Question

When is the tide the highest

Answer 1

-- the Earth is at perihelion (around January 5)
and
-- the Moon is at perigee (once every 27.32 days)

and

either
-- the Moon is New (once every 29.53 days)
or
-- the Moon is Full (once every 29.53 days)

Answer 2

when the moon is between the sun and the earth.