In August 2005, the eye of Hurricane Katrina passed 90 km to the west of a 3-m discus buoy deployed in the Mississippi Sound and operated by the Central Gulf of Mexico Ocean Observing System (CenGOOS). The buoy motions were measured with a strapped-down, 6 degrees of freedom accelerometer, a three-axis magnetometer, and from the displacement of a GPS antenna measured by postprocessed-kinematic GPS.Recognizing that an accelerometer experiences a large offset due to gravity, the authors investigated four different means of computing wave heights. In the most widely used method for a buoy with a strapped-down, 1D accelerometer, wave heights are overestimated by 26% on average and up to 56% during the peak of the hurricane. In the second method, the component of gravity is removed from the deck relative z-axis accelerations, requiring pitch and roll information. This is most similar to the motion of the GPS antenna and reduces the overestimation to only 5% on average. In the third method, the orientation data are used to obtain a very accurate estimate of the vertical acceleration, reducing the overestimation of wave heights to 1%. The fourth method computes an estimate of the true earth-referenced vertical accelerations using the accelerations from all three axes but not the pitch and roll information. It underestimates the wave heights by 2.5%. The fifth method uses the acceleration from all three axes and the pitch and roll information to obtain the earth-referenced vertical acceleration of the buoy, the most accurate measure of the true wave vertical acceleration. The primary conclusion of this work is that the measured deck relative accelerations from a strapped-down, 1D accelerometer must be tilt corrected in environments of high wave heights.

The eye of Hurricane Katrina passed within 49 n mi of an oceanographic observing system buoy in the Mississippi Bight that is part of the Central Gulf of Mexico Ocean Observing System. Although a mechanical anemometer failed on the buoy during the hurricane, a two-axis sonic anemometer survived and provided a complete record of the hurricane’s passage. This is the first reported case of a sonic anemometer surviving a hurricane and reporting validated data, and it demonstrates that this type of anemometer is a viable alternative to the mechanical anemometers traditionally used in marine applications. The buoy pitch and roll record during the storm show the importance of compensating the anemometer records for winds oblique to the horizontal plane of the anemometers. This is made apparent in the comparison between the two wind records from the anemometers during the hurricane.

Oceanographic conditions in the Gulf of Mexico have been extensively studied from the summer of 1999 through the fall of 2000. These studies included cradle to grave surveys of Juggernaut Eddy; surveys in the Caribbean by several consortia; oceanographic surveys in support of hurricane research in the Gulf; measurements of inflow/outflow through the Yucatan Strait; and regional nowcasts and hindcasts of circulation. Several interesting phenomena have been observed during this period, including energetic bottom currents in excess of 2 knots and bottom furrows on the continental slope; the intrusion of one of the strongest eddies in a decade into the north-central Gulf leases; and strong midwater-column currents in SE Ewing Bank (~140 cm/s). This paper describes the observational data available and summarizes ongoing efforts to understand the oceanographic conditions during this period. Eventually, it is hoped that these efforts will lead to a better estimation of offshore structure design currents; an understanding of the dynamical causes of the strong mid-water-column currents; determining whether there is a link between the strong bottom currents at the base of the Sigsbee Escarpment and the Loop Current; and assessing the skill of the regional forecast/nowcast/hindcast oceanographic models.

The Texas Automated Buoy System operates buoys at seven sites off the Texas coast from Brownsville to Sabine in water depths ranging from ten to one hundred meters. The system is supported by the Texas General Land Office as part of its mission to mitigate the effect of catastrophic oil spills on the Texas Coast. Buoys communicate surface currents and water temperature measured at 2m depth in near real time via cell phone and commercial satellite digital data links. One buoy located at East Flower Garden Banks has a 300 kHz ADCP, a meteorology package with an ultrasonic acoustic wind velocity sensor, and a conductivity sensor. Data are posted regularly to a web page http://www.gerg.tamu.edu/tglo and are available to the public and governments within a few hours after data collection. On the TABS web page, a graphical map presentation of TABS current vectors has links to recent data tables and historical databases. Links are also provided to other data resources for oceanographic data in the Gulf of Mexico. Also on the web page are links to an automated continental shelf forecast system that predicts currents over the Texas-Louisiana shelf on an operational basis. There are four major components in this system: (1) forecast wind field retrieving and preparation, (2) shelf circulation model module, (3) simulation plotting module and (4) web display and file transfer module. The wind field used is a 3-hour interval ETA-22 forecast gridded wind from NOAA NCEP based on 00, 06, 12, and 18UTC model runs. The shelf circulation model is a 3-D version of Princeton Ocean Model (POM) on a domain extending from the coast to a curved line extending from 25 o N on the Mexican coast to 85 W at the coastline of Florida. The operational POM model used at this time is a simplified barotropic version that permits us to reduce computational time to allow prediction of surface currents twenty-four hours into the future. The data vs. model comparison from April through December, 1999 of nine nearshore TABS buoys indicates modest skill of the model in predicting the wind driven circulation. A fully baroclinic version of TABS-POM model is undergoing tests and will be implemented on an operational basis when sufficient computational resources become available. We are also developing data-assimilating models of the whole Gulf of Mexico and beyond to couple to our shelf model to supply outer boundary conditions.

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