The PredictWind weather routing is the best way to get the most accurate forecast data for your trip. The data size is very small, so ideal for Satellite & SSB connections.
The weather routing shows the results from 6 forecasts:
ECMWF (Black) ECMWF is the number one ranked global mode from a national weather agency, 9 km resolution globally.
Spire (Orange) Spire is the #1 ranked global model from a private weather company, often outperforming ECMWF in the open ocean, 25 km resolution globally.
UKMO (Yellow) UKMO is the number 2 ranked global model from a National weather service. A very highly regarded model, 15 km resolution globally.
PWG (Blue) stands for the PredictWind weather model that uses the NCEP global initial conditions for the model run. Resolution available is 1km/8km/50km global.
PWE (Red) is the PredictWind weather model that uses the European Center for Medium Range Weather Forecasts global initial conditions. Resolution available is 1km/8km/50km global.
GFS (Green) Global Forecast System from NCEP as this is used by most other weather websites/apps - 25 km resolution globally.
NOTE: The weather routing or departure planning will always use the highest resolution (1km,8km,15km, 25km,50km) and most accurate GRIB files available. As the weather routing or departure planning is calculated on the PredictWind server, it is not dependent on what GRIB files you have downloaded, making the weather routing file size small, typically 5-9kb. The GRIB files are only used to visualize the routing.
This multiple forecast approach is called 'Ensemble' forecasting, where you can have a high degree of confidence if all forecasts are similar. If there is a spread in the forecasts and optimal routes, it shows the uncertainty in the forecast.
Here are some tips for interpreting the results:
If you are looking at a 'coastal' route, the PWG/PWE forecasts are at 1km (Professional Package) or 8km resolution (Standard Package) and will model the geographic/heating effects. The 9km ECMWF, 15km UKMO, will pick up some of these effects but not as accurately.
For short term decision making you should select the forecast that appears to be doing the 'best job' of matching the observations. You can use your boat data, and data from the observations page in PredictWind.
In addition, try to understand if there is a clear reason that the routing is going a particular direction i.e. is it due to wind direction or strength. Please watch the animation carefully. The weather routing is not an exact road map to follow but a general trend, as the timing and placement of the weather pattern is never 100% accurate.
If there is a lot of uncertainty the routes will be spread out, and it may be best to simply sail the fastest VMC along the course. But generally the routes should line up for the first 12-24 hrs. You should be updating the route with each new forecast every 12hrs. To check when the forecast updates please see the FAQ
The routing algorithm will find the best route based on your polar and the forecast. It looks at ALL the possible paths and selects the best route. However, it is only as good as the forecast, and the accuracy of your polar. The forecast is an average over 1 hour, but the forecast at the lower resolutions 8km & 50km are only output every 3 hours. So, the optimum route does not have the granularity to help with short term wind shifts, and variations in wind speed. So, it is important you decide on how best to use the short-term gains over a 3-hour period. We recommend treating the optimal route as a general guide, and fine tune it for the exact conditions you experience.
Please note, the forecast will run for a maximum of 14 days. Beyond 14 days, the model forecast is not accurate.
The optimal route is only as accurate as the forecast, and the polar you have setup. Please ensure you have correctly set up the polar, and the boat speeds shown in the results match your actual boat speeds.
See below the wind angles we use to define upwind/reaching/downwind.
% time upwind = True Wind Angle is 55 degrees or less.
% time reaching = True Wind Angle is between 55 degrees and 135 degrees.
% time downwind = True Wind Angle is 135 degrees or more.