Crawfish Tales
A Quarterly Publication of the National Weather Service Lower Mississippi River Forecast Center
Slidell, Louisiana


David Reed, Hydrologist In Charge Vol. 6 No. 2, Winter 2003 Ethan A. Jolly, Editor


Features Tropical Overview: Tropical Storm Isidore and Hurricane Lili Know Your River Systems: Central Tennessee

From the HIC

Wow! What a busy Hurricane Season! The LMRFC area was affected by tropical systems Bertha, Faye, Hanna, Isidore, and Lili during the 2002 Hurricane Season. As you will see in this newsletter, significant flooding resulted from the last two. The LMRFC was up to the challenge and the staff provided outstanding support to our WFOs and other partners and users. Congratulations to the staff at the LMRFC for a job well done!

We do not expect the forecast challenges to ease up any time soon. Since Hurricane Lili, much of the the LMRFC areas had unusually heavy rainfall for the Fall season with significant flooding occurring over much of Louisiana and Mississippi. When coupling this with predictions of above normal rainfall for the next three months because of El Nino conditions, we are expecting an active and long flood season for 2003.

I would be remiss in not “bragging” about the LMRFC. In October, the LMRFC received the Department of Commerce Bronze Medal for providing critical forecasts and services to our customers and partners during Tropical Storm Allison in June, 2001. Congratulations to the LMRFC staff for an award well deserved!

As you can see, we are expecting an active flood season for 2003. However, we always enjoy hearing from our cooperators and partners. Please let us know if there are additional things we can do to provide you service.

- Dave Reed


Tropical Overview: Tropical Storm Isidore and Hurricane Lili

Conditions had been relatively dry across much of the LMRFC area during the summer. However, the last week of September and first week of October brought two tropical systems to the area. Tropical Storm Isidore and Hurricane Lili produced copious amounts of rainfall and caused mainly minor to moderate flooding across numerous river basins in southeast Louisiana, much of Mississippi and western Tennessee.

Tropical Storm Isidore
Isidore began as a tropical depression in the Windward Islands in mid September. By the time Isidore moved into the Gulf of Mexico, it was a category three hurricane. On September 22nd, Isidore moved inland over the Yucatan Peninsula and weakened. Over the next few days Isidore moved northward over the Gulf of Mexico and made landfall early on the 26th just west of Grand Isle, Louisiana, as a 70 mph tropical storm. As Isidore moved inland, heavy rainfall occurred mainly over Louisiana, Mississippi, and Tennessee. Rainfall averaged 6 to 10 inches over almost the entire state of Mississippi, southeast Louisiana, and parts of western Tennessee. Some areas in central Mississippi received up to 15 inches of rain, with parts of the New Orleans metro area reporting more than 15 inches of rain. Rainfall associated with Tropical Storm Isidore is shown in Figure 1. Isidore caused

Figure 1: Stage III Precipitation Estimates from 09-24-2002 through 09-27-2002
Stage III Precipitation Estimates from 09-24-2002 through 09-27-2002
Click for larger image

major flooding along the Tchefuncta River in southeast Louisiana. Otherwise, mainly minor to moderate flooding occurred across parts of southeast Louisiana, much of Mississippi and parts of west Tennessee. Minor tidal induced (storm surge) flooding also occurred in southeast Louisiana along the lower Amite River. Figure 2 shows the extent and category of flooding by basin caused by Isidore.

Figure 2 : Flood Crests due to Tropical Storm Isidore
Flood Crests due to Tropical Storm Isidore
Click for larger image

Hurricane Lili
Hurricane Lili began as a tropical depression in the Atlantic Ocean on September 21st. As Lili moved across the Gulf of Mexico it reached category four status with sustained winds up to 145 mph. In the early morning of October 3rd, Lili began weakening as it approached the Louisiana coast. Lili moved inland over Vermilion Bay on the central Louisiana coast around 8:00am on the 3rd as a category two storm. Heavy rains associated with Lili were mainly confined to the area near the center of the storm as it moved northward through central Louisiana, and then turned to the northeast toward northern Mississippi. 5 to 7 inches of rain fell over the Vermilion River and parts of the lower Ouachita River as the center of the storm passed over these areas. Additional heavy rain occurred in some of the outer bands as they moved through southeast Louisiana and southern Mississippi, with the lower Pearl River and the drainages on the Northshore of Lake Pontchartrain receiving 4 to 7 inches of rain. Much of this area had moderate to heavy rains the week before with Isidore. Rainfall associated with Hurricane Lili is shown in Figure 3.

