Hi. I´m one of those skippers mentioned by svlamorocha. From Cape Verde
to Salvador, any month of the year is good, not big changes in weather/wind. I do recommend to stop in Fernando de Noronha Island, easy to clear in (Policia Federal and Capitania dos portos) and beautiful island. From Salvador to Rio, better avoid winter months, July, August, but even so the fronts coming from south are normally not so strong, and you have some harbours all the way to stop and get shelter in case there are one front approaching to wait then to pass.
From Rio to Punta del Leste, Uruguay, the same, avoid winter, but fronts are stronger as you go south, and you have less ports
to get shelter.
From Rio to Punta del Leste (the most south that I went), the wind
patern is NE, E, SE and with the front approaching, NW, then W, SW and S , the front itself. I´m from Rio and have done that several times...