occasional

convulsive, sudden, violent

broken, disconnected, fragmentary, interrupted

aimless, arbitrary, desultory, haphazard, hit-and-miss, hit-or-miss, odd, random, scattered, slapdash, stray

capricious, changeful, changing, flickery, fluctuating, fluid, inconstant, mercurial, mutable, temperamental, uncertain, unpredictable, unsettled, unstable, varying, wavering

changeable, fickle, variable, volatile

scarce, scattered, uncommon, unique, unusual

choppy, discontinuous, erratic, fitful, intermittent, irregular, spasmodic, spotty, unsteady