Lagrangian simulations:
Trajectories were initiated from a regular grid of initial positions with a constant spacing of 0.01 degrees within a polygon encompassing the Campeche pool of cool water as determined from satellite SST on July 19, 2018 (Fig. \ref{581122}). Back-in-time trajectories indicate that the water within the polygon of initial positions mainly came from the northeast in the 2018 experiment, and only from the northeast in the climatological experiment.
Using the 2018 velocity, about 18% of all trajectories had at least one longitude to the west of the westernmost point of the initial-position polygon, and 80% of all trajectories had at least one point to the east of the easternmost point of the initial-position polygon (Fig. \ref{581122}b). In the climatological experiment, in contrast, trajectories only from the Yucatan shelf to the northeast (Fig. \ref{581122}d).
At the surface, SST advection by the ocean model (HyCOM) also shows cool water moving along the same path as the trajectories and along a tongue of water that is about 2–3 degrees Celsius cooler than the rest of the surface water over the Yucatan shelf (Fig. \ref{581122}c). Satellite and model SST are in good agreement, although the model has additional variability as should be expected from a higher resolution simulation (Fig. \ref{581122}a and \ref{581122}c).