Ghana can be quite a formal country in business. I would wear a shirt and tie for the first day and then see how it goes (short sleeves are fine). Ghanaians do not expect westerners to wear a jacket, they understand how we sweat out there.

If you want to honour your Ghanaian colleagues then Friday wear is an important thing. It is traditional for people to wear African dress on a Friday in the office. Just pick up an African shirt when you arrive, this will be appreciated and of course makes you look like you understand the culture you are working in.

When are you going to Accra?