Display Screen or Portion Thereof with 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 transitional graphical user interface showing our new design according to a first embodiment;

FIG. 2 is a second image thereof;

FIG. 3 is a third image thereof;

FIG. 4 is a front view of a first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing our new design according to a second embodiment;

FIG. 5 is a second image thereof; and,

FIG. 6 is a third image thereof.

The outer perimeter illustrated by dashed broken lines in the drawings illustrates a display screen or portion thereof and forms no part of the claimed design. The dot-dash broken lines in the drawings define the boundaries of the claimed design and form no part of the claimed design. The remaining dashed broken lines in the drawings illustrate portions of the graphical user interface that form no part of the claimed design.

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

The lighter gray, darker gray, and black shading in the figures illustrates a contrast of appearance.