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 sequence according to a first embodiment of the claimed design;

FIG. 2 is a front view showing a second image in the first sequence according to the first embodiment of the claimed design;

FIG. 3 is a front view showing a third image in the first sequence according to the first embodiment of the claimed design;

FIG. 4 is a front view of a first image in a second sequence according to a second embodiment of the claimed design;

FIG. 5 is a front view of a second image in the second sequence according to the second embodiment of the claimed design;

FIG. 6 is a front view of a third image in the second sequence according to the second embodiment of the claimed design;

FIG. 7 is a front view of a first image in a third sequence according to a third embodiment of the claimed design;

FIG. 8 is a front view of a second image in the third sequence according to the third embodiment of the claimed design; and,

FIG. 9 is a front view of a third image in the third sequence according to the third embodiment of the claimed design.

The appearance of the image transitions sequentially between the images shown in FIGS. 1-3 ; FIGS. 4-6 ; and FIGS. 7-9 . The process or period in which one image transitions to another image forms no part of the claimed design.

The shading depicts a contrast in appearance.

The outermost long-dash broken lines illustrate an electronic device, which is the environment of the design, and form no part of the claim. The remaining broken lines illustrate portions of the display screen and portions of the graphical user interface that form no part of the claimed design.