Display screen or portion thereof with a transitional graphical user interface

FIG. 1 is a front view of a first image in a sequence for a display screen or portion thereof with a transitional graphical user interface;

FIG. 2 is a front view of a second image thereof;

FIG. 3 is a front view of a third image thereof;

FIG. 4 is a front view of a fourth image thereof; and,

FIG. 5 is a front view of a fifth image thereof.

The broken lines showing the display screen and the remainder of the graphical user interface forms no part of the claimed design. The outer shape in broken lines of an example device forms no part of the claimed design. The transitional graphical user interface shown in broken lines forms no part of the claimed design.

The subject matter of this patent includes a process or period in which an image sequentially transitions into another image. This process or period forms no part of the claimed design.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-5 .