I feel for the people of Puerto Rico. For updated tracks click here.
The critical turn should occur on days 4 and 5 from now. That is around Sunday September 24th. We'll be watching closely to witness the turn. Basically, the turn is supposed to occur between two ridges. This is different from Irma, mainly due to the size of the ridges. Irma had a very small low to pull it along it's path. Maria is going to be sandwiched between two significant bodies of air.
We will have to wait and see how she behaves.