A monsoon is a seasonal wind change bringing widespread long lasting rainfall across the world's tropical areas, including northern Australia during the wet season. In the buildup to the wet season, summertime heating warms up the land faster than the surrounding oceans, creating an area of low pressure. This helps to draw the monsoon trough south over the Australian continent with dry southeasterly trade winds shifting to moist north-westerly winds. When this wind change arrives, the tropics are affected by monsoonal conditions. During an active monsoon, the sky is filled with dark clouds bringing widespread rain and thunderstorms. These wet conditions can last for a few days or even a week or more. An active monsoon period can be followed by an inactive or break monsoon period. This is when the weather returns to pre-monsoonal or buildup conditions. Northern Australia typically sees about three monsoon bursts each wet season. Monsoonal rains deliver the majority of the annual rainfall across the tropical north. Although it can cause flooding and cut off roads, it's also vital for life across the tropical north.