A strong wind of monsoon origin that blows from between the northwest and north-northwest and sets in about the end of May or early June in the historic Seistan district of eastern Iran and Afghanistan. It continues almost without cessation until about the end of September. From its duration it is known as the wind of 120 days (bad-i-sad-o-bistroz). It sometimes reaches a velocity of more than 31 m s⁻¹ (70 mph) and carries much sand and dust. This sand blast is very erosive; buildings are eaten away and undercut near the ground. In some places the sand is deposited as wandering dunes, which overwhelm buildings and choke water supplies. All buildings in the region have blank walls on the windward side. The seistan is associated (along with the European etesians, and the shamal) with the deep summertime low over northwest India.