What is TDI SeaState and how is it generated?.

TDI SeaState is a weather forecast and climatology system that was designed and built by Dr. Les Bender. Dr. Bender came to TDI-Brooks in 2010 with extensive experience in operational meteorology and oceanography. He saw the need for an in-house weather product that focused on providing real-time and climatological sea state information specifically tailored to TDI’s operations at sea. The web page is not visually impressive; it was not meant to be. It was designed to convey the weather information needed to make daily and long-term operational decisions in a compact format that only required a limited satellite bandwidth, i.e., there are no ads or click-through’s..

The information presented in TDI SeaState is not provided by a professional third party source, but is downloaded directly from the data made available by NOAA's National Centers for Environmental Prediction (NCEP). This is the same source as used by popular weather apps such as Windy, Weather Underground, AccuWeather, WeatherBug, the Weather Channel, etc. The foundational tenet is simple; the National Weather Service, the National Hurricane Center, NOAA, and NCEP will always do a better job than a commercialized operation because they have the resources, the people, the weather stations, the weather buoys, the budget, and the advanced numerical models and computing resources that private industry could not duplicate.

There are three major components to TDI SeaState:

• Waves and Winds
• Ocean
• Atmosphere

Waves and Winds: The operational wave and wind forecasts use the NCEP/EMC global deterministic wave model unified with the Global Forecast System (GFS). The WAVEWATCH III spectral wave model is one way coupled to the atmospheric forecast model. In addition, surface ocean currents from the Global Real-Time Ocean Forecast System (RTOFS) are input to the wave model. The model is run by NCEP four times a day: 00Z, 06Z, 12Z, and 18Z and produces hourly forecasts out to 120 hours and every 3 hours from 120 to 384 hrs (5-16 days). There are three native computational grids, one for the arctic, one for one for the northern hemisphere (15S to 52.5N), and one for the southern hemisphere (10.5S to 79.5S) and four post-processed grids.

The operational accuracy - forecasted wave heights within 1.5 foot (0.45 m) of the actual wave height recorded by a wave buoy - is typically excellent out to 3 days, good at 3 - 5 days, poor from 5 - 7 days, and statistical noise for any forecast longer than 7 days. Forcasting any weather conditions more than seven days out is usually fruitless. A comparison of wave forecasts compared to NDBC wave buoy data can be seen Wave Model Validation

There is an option to enhance the wave forecasts with an embeded, localized SWAN wave model to handle shallow-water bathymetry and small island shadowing effects that are not resolved with the higher resolution WaveWatch III model. This option must be requested.

Ocean: The operational ocean current, temperature and salinity forecasts use (RTOFS). RTOFS is based on an eddy resolving 1/12 degree global HYCOM (Hybrid Coordinates Ocean Model) that serves as the backbone of the National Weather Service's operational ocean system. The model runs once a day and produces a nowcast and eight days of forecasts. There is a single computational grid for the globe. As of 13 September 2024 the straigthforward means of obtaining vertical profile data was terminated; only the surface is readily accessible.

Atmosphere: The operational atmospheric forecasts use the Global Forecast System (GFS). The entire globe is covered by the GFS at a base horizontal resolution of 28 km. The model is run by NCEP four times a day: 00Z, 06Z, 12Z, and 18Z.  Each run produces forecasts of every 3 hours from the initial time out to 16 days. 

In addition to the three major components there are a number of additional components:

• Sea Level
• Sound Speed
• Absorption Coefficients
• Weather Resources
• Bathymetry

Sea Level: The sea level tidal height variations and transports are generated with the OSU TXPO Tide Models. TXPO is a series of fully global models of ocean tides, which best fits, in a least squares sense, the Laplace Tidal Equations and satellite altimetry data.

Sound Speed: The sound speed profile is generated from the Chen & Milero model (1977) using the salinity and temperature profiles extracted from RTOFS. The temperature from the RTOFs model is potential temperature relative to the surface. Therefore in order to compare to actual sound speed profiles calculated from CTD profiles, which obviously are not using potential temperature, the model potential temperature is first converted to the insitu temperature. Pressures are converted to depth in metres using Leroy & Parthiot (1998). If needed, sound speed profiles can also be generated using the models of Del Grosso (1974) as modified by Wong & Zhu (1995), Fofonoff & Millard (1983), Mackenzie (1981), Wilson (1960) and the Thermodynamic Equation of SeaWater 2010 (TEOS10).

Absorption Coefficient: The absorption coefficient profile is calculated from the Absorption Coefficient Model (Kongsberg, 2007) using the salinity profile and the insitu temperature profile used for the sound speed, the sound speed profile itself (see above) and a default value of the ocean pH as 8.00. There is ongoing work to utilize the Global Ocean Biogeochemistry Analysis and Forecast model run each day by the Copernicus Marine Service to obtain a pH profile. The value of the absorption coefficient as a function of depth for a range of frequencies can be found in the downloadable csv file by clicking on the "Data" tab under Sound Speed & Absorption Coefficient.

Weather Resources: A link to additional weather resources such as visible satellite images, radar images, frontal analysis, and nearby NDBC wave buoys.

Bathymetry: Finally, there is an option to show the bathymetry from available DEM models, ETOPO1, GEBCO30, GEBCO 2019, SRTM15, and GMRT, as well as the (coarse) bathymetry of the RTOFS model. This option must be requested.

References:
Chen C.T., Millero F.J. (1977). Speed of sound in seawater at high pressures. J. Acoust. Soc. Am, 62(5), 1129-1135.
Del Grosso, V.A. (1974). New equation for the speed of sound in natural waters. J. Acoust. Soc. Am, 56(4), 1084 - 1091.
Fofonoff, P. and Millard, R.C. Jr. (1983). Algorithms for computation of fundamental properties of seawater, Unesco Tech. Pap. in Mar. Sci., No. 44, 53 pp.
Kongsberg, (2007). SIS Operator Manual, Rev. F, Technical Reference, Section 7.16
K.V. Mackenzie, K.V. (1981). Nine-term equation for the sound speed in the oceans. J. Acoust. Soc. Am. 70(3), pp 807-812.
Leroy, C.C. & F Parthiot (1998). Depth-pressure relationship in the oceans and seas. J. Acoust. Soc. Am. 103(3) pp 1346-1352.
Wilson W. D. (1960). Equation for the speed of sound in sea water. J. Acoust. Soc. Amer., 32(10), p. 1357.