Answer:
The Moon is at the closest part of its orbit around Earth; the Sun and the Moon form a straight line with Earth.
Step-by-step explanation:
The conclusion the captain could draw accurately is that;
The moon is probably at the closest part of its orbit moving round the earth. In addition, that the sun and the moon have formed a straight line with earth. This is due to the fact that high tides are higher and low tides are lower at a particular time each year.