While God can alter regional or even global climates if he wishes, typically, he acts more conservatively, using existing conditions in the world to accomplish his purposes. In this case, simply directing the party to leave around August would have placed them not only in a time of harvest, but also at the beginning of the monsoon season. Perhaps there was a divine reason for the eight years in the wilderness of which the family was unaware. Perhaps the Lord was waiting for the climatic conditions that would enable the journey.