Festuca hawaiiensis is a cespitose (growing in tufts or clumps) annual with numerous erect culms (stems, stalks) 0.5 to 1.5 m (1.6 to 5 ft) tall, branching somewhat above the base, and glabrous to slightly puberulent. Sheaths are open and blades flat and smooth, 25 to 40 cm (10 to 16 in) long, and 3 to 12 mm (0.12 to 0.5 in) wide. Inflorescences are paniculate, composed of six to eight alternate racemes, with a flattened rachis, and are puberulent and winged. The fruits are ellipsoid, dorsally compressed, and 1.5 to 5 mm (0.06 to 0.2 in) long.