Sri Lanka Ocean Weather Forecast
Numerical model ROMS (Regional Ocean Modelling System) is a 3D, free-surface oceanographic model discretized with a terrain-following vertical coordinate system (class of sigma-coordinate models). It solves the Navier-Stokes equation with Boussinesq approximation and fluid incompressibility assumption. The model has been widely applied in many applications ranging from planetary scales down to the scales of estuarine environments. Besides calculations of water temperature, ocean currents, salinity, and sea surface height, it uses an advanced turbulence closure scheme describing sub-grid processes and enabling applications such as sediment transport modeling, etc.
Lateral boundary conditions for the outer ROMS model are daily updated from the global HYCOM model forecasts. Atmospheric forcing in our current ROMS setup uses outputs from our local WRF-ARW model output fields. Our model setup covers the Sri Lanka region at 2 km horizontal resolution. We archive our variables hourly, however, for certain locations even more frequent outputs are provided (10-minute outputs).
A list of ROMS model output parameters is provided on the Coastal Oceanography website:
Surface currents: surface currents velocity (m/s) and direction are shown with vector (arrow). The unit vector length is shown on the map legend. Current velocities less than 5 cm/s are not plotted. Colors under the vectors represent Sea Surface Temperature (°C).
Sea temperature: represents surface temperature defined in degrees Celsius (°C).
The Weather Research and Forecast model has been designed for operational forecast and atmospheric research, developed by NCAR (The National Centre for Atmospheric Research, USA). The scope of this model is wide, from the study of meteorological phenomena (convection, baroclinic waves, etc.) to the operational mesoscale forecasts and regional atmospheric circulation of the order of hundred meters to several thousand kilometres. The advantage of the meteorological model is that it allows the calculation of the value of meteorological parameters at the entire modeling area, including those places where there are no measurements.
WRF-ARW boundary and initial conditions are interpolated from GFS (0.25 degrees) global model results. Our setup covers the Sri Lanka region at a horizontal resolution of 4km. Model outputs are used as a forcing input for our ROMS ocean model. For certain locations, we save model outputs more frequently in time (actually at each model time step – 60s for big domain and 12s for nested). Those variables are presented in the Timeseries section.
A list of WRF model output parameters is provided on the Coastal Oceanography website:
Air temperature: the value is given in °C and refers to the temperature 2m above ground.
Pressure: Mean Sea Level Pressure given in hPa.
Wind: wind speed (m/s) and direction at 10m height.
Precipitation: Given in millimetres and represents the accumulated total precipitation for the last 3 hours.
Reflectivity: a reflectivity of the atmosphere measured in dBZ. The most common value for convective cloudiness reflexivity is above 35 dBZ. The higher the dBZ value, the stronger the convective processes (which may later lead to precipitation).
MCAPE: Mean Available Convective Potential Energy (CAPE) is one of the measures of tropospheric instability. Generally, the higher the MCAPE value, the greater the probability of development of thunderstorms.