Normally I see thunderstorms to have an updraft and a downdraught.

Here is my question, do the storms in the afternoon on a warm humid day need a downdraught or dose the whole cloud rain?

Thunderstorms always have updrafts and downdrafts. Those on warm, humid days are almost always of the thunderhead type. Simple rain storms don't have to have updrafts.

You might find this Wiki input of interest. Microburst - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Microburst)

It appears that the rain can be causal for the downdrafts.

I suspect that there is still much not understood about thunderstorms, however.

Well, initially the storms only have updrafts and no downdrafts, when they're developing. However when the storms have reached full maturity, they have both updrafts and downdrafts.