Tropical Cyclone Report

Tropical Storm Bill

Bill made landfall on the Louisiana coast just west of Cocodrie as a 50-kt tropical storm.

a. Synoptic History

The interaction of a tropical wave with a mid- to upper-level low resulted in the formation of a surface low pressure area over the Yucatan Peninsula on 28 June. This system was accompanied by a large area of cloudiness and thunderstorms that extended eastward over the northwestern Caribbean Sea. Upper-level winds were marginally favorable for development but the interaction with land inhibited tropical cyclone formation. As soon as the low moved toward the north-northwest away from Yucatan, the convection became better organized. It is estimated that a tropical depression formed at 0600 UTC 29 June and reached tropical storm status by 1200 UTC on the same day.

Bill moved on a north-northwesterly to northerly track and, as the shear relaxed, the storm gradually intensified. It then turned to the north-northeast and reached its peak intensity of 50 knots, with a minimum pressure of 997 mb, at 1800 UTC 30 June when the cyclone's center was very near the coast. Initially, the convection and stronger winds were located to the northeast of the center due to wind shear from the southwest. Near landfall time, the wind field and convection became a little more symmetric as the shear relaxed. Bill made landfall near King Lake, about 20 miles west of Cocodrie on the south coast of Louisiana at its peak intensity around 1900 UTC 30 June. Thereafter, Bill weakened to a tropical depression as it moved toward the northeast over Central Mississippi and Alabama. It became an extratropical low near the border of Tennessee and Virginia by 1800 UTC 2 July and was absorbed by a frontal system by 0600 UTC 3 July.

The "best track" chart of the tropical cyclone's path is given in Figure 2, with the wind and pressure histories shown in Figure 3a and Figure 3b, respectively. The best track positions and intensities are listed in Table 1. To see radar and satellite loops at landfall click on Figure 1a and Figure 1b below:

Figure 1a: Radar loop for Tropical Storm Bill, 29 June - 2 July, 2003. (Note: large file 3.3MB)

Figure 1b: Satellite loop for Tropical Storm Bill, 29 June- 2 July, 2003. (Note: large file 3.1MB)

b. Meteorological Statistics

Observations in Tropical Storm Bill (Figure 3a and Figure 3b) include satellite-based Dvorak technique intensity estimates from the Tropical Analysis and Forecast Branch (TAFB), the Satellite Analysis Branch (SAB) and the U. S. Air Force Weather Agency (AFWA), as well as flight-level observations from flights of the 53^rd Weather Reconnaissance Squadron of the U.S. Air Force Reserve Command. Ship reports of winds of tropical storm force associated with Bill are given in Table 2, and selected surface observations from land stations and data buoys are given in Table 3.

Bill reached tropical storm status based on a report of 38 knots from the ship HG3Q located to the northeast of the developing center at 1200 UTC 29 June. Bill's peak intensity of 50 knots and minimum pressure of 997 mb were based on a report from a reconnaissance plane of 66 knots at 850 mb and a reliable minimum pressure of 997 mb surface observation from Lumcon Marine Center, near Cocodrie, respectively.

c. Casualty and Damage Statistics

There were four deaths associated with Bill. A 10-year old boy drowned in Holly Spring Creek in Raleigh, North Carolina, a man was killed by a falling tree in Atlanta, Georgia, and two swimmers drowned at Panama City Beach, Florida in rip currents produced by Bill. The wind damage was confined to downed branches and trees across the eastern portion of southeast Louisiana and coastal Mississippi where there were power outages. The most significant storm surge flooding was noted in coastal sections of southeast Louisiana primarily in southern Terrebone Parish where the local levee was breached and overtopped in the Montegut area. This resulted in some homes being flooded. An F1 (Fujita Scale) tornado touched down in Reserve, Louisiana around 1710 UTC 30 June, hitting a private school and causing significant damage to several buildings. It then hit a mobile home park damaging at least 20 homes. The Property Claim Services Division of the Insurance Service Office reports that insured losses due to Bill totaled 22 million dollars in Louisiana. Total losses for Louisiana and Mississippi are estimated at $50 million.

d. Forecast and Warning Critique

Advisories on the tropical cyclone were initiated when early morning visible images confirmed the presence of a well-defined center of circulation. Concurrently, a report from a ship indicated that the winds had reached tropical storm strength-hence there were no tropical depression advisories. This transition can occur when a strong pressure gradient prevails before a system in formative stage develops a closed circulation. However, a post-analysis suggests that a tropical depression may have formed six hours earlier, as indicated in the best track.

Bill was a short-lived tropical cyclone and the number of forecasts is quite small. The average official track errors were 54, 96,146 and 189 n mi for the 12, 24, 36, 48 h forecasts, respectively¹. These errors are greater than the average official track errors for the 10-yr period 1993-2002 of 45, 81, 116, 150 n mi, respectively, Table 4 includes a summary of all track guidance during Bill. Average official intensity errors were 4, 6, 3 and 1 kt for the 12, 24, 36, 48 h forecasts, respectively. For comparison, the average official intensity errors over the 10-yr period 1993-2002 are 6, 10, 13, and 15 kt, respectively.

Table 5 lists the watches and warnings associated with Tropical Storm Bill.

The weather activity that became Tropical Storm Bill was first described in the Tropical Weather Outlook issued at 1130 am EDT June 24, more than 6 days prior to landfall. After genesis, the potential for intensification was stated in all the public and forecast advisories. The tropical storm warning was issued 22 hours prior to landfall. Although Bill made landfall within the area of warning, it is always difficult to precisely forecast the point of landfall. Figure 4 shows the track guidance available at 0600 UTC 30 June. Note that none of the models captured the north-northeastward turn of Bill prior to landfall.

¹All forecast verifications in this report include the depression stage of the cyclone. National Hurricane Center verifications presented in these reports prior to 2003 did not include the depression stage.

Figure 2: Best track positions for Tropical Storm Bill, 29 June- 2 July, 2003. Track after landfall is based on analyses from the NOAA Hydrometeorological Prediction Center.

Figure 3a: Selected wind observations and best track maximum sustained surface wind speed curve for Tropical Storm Bill, 29 June-2 July, 2003. Aircraft observations have been adjusted for elevation using 90%, 80%, and 80% reduction factors for observations from 700 mb, 850 mb, and 1500 ft, respectively. Estimates after landfall are based on analyses from the NOAA Hydrometeorological Prediction Center.

Figure 3b: Selected pressure observations and best track minimum central pressure curve for Tropical Storm Bill, 29 June-2 July, 2003. Estimates after landfall are based on analyses from the NOAA Hydrometeorological Prediction Center.

Figure 4: Available track guidance for Bill at 0600 UTC 30 June. The best track is given by the easternmost gray line with positions given at 6 h intervals. Note that 12 hour prior to landfall, none of the models indicated the north-northeastward turn of Bill.