VNAV is essentially just following barometric altimeter, which is susceptible to temperature error in both directions - low and high. Just as you would end up lower than true altitude in cold weather, you will end up higher than true altitude in warm weather, if no corrections are made.
The latter very often isn't recognised as a problem, because it doesn't reduce your obstacle clearance, so all is well, right? Well, no. Unless you are following an ILS, which produces a fixed angle glideslope in the sky, you will end up high or low in non-ISA weather, regardless of AFDS mode used (V/S, LVL CHG or VNAV), as all of them are following the barometric altimeter.
On an approach in hot weather, you will end up fair amount higher than on an ISA day, so seeing 3 whites is very common - if this is combined with an already steep approach (3.5 deg or higher), it could be quite a challenge to keep the approach stabilised within normal parameters. There are generally two ways of dealing with this:
- Use full flap for landing, which reduces your ground speed and in turn your rate of descent. You then have a more margin to 1000ft/min, which is typically the limit for stabilised approaches. Once you are visual, disconnect the autopilot, maintain -1000ft/min until you are established on PAPI. If airline allows, you could also brief a higher rate of descent to correct.
- Accept that you are on 3 whites, and maintain that approach angle until flare.