This picture taken in August 1992 shows the wind patterns in the
Indian Ocean that permitted ocean travel at regular intervals. North
of the equator north-east winds prevail in the winter and south of
the equator north-west winds predominate. During the rest of the year
winds blow steadily from the south and west.
For pictures at another site showing how spices and silks traveled to Europe through the Indian Ocean prior to the Portuguese arrival see animated Trade Maps