Ten days and then again a week before our trip earleir this month rain was predicted almost every day. It varied back and forth -- all days, a few days, most days -- until we left, then it was supposed to rain one day for sure, others a low chance.
NO rain, none, for five days, not a drop after midnight the evening we arrived (It was pouring when we arrived at 5:30 pm but who cares. We were at AKL and ate at Boma.) Gorgeous weather the whole time.
You never know. Burden yourself with the ponchos and mini-umbrellas to improve your odds of not needing them!