Weather Ball Gen 3 mechanics

Afaik the 50 base power of Weather Ball increases to 100 while there is an active weather effect.

I was playing around with modding gen 3 and I was wandering how the calculation works.

Does it get a flat +50 power, or does it double its base power?

So, for example, if I modded the move to have 100 base power, would that become 150 or 200 with an active weather effect?