Display Screen or Portion Thereof with a Transitional Graphical User Interface

FIG. 1 is a view of a display screen or portion thereof with a transitional graphical user interface showing a first image in a sequence according to the claimed design;

FIG. 2 is a second image in the sequence thereof; and,

FIG. 3 is a third image in the sequence thereof.

The appearance of the transition is sequential from FIG. 1 through FIG. 3 .

The process or period in which an image transitions to another image forms no part of the claimed design.

The longer-incremented broken-lines showing a portion of an electronic device and the intermediate-length broken-lines showing of a display screen boundary, as well as the still shorter broken-lines showing unclaimed features, are included for the purpose of illustrating environmental structure and form no part of the claimed design. The boundaries shown for the electronic device and the display screen provide a context of the claimed design as being on an article of manufacture and are not intended to be limiting of a scale of the claimed design relative to the display screen.