I would say 3, but in fact, it has at least a dozen climatic zones.
The three principal climatic zones are:
1) The tropical lowlands of the Caribbean region, wich are hot and humid
2) The interior uplands of the ishtmus, where the temperature climate is cool and damp in the valleys and plateaux, to cold in the mountains.
3) The lower Pacific slope and coastal plains, wich have hot and dry conditions