Mateus 14:23-24

After dismissing the crowd, Jesus walked up the mountainside (NIV) to pray. There are no real mountains in this part of the Galilee coastline, but there are hills that slope down to the lake. He evidently stayed there longer than He had led the disciples to conclude that He would. Perhaps He prayed about the crowd’s attempts to make Him king (John 6:15) among other things.

The word "evening," as the Jews used it, covers a period from late afternoon to shortly after sunset (cf. Matthew 14:15). Obviously it was now late in that evening period. By this time the boat the disciples were in was out quite a distance from the shore (Matthew 14:24). A storm had arisen and the winds were blowing from the west and evidently forcing them away from the northern shore, impeding their progress to the west.