You can consult the marine weather forecast directly on the Météo France website :
Local forecast for Port Ajaccio Tino Rossi
Daily coastal forecast for Corsica
Corsica/Continent coastal forecast
You can also contact the Marine Weather service of Météo France on 3250 (section 3 for the marine forecast) or on 08 92 68 02 20 (section 3 for the marine forecast).
The Météorama internet site also proposes a page dedicated to Corsica with wind/temperature/wave forecasts : www.meteorama.fr/cote-corse/