Wet Season - Character of The Rainfall

Character of The Rainfall

In areas where the heavy rainfall is associated with a wind shift, the wet season becomes known as the monsoon. Since rainfall during the wet season is predominantly due to daytime heating which leads to diurnal thunderstorm activity within a pre-existing moist airmass, rainfall is mainly focused during the late afternoon and early evening hours within savannah and monsoon regimes. This also leads to much of the total rainfall each day falling during the initial minutes of the downpour, before the storms mature into their stratiform stage. While most locations have only one wet season, areas of the tropics can experience two wet seasons as the monsoon trough, or Intertropical Convergence Zone