Tropical Storm Allison - June 4-18, 2001
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

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.


Below is a map showing storm total rainfall amounts deposited by Allison in southeast Texas.,  Note the variability
of the rainfall pattern at this small of a scale.  Data from the National Climatic Data Center, Harris Country of Emergency
Managment rainfall mesonet, and the Texas Draining District 6 rainfall mesonet for Jefferson County was used in the
construction of this map.  The legend for the rainfall amounts is seen on the maps below.

Southeast Texas Rainfall from Allison (2001) Allison (2001) Filled Contour Rainfall Graphic
White background, filled color contour of rainfall from Allison in Southeast Texas

Below is the storm total rainfall map for Allison for the Gulf coast.  Note the maxima in the proximity of
the two points of landfall in southeast Texas and southeast Louisiana.  It should be noted that much of
the rainfall in southeast Louisiana occurred days before the center passed directly over the site.

Gulf coast rainfall from Allison (2001) Allison (2001) Southeast Rainfall Filled Contour Graphic
Filled contour rainfall on white background for Allison (2001)

 Below is the overall storm total map for the United States showing Allison's swath of rainfall.

Tropical Storm Allison (2001) Rainfall Allison (2001) Filled Contour Rainfall Graphic for the United States
Color filled rainfall for Allison (2001) on a white background

 Below is the calendar for Daily Precipitation Maps.  Note that the 24-hour periods end
at 12z that morning.

Sun Mon Tue Wed Thu Fri Sat

5 6 7 8 9
10 11 12 13 14 15 16
17 18