Display screen or portion thereof with transitional graphical user interface

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

FIG. 2 is a front view showing a second image of the first embodiment;

FIG. 3 is a front view of a first image in a second embodiment of the claimed design; and,

FIG. 4 is a front view showing a second image of the second embodiment.

The dynamic graphical user interface has transitions between certain ones of the figures. The appearance of the transition is sequential from FIG. 1 to FIG. 2 in the first embodiment and from FIG. 3 to FIG. 4 in the second embodiment. The process or period in which an image transitions to another image forms no part of the claimed design.

The thick, dashed hexagon shown in FIGS. 1-2 and FIGS. 3-4 portrays environmental structure and forms no part of the claimed design.

The longer-length broken-line showing of a display screen and the intermediate-length broken-line showing of a display screen boundary, are included for the purpose of illustrating environmental structure and form no part of the claimed design. The remaining broken lines show elements of the graphical user interface that form no part of the claimed design.