Figure 3 : Stage III Precipitation Estimates from 10-02-2002 through 10-05-2002
Stage III Precipitation Estimates from 10-02-2002 through 10-05-2002
Click for larger image

Flooding from Lili generally occurred across the same areas affected by Isidore but was less widespread. Some additional minor flooding occurred across parts of southwest Louisiana. There was also some moderate tidal (storm surge) induced flooding across the lower Atchafalaya and Vermillion Rivers in south-central Louisiana and the Jordon River in coastal Mississippi. Figure 4 shows the extent and category of flooding by basin caused by Lili.

Figure 4 : Flood Crests due to Hurricane Lili
Flood Crests due to Hurricane Lili
Click for larger image

- Carolyn Levert and Angelo Dalessandro

Know Your River Systems: Central Tennessee

The rivers across Middle Tennessee and Northern Alabama stretch from parts of the Cumberland Plateau in the east to rolling hills of the Lower Tennessee Valley in the west. All of the rivers in this area flow into the Tennessee River which is regulated with numerous locks and dams owned and operated by the Tennessee River Authority(TVA).

Figure 1 shows the major rivers, streams, and topography in the region. TVA operates Tims Ford Reservoir to regulate the Elk River. This reservoir also acts as flood control for the largest city on the Elk River, Fayetteville TN. In

Figure 1: Central Tennessee and Northern Alabama
Central Tennessee and Northern Alabama
Click for larger image

addition to flood control, Tims Ford Reservoir is used for recreation and power generation with two generators capable of producing a total of 40 mega-watts of power. TVA regulates the Duck River with Normandy Reservoir. This reservoir provides flood control for cities downstream along with recreation. Major cites that are situated on the Duck River are Shelbyville, Columbia and Centerville. Some of the smaller tributaries in Middle Tennessee are the Buffalo, Shoal Creek, Paint Rock, and Flint River, which flows just east of Huntsville AL.

Hydro-Climotology of the Area
Precipitation is uniform throughout the year with an average of between 55 and 60 inches of rain annually. The rivers in this area usually crest in about 12 hours for the headwaters to 2 days at the more downstream locations.

History of the Area
Table 1 shows each of the rivers and LMRFC forecast points with flood stage, record flood, and most recent flood information given. Major flooding occurred on the Elk River at Fayetteville in December 1990. Over 10 inches of rain in ths area over a 3 day period contributed to this flood. Fayetteville also experienced major flooding in March 1973 as 6.62 inches of rainfall fell in a 24 hour period. Over 10 inches of rainfall in a 2 day period contributed to the major flooding along the Buffalo River in May 1991. Recently, major flooding occurred in January 2002 along the Duck River where between 5 and 8 inches of rainfall fell over a 2 day period.

Table 1: Record and Recent Flooding
River Location Flood Stage (ft) Record Recent Flood (stage/date)
Elk Fayetteville 17.5 29.5 ft 12/1990 19.4 ft 3/2002
  Prospect 26 40.9 ft 3/1902 30.8 ft 1/2002
Shoal Creek Iron City 14 28.1 ft 3/1902 14.5 ft 3/2002
Duck Shelbyville 25 42.1 ft 3/1926 26.1 ft 3/2002
  Columbia 32 51.8 ft 2/1948 37.8 ft 3/2002
  Hurrican Mills 24 30.7 ft 2/1948 24.0 ft 1/2002
Buffalo Lobelville 10 25.3 ft 5/1991 10.7 ft 5/2002
Paint Rock Woodville 16 24.4 ft 3/1973 17.2 ft 5/2002
Flint Chase 16 29.5 ft 3/1973 16.4 ft 3/1994

- Eric Jones
 

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