The main wind season is between May and October. During sunny days, and especially in summer, strong thermal winds blow from the north/northwest. This type of wind is called Nortada, and its literal translation is “Strong North Wind.”
If you are into wave surfing, you will for sure want to check the swells.
Ideally you will want to look for swells with a periodicity of 15 or more.
The first popular wave forecast site is Surf-forecast.
And the second is Magicseaweed which also has webcams along with nearby sports information. This is probably the best choice.
Of course you will want to check the wind forecast to plan a kitesurf session. It is important to underline that wind forecasts are mathematical models which do not factor in local features and phenomenons such as venturi wind acceleration on cliffs or thermic effects. The Portuguese cost was built by erosion and is full of cliffs, many spots have stronger winds then forecasted, for example Guincho. Also some areas strongly benefit of thermic effects during the summer, for example Alcochete.
You can look for side-on conditions of 12 knots and above, note that in the north of Portugal you can usually add 2-6 knots to the forecast.
Of course the world standard for wind forecasting is Windguru
Windguru also provides swell forecasting, which can be a good all-in-one option.
Some spots have local weather stations open to public access. Those enable you to check live conditions.
For example Praia de Leça is just nearby the port of Porto, you can check the weather station of Porto de Leixões.
There is a Windguru live station indicating wind conditions in Praia do Guincho: station 2762.
There is a Windguru live station indicating wind conditions in Fonte da Telha: station 464.
Tides are key to planning sessions in some spots.
For example in Alcochete, Praia dos Moinhos, is a fluvial beach subject to the tides of the Tagus river. You must ride there by high tide, it is not possible to ride by low tide. But the tidal coefficient is important, for example in Alcochete it is better to go out with more a high coefficient or the water will be very muddy.
Or in Lagoa de Óbidos, as well, it is not possible to ride by low tide.
We recommend to check the Tábua de marés.
Portugal has many webcams installed along the coast and are available to check what is happening on the beaches.
The most comprehensive set of live webcams is available on Meo Beachcam.