Large-scale atmospheric processes as well as small-scale ones determine the track of tropical cyclones in general. That's mostly valid over sea as interaction with terrain is too small to be integrated by global forecasting models (GFS, ECMWF, UKMET, etc.).

However, the atmosphere is a turbulent, chaotic, and complex system that even the best supercomputers will have a hard time simulating more than a day or more ahead. That's why you for every forecast a weather agency creates, a cone of uncertainty is always included because that's where you would find the center of the storm about 70% of the time, based on skilled model predictions, past forecasts, and other factors.

That's why no meteorologist will say to you that you should only look where the centerline of the forecast will be. The cone of uncertainty will give you a better picture where a storm is headed.

And also, once a storm is inland, land interaction will occlude its eye (more so when a storm is not a typhoon - there's no "eye" to speak of, only a spot where the bulk of convection is rotating -- and that's not always visible in visible-spectrum satellite images). That's where radar images come in handy when the storm has made landfall. More often than not, post-storm analysis is always done a few hours after the initial forecast. Several vortices may have been created during its track over land that it's very difficult to discern which rotating feature is the "eye" or "center of circulation". Even "big" and "more technologically-advanced" weather agencies (e.g., JMA, JTWC, NHC, UKMET) revise their forecast (and the center of the storm) hours after its initial analysis.

And PAGASA is the official weather agency of PH. They need to release a forecast now since they're the ones with the remit of informing the public of the weather conditions now and in the hours thereafter.