Answer:Once a month at perigee (the point in the orbit of the moon or a satellite at which it is nearest to the earth.)
Explanation:when the moon is closest to the Earth, tide-generating forces are higher than usual, producing above average ranges in the tides. About two weeks later, at apogee, when the moon is farthest from the Earth, the lunar tide-raising force is smaller, and the tidal ranges are less than average.