If counties with almost all their vote in shifted ~3 points left vs. 2018, we might expect future counties to do so too.
We can then apply margin estimates to turnout estimates and add everything up.
My turnout baseline is 76% statewide (10.976M), but that might be adjusted.
I chose the 2018 gubernatorial race rather than the 2016 presidential race as the baseline comparison for Florida counties because it does seem from the polling that Trump may outperform his 2016 margins with Latinos. The midterm elections showed a similar demographic pattern.