Display screen or portion thereof with a transitional graphical user interface

[0001]FIG. 1 is a front perspective view of a display screen or portion thereof with a transitional graphical user interface, showing a first image in a sequence of our new design;

[0002]FIG. 2 is a front view thereof and is a first image in a sequence according to our new design;

[0003]FIG. 3 is a front view showing a second image thereof;

[0004]FIG. 4 is a front view showing a third image thereof;

[0005]FIG. 5 is a front view showing a fourth image thereof;

[0006]FIG. 6 is a front view showing a fifth image thereof;

[0007]FIG. 7 is a front view showing a sixth image thereof;

[0008]FIG. 8 is a front view showing a seventh image thereof;

[0009]FIG. 9 is a front view showing an eighth image thereof;

[0010]FIG. 10 is a front view showing a ninth image thereof;

[0011]FIG. 11 is a front view showing a tenth image thereof;

[0012]FIG. 12 is a front view showing an eleventh image thereof;

[0013]FIG. 13 is a front view showing a twelfth image thereof;

[0014]FIG. 14 is a front view showing a thirteenth image thereof;

[0015]FIG. 15 is a front view showing a fourteenth image thereof;

[0016]FIG. 16 is a front view showing a fifteenth image thereof; and,

[0017]FIG. 17 is a front view showing a sixteenth image thereof.

[0018]The inner broken line rectangle in the figures shows the display screen or portion thereof. Broken lines outside the display screen show the environment of a computing device. The remaining broken lines show portions of the graphical user interface. All broken lines form no part of the claimed design.

[0019]The design sequentially transitions between the images shown in FIGS. 2-17. The process or period in which one image transitions to another image forms no part of the claimed design.