From AMS Glossary
In northern Sumatra, a warm, dry local wind blowing on the plains of Deli, Langkat, and Lerdang.
It is caused by the east monsoon blowing across the Barisan Mountains and descending on the leeward side as a foehn. The bohorok occurs in May and is prevalent through September; it is feared because of its effect on the tobacco plantations on the plains of Deli. On the windward side of the mountains, "bohorok days" have more rain than usual.