1. An automated method for simulating a trajectory for a vehicle in a 4d fluid current field comprising: (a) receiving, into an electronic computer, simulation objectives and a forecasted current speed; (b) initializing, in the electronic computer, a simulation time, a heading of the vehicle, an up/down flag, a current speed, vehicle motion of the vehicle, a dynamic compensation factor, a vehicle position of the vehicle, a horizontal speed of the vehicle, a vertical speed of the vehicle, and a vehicle depth of the vehicle; (c) updating the simulation time in the electronic computer; (d) interpolating, in the electronic computer, the current speed based on the updated simulation time, the vehicle depth, the vehicle position, and the forecasted current speed; (e) computing, in the electronic computer, the vehicle depth based on the updated simulation time, the up/down flag, the simulation objectives, and the vertical speed of the vehicle; (f) computing, in the electronic computer, the vehicle position based on the updated simulation time, the heading, the horizontal speed, the interpolated current speed, the dynamic compensation factor, and the simulation objectives; (g) if a threshold is met and the vehicle motion is not drift mode, updating, in the electronic computer, the simulation objectives; (h) computing, in the electronic computer, the dynamic compensation factor based on vehicle velocity of the vehicle, the vehicle position, an external position fix of the vehicle position, and an actual velocity of the vehicle; (i) computing, in the electronic computer, the trajectory based on the vehicle depth and the vehicle position; and (j) repeating, in the electronic computer, steps (c)-(j) until a termination factor has been met.