SN 16 day forecasts and WAMs

Hi Carpetman, yes, you are correct that currently ww3 only provides forecasts out to +180 hours.

In my previous post in this forum I asked if the forecasts were based off the NOAA WW3 model forecasts or not, and Ben said they using an in-house ww3 model.

So based on that, I am guessing they are running their own version of ww3 (which is a freely available model) and running it using the NCEP 16 days GFS weather model forecasts.

You can see an example of the 16 day GFS here http://www.weatherzone.com.au/models/?lt=wzcountry&lc=aus&mt=mrf . You will need to register a "pro" account, which you can a free one month trial for, and then click on the US 16-Day link.

From memory, the 16-Day GFS is essentially the same model used to drive the 10-Day WW3 forecasts, but just run for longer. It may have a slightly lower model grid resolution, but I am unsure off the top of my head.

Yip correct again. The NOAA WW3 forecasts are based upon satellite altimeter and wave buoy (and most likely a few other sources) data to determine the present sea state. The ww3 model then forecasts the growth, transformation and decay of waves due to a number of processes such as wind forcing (from GFS) and effects due to the ocean floor such as diffraction, shoaling friction etc...

carpetman wrote:

I thought GFS was a completely different model putting out wind, pressure data etc. not wave data. But maybe the WW3 model is run on the GFS model? Anyway, my question has been answered. Thanks.

You got it - WW3 based on T384 GFS input data.

Kiwi123 wrote:

The NOAA WW3 forecasts are based upon satellite altimeter and wave buoy (and most likely a few other sources) data to determine the present sea state.

Not quite. Altimeter and buoy data is only used for verification. The WW3 model runs independently on GCM wind forcing, and creates a self-initialised restart file every model run which is then used to kick off the next run.

e wrote:

Not quite. Altimeter and buoy data is only used for verification. The WW3 model runs independently on GCM wind forcing, and creates a self-initialised restart file every model run which is then used to kick off the next run.

I knew that it runs independently.

Ahhh thanks, it has been awhile since I last looked at the specifics.
So the initial conditions do not necessarily represent the actual global wave conditions at T+0 ?
What do you mean a self-initialised restart file?

Kiwi123 wrote:

So the initial conditions do not necessarily represent the actual global wave conditions at T+0 ? What do you mean a self-initialised restart file?

Yeah, initial conditions may not always be right (and that's where a lot of 'errors' in wave model forecasts originate from - poor analysis/initialisation). Where would they get wave data in the deep Southern Ocean from?

Re: self-initialised restart file - it may not be the proper technical term but what it means is that the model uses its own forecast data to create the next 'analysis' timestep. So if you're running the model every six hours, it'll use T+6 as the next run's 'analysis' data (which itself is the previous analysis time step plus six hours of wind forcing).

Thanks for the reply. Ahhh, ok, so it is essentially using a previous forecast as the initial conditions.

I guess I was over-estimating the instantaneous global coverage of wave buoy and altimeter data.

Thanks

Yeah there's lots of buoy coverage in the Northern Hemisphere (particularly around North America and Hawaii due to to NOAA's incredible buoy program) but there's very little coverage in the Southern Hemisphere. And most buoys are typically located close to the coast and are therefore attenuated by local bathymetry, which makes it a little harder to quantify the accuracy of the wave models.

Ben, up until earlier this year, didn't the Jason 1 Altimetry provide a way of calibrating modelled wave height versus actual wave heights?

It does provide some verification input ('assimilation') - as does ENVISAT - but the satellite tracks are very narrow and don't cover much ocean.