vorcity, kavadude, you got it! Moist (but not wet since that leads to root rot eventually) weather at lower elevation in warm climates is ideal.
Chris, we tried growing Kava at higher elevations on the big Island and the results were pretty dismal due to the incredible amount of rainfall (leaves would get pale green as they were literally stripped by the rain), and over the years, we noticed a big difference between plant yield from near sea level to higher elevation.
Kava loves lower elevations was the conclusion of that experiment.
Kavadude, one of my favorite things in the world is coming home early evening, digging up a medium sized kava plant, cleaning it, pounding the roots and making fresh kava beverage a few hours later. Average yield depends on the care and soil. A friend harvested a record 70 pounds of root from a 5 year old plant. It was a erect growing variety like Spotted Hiwa or Nene (not a prostrate grower like Papa 'Ele 'Ele which never yields as much, but is still my personal favorite Hawaiian variety.)
This yield speaks volumes about soil quality since 2+ year old plants sometimes develop nematodes and the little critters make homes inside the lateral roots.
In a perfect world, I'd have staggered growth of the various varieties I love. Continuous planting and TLC

Cheers to a freezer full of Kava pulp!
AG