Hindcasts and Real-time Nowcast/Forecasts of Currents in the Gulf of Mexico
Authors: Kantha L. , Choi J.-K. , Leben R. , Cooper C. , Vogel M. , Feeney J. 
Published: October 2008

Abstract
Accurate real time estimates of the state of an oceanic regionare useful to many, including the offshore industry. The advent of precision altimetry, combined with the readily available remotely sensed data from altimeters and radiometers has made real-time oceanic nowcast/forecasts a reality, and realistic coupled ocean-atmosphere model simulations a possibility. The fact that such real-time capability was not on hand even a year ago testifies to the rapid advances made in this field in the past year or so, and to the unqualified success of the NASA TOPEX/Poseidon (T/P) altimetric mission. With Jason mission followon to T/P, it is likely that this capability will be available into the foreseeable future. Here, in this paper, we will present results of hindcasts and real-time nowcast/forecasts for the Gulf of Mexico, based on a comprehensive ocean model driven by numerical weather prediction (NWP) winds and assimilating multichannel sea surface temperature (MCSST) and altimetric sea surface height (SSH) anomalies. The examples discussed include eddy Aggie in 1995, eddies Deviant and El Dorado in 1997 and ongoing real-time high resolution nowcast/forecasts in 1998–99. These examples illustrate that there now exists a capability that could be of great potential utility to offshore operations in the Gulf, and by extension, elsewhere around the world.

Introduction
The current decade has seen enormous strides in our ability to observe and monitor the oceans. Advanced telemetering in-situ devices, such as PALACE floats, autonomous underwater vehicles (AUV) and long-term moorings, are providing us with the capability for intense but limited sampling of the oceans. On the other hand, satellite-borne sensors are giving us the ability to monitor continuously many surface properties over most of the global ocean. Of these, altimeters, radiometers and color sensors have proven especially useful. As is evident from the recent 1997-98 El Nino, the combined suite of satellite and in-situ sensors has been very helpful in interpreting and even forecasting the evolution of such important oceanic processes. Nevertheless, estimating and monitoring the state of the global ocean including its interior, requires appealing to comprehensive ocean models assimilating these in-situ and remotely sensed data, and it is here that we will see rapid advances in the coming decade.
Here, we provide an example of the hindcast/nowcast/forecast capabilities that ocean models and observing systems together are providing. The region is the Gulf of Mexico, from which nearly half of the US domestic oil is extracted, and where real-time nowcast/forecasts of currents in the water column are a valuable aid to the US offshore industry.

Model-based Ocean Monitoring & Forecast System
An important component of a numerical-model-based ocean monitoring and forecast system is the ocean model itself. The hope is that if properly done, dynamics will provide a means of interpolating and extrapolating observations temporally and spatially. The centerpiece of our nowcast/forecast system is a regional, relocatable, three-dimensional, primitive-equation-based, sigma-coordinate baroclinic circulation model, the CU version of Princeton Ocean Model1 (CUPOM). It includes free surface dynamics essential to littoral applications.