If you mean to counter the weather, they have the same speed, so all you need is a 0 IV and a -Spe nature (quiet is good; -Spe, +SpA). Only problem is that you can't hold any items to reduce speed, because you'll hold the blue orb, so when someone like me runs a quiet/brave Groudon with 0 Spe IV's, the weather condition will be randomly chosen. If this isn't what you were asking (because you have, like no description at all) then I've no clue what you asked in the first place. Then again, if you wan't to just be faster than Groundon, you might only need to be a modest nature or have a 31 Speed IV, you'll out-speed Groudon, and can hit with hp ground or earthquake. I'll do calcs, just for fun:
(Without Investment)
252+ SpA Kyogre-Primal Hidden Power Ground vs. 0 HP / 0 SpD Groudon-Primal: 202-238 (59.2 - 69.7%) -- guaranteed 2HKO
252+ Atk Kyogre-Primal Earthquake vs. 0 HP / 0 Def Groudon-Primal: 178-210 (52.1 - 61.5%) -- guaranteed 2HKO
(With full Def/SpD investment)
252+ SpA Kyogre-Primal Hidden Power Ground vs. 0 HP / 252 SpD Groudon-Primal: 158-186 (46.3 - 54.5%) -- 53.9% chance to 2HKO
252+ Atk Kyogre-Primal Earthquake vs. 0 HP / 252 Def Groudon-Primal: 150-178 (43.9 - 52.1%) -- 14.1% chance to 2HKO
I used smogon's calculator, here:
https://pokemonshowdown.com/damagecalc/index.html
