Where can I acquire global wind (speed and direction) data? Preferably in some kind of GIS format and free of charge.
windyty is non-commercial and in the menu tells you what open source libraries are used to create it. including noaa data
noaa climatic data (this is u.s. only, but i know they have it globally)
so if you dig around between the two you should find what you need.
the bonus from windyty is they also show you how you can display it
Not sure if you need a forecast or observations, assuming both, my recommendation will be.
Most common global forecast containing wind data is GFS by NCEP. You can see if it contains required wind variables and play with data values via free API at Planet OS Datahub.
For observational, historical global wind data, I'd suggest looking into CCMP Wind Vector Analysis Product V2.0 which is modelled from satellite and weather stations. It contains U & V vectors, so both, direction and scalar speed can be calculated. You can look at the dataset details at original source or inspect values via free API at Planet OS Datahub.
I would check out the Global Wind Atlas by the DTU Energy and the World Bank Group. They have global data in GIS format, free of charge. Hope this is helpful!
Although sailwx primarily purpose is to display maritime information, you may find some wind-related data (speed and direction) from weather stations in easy-to-crawl tables. I hope this will help you.
A few of my colleagues in the MELODIES project (www.melodiesproject.eu) are using open wind data from various European sources. I just asked them for their recommendations:
There are the brand new shiny Copernicus data sets
You can also get global re-analysis data from the European Centre for Medium-Range Weather Forecasting. The data come in GRIB/netCDF format which should be well-supported for conversion.