Apart from the element of uncertainty, the other thing is the slow pace of the typhoon due to the lack of a strong steering influence - and it may even slow down more than they are predicting. (Spoke to an avid chaser at Sugar today and he thinks a loop is even possible.) This makes it a potentially very dangerous typhoon as it takes longer to pass and historically, slow moving typhoons of about this strength have been the most destructive (Marakot, Nari). Will be an interesting one to watch.

Chart shows the high well north of the typhoon resulting in a reduction of the high's steering influence. However, the low pressure to the north of Saola, being much closer to the high can more confidently be predicted to follow the contoured ridge of the high and at a much faster pace.

Meanwhile the low behind Saola to the east would have to be an excellent chance to develop as well.