ASSESSMENT OF THE IMPACTS OF TWO TROPICAL CYCLONES ON THE NORTHERN GULF OF MEXICO COAST: SEPTEMBER-OCTOBER, 2002

In 2002 for the first time in recorded history, coastal Louisiana was struck by two tropical cyclones only seven days apart. Tropical Storm Isidore made landfall along the Caminada Moreau Headland on September 26 and Hurricane Lili came ashore near Marsh Island on October 3, 2002. Both storms were unique in many ways; Isidore although loosely organized, developed sea state that affected beaches all along the northern Gulf of Mexico. The strength of Lili on the other hand, generated waves in excess of 12 m (>40 ft.) when she was a Category 4 storm in the central GOM. The storms' trajectory brought both close to several ocean observing stations (WAVCIS) that subsequently provided comprehensive and unique data sets; one station (CSI 3) was located in the eye wall of Lili.

Respective wave fields established by both systems demonstrate the characteristics of the storms. For example, the spectral evolution shows distinctly longer duration of storm waves due to Isidore (5 days) when compared to Lili (2 days). Assuming an arbitrary but realistic cut off frequency of 0.2 Hz for differentiating sea from swell in the Gulf of Mexico, two distinct peaks in wave energy occur about 0.08 Hz at CSI 05 separated by 3 days. The first occurred when Isidore was a strong hurricane traversing the Yucatan whereas the second is attributed to the system moving landward towards Louisiana. Rapid evolution of the wave field due to Lili began approximately 6 days later although having considerably less duration than Isidore because of the fast forward speed of the system. TS Isidore's general south-north path generally paralleled 5 observation stations from the central GOM (42001) north to Terrebonne Bay, a distance of approximately 400 km. A detailed time series of significant wave height attributable to Isidore is presented along with several important findings indicating the significant control exercised by local geology on wave and surge hydrodynamics.