This article is from the Storms FAQ, by Chris Landsea firstname.lastname@example.org with numerous contributions by others.
A "TUTT" is a Tropical Upper Tropospheric Trough. A TUTT low is a TUTT
that has completely cut-off. TUTT lows are more commonly known in the
Western Hemisphere as an "upper cold low". TUTTs are different than mid-
latitude troughs in that they are maintained by subsidence warming near the
tropopause which balances radiational cooling. TUTTs are important for
tropical cyclone forecasting as they can force large amounts of harmful
vertical wind shear over tropical disturbances and tropical cyclones. There
are also suggestions that TUTTs can assist tropical cyclone genesis and
intensification by providing additional forced ascent near the storm center
and/or by allowing for an efficient outflow channel in the upper troposphere.
For a more detailed discussion on TUTTs see the article by Fitzpatrick et al.