In the south of the country is the Rub' al Khali, or Empty Quarter, the largest contiguous sand desert in the world. It slopes from about near the Yemeni border, northwestwards nearly to the Persian Gulf. Another sandy desert, the Nefud, lies in the north central part of Saudi Arabia, and it is connected to the Rub' al Khali by a broad swathe of sand dunes and gravel plains known as Dahna. Most of the country has very little precipitation, less than in many regions, and in the Rub' al Khali there may be no rain for a decade. The mountainous region of Asir in the southwest is wetter; it receives monsoon rains between May and October which may amount to .