as far inland as Lufkin by the morning of the 7th. After already dropping ten or more inches of rain across portions of Texas and Louisiana, the cyclone began to move southward as a ridge over New Mexico strengthened just as the high off the southeast flattened and moved southeast. This set the stage for massive flooding in southeast Texas on on the 7th and 8th. The highest totals noted were 36.99 inches at the Port of Houston Texas, and 29.86 inches at Thibodaux Louisiana.Portions of Houston, Beaumont, Thibodaux, Lafayette, New Orleans, and Baton Rouge saw severe flooding from all this rain. Rains would continue into the 11th, as Allison moved back off the Texas coast, paralleling the coast of Louisiana before making a second landfall in the Teche region of the Bayou State.Reintensifying over land as it tracked through southeast Louisiana and southwest Mississippi,Allison formed an eye feature during the morning of the 11th, a rare accomplishment for a tropical cyclone over land. The system moved swiftly east-northeast crossing southern Mississippi and Alabama, central Georgia, and South Carolina, being steered by the subtropical jet stream to its north. Motion slowed as it approached a blocking ridge of high pressure off the coast of New England, which then allowed the cyclone to move northward along the coast of the Mid Atlantic and just offshore New England from the 16th through the 18th. Significant floods occurred in northeast North Carolina and southeast Pennsylvania during this time frame, with areas measuring 10 inches of rain within 6-12 hours. The last of the heavy rains with Allison escaped off the Eastern Seaboard during the early morning hours of the 18th.Damages as of this writing are estimated at $5 billion…with over $4 billion in the state of Texas.This makes Allison the most costly tropical cyclone in Texas history. Its track lies below. |
