Molecular dynamics simulations of water pentamers were carried out using the semiempirical Parameterization Method 3 method to calculate the forces. Simulations were performed in the microcanonical ensemble, at several (average) vibrational temperatures. Three distinct transitions were observed in these systems, corresponding to the onset of phase coexistence and of two hydrogen bond rearrangements that were predicted by previous structural calculations. A detailed study of the high-temperature pentamer dynamics is presented, which clarifies the distinction between liquidlike behavior and simple structural rearrangements in these systems.