Other natural hazards are heat waves where temperatures can reach over with a heat index of which is caused by the low humidity on clear days. Cold waves are also curious in Iquitos: cold air from the tip of the continent driven by the dynamics of the atmosphere, comes to town and causes a drop in temperature, moderate rainfall and thunderstorms. The trade winds also come to cause gales reaching . In October 2012, Iquitos experienced high temperatures and heavy thunderstorms.