Just in from SDOT:

Both of these are because of paving work, according to the SDOT advisory from which these excerpts are taken:

25th Avenue SW and SW Trenton Street
SDOT crews will work Saturday on 25th Avenue Southwest at Southwest
Trenton Street starting at 9 a.m. Northbound traffic on 25th will be
detoured at SW Henderson to 24th Avenue SW and returned to 25th at SW
Trenton until 3 p.m. on Saturday. After 3 p.m. only the northbound curb
lane on 25th will remain closed, and this lane will be opened by 5 a.m.
on Sunday, to allow time for the pavement to cure.

Southbound SR99
Two southbound lanes on State Route 99 between S Lander and S Hanford
streets will be closed on Saturday from 6 a.m. until no later than 6
a.m. on Sunday, to allow time for pavement to cure.