A TUTT lo is an Tropical Upper Tropospheric Trough that is at 250 - 500 mb. How that differs from an ULL I frankly don't remember right now. Whether its higher or lower in elevation, or if it is positioned between two high pressure area and somewhat anchored may be the key. Someone on this board should have a quick answer. The short of it is that they seem to be very reluctant to move anywhere fast and can act as a buzzsaw to tropical disturbances/Storms. Interesting to note today that the TUTT low currently in the Caribbean is split into two areas; one in the Bahamas and one in the eastern GOM. The one in the Bahamas is expected to move north as the trough coming into the SE moves in. That may leave an opportunity for the wave near Haiti/DR to develop as it gets in the western caribbean. Long shot, but possible. Anyhow, now that I haven't answered your question at all, I'll leave to the experts here. Cheers!!