He's not on his way to Emond's Field at all. Once he reached the Jehannah road Perrin planned to go east toward the Molvaine Gap.
Something made him change his plans. At some point during the TGS timeline he has retreated a few leagues beyond the border of Ghealdan, where he is camped. Galad is apparently with him, or meeting with him. That's where Perrin was when Cadsuane/Nynaeve fetched Tam.

Galad is considered a deserter to be hunted down and Tylee in KOD spotted his position. The Seanchan had armies watching Murandy in the Molvaine Gap. It's pretty obvious Galad found his way east blocked, and it's possibly when he figured that out and made a u-turn and headed back toward Ghealdan that he bumped into Perrin. What is more mysterious is why isn't Perrin using Travelling, why go camp beyond the border of Ghealdan (as if he were hiding from the Seanchan) instead of using gateways to go straight into, for instance, Andor. The Asha'man should be rested by the end of TGS. Even if the Asha'man are too busy sending small groups of refugees home, it doesn't make much sense not to move everyone to a safer place like Andor before starting to send people home. Has Perrin sent the Asha'man on some sort of mission and they have not returned? Did someone came for them (eg: Taim, Logain, Rand himself). We know there's been contact at some level between people with Rand and people with Perrin, because Maidens who were with Perrin were suddenly with Rand again in TGS, and Rand/Min showed no surprise about that fact, so apparently they knew what was up with that. We know the WO were there to deal with Masema, so possibly they went their own way after his death. They could not Travel (the WO learned the weavet after their departure), but the Dreamwalkers (all with Rand) could walk their dreams and locate them.

ToM is going to tell us what happened, but by the end of TGS Perrin wasn't on his way to Emond's Field. It sounds like Perrin got stalled again, but that a lot of fairly unforeseen developments have taken place in his story line during TGS (beside the obvious one: meeting Galad).