Engineering of synthetic magnetic flux in Bose-Einstein condensates [Lin et al., Nature (London) 462, 628 (2009)] has prospects for attaining the high vortex densities necessary to emulate the fractional quantum Hall effect. We analytically establish the hydrodynamical behavior of a condensate in a uniform synthetic magnetic field, including its density and velocity profile. Importantly, we find that the onset of vortex nucleation observed experimentally corresponds to a dynamical instability in the hydrodynamical solutions and reveal other routes to instability and anticipated vortex nucleation.One of the driving forces behind quantum degenerate gas research is the emulation of many-body condensed matter phenomenon [1]. For quantum degenerate Bose gases, achievements include the observation of Bloch oscillations [2] and the Mott insulator superfluid transition [3]. Considerable attention has also been applied to the achievement of the fractional quantum Hall (FQH) regime in rotating Bose-Einstein condensates (BECs) [4]. To obtain quantum Hall physics time reversal symmetry must be broken. In solid state devices this is done through the relatively simple process of applying a magnetic field. Since the atoms in a BEC are neutral an alternative method needs to be applied to break time reversal symmetry. In the context of FQH physics considerable focus has been applied to the breaking of time reversal symmetry through rotation.For BECs in rotating traps the nucleation of vortices has been observed by several groups [5]. Theoretical superfluid hydrodynamical studies, in the Thomas-Fermi (TF) regime, have proved effective in calculating the rotation frequency at which vortices are nucleated by dynamical instability [6,7]. Such studies, which have been extended to dipolar BECs [8], agree with numerical predictions from the Gross-Pitaevskii equation [6,7,[9][10][11][12]. However, to reach the FQH regime the number of vortices needs to be significantly larger than the number of bosons in the BEC. Typically, experiments are carried out in parabolic traps, defined by average in-plane trapping frequency ω ⊥ . When the rotation frequency, z , is equal to ω ⊥ the BEC becomes untrapped. Hence, the attainment of the FQH regime, which requires z → ω ⊥ , is an extremely challenging task. An alternative approach is to generate a synthetic vector potential [13], which breaks the time reversal symmetry of the problem, producing a synthetic magnetic field [14][15][16][17][18][19][20].The recent work of Lin et al.[20] has demonstrated the effectiveness of such an approach, in a 87 Rb BEC, through the experimental realization of a synthetic vector potential in the Landau gauge: A * = A * xX , corresponding to a synthetic magnetic field B * = ∇ × A * . The authors showed that vortices were nucleated at a critical synthetic magnetic field. Here we generalize the TF methodology used to successfully calculate the onset of vortex nucleation in rotating systems [6,7] to the case of synthetic magnetic fields in harmonically confined BECs. W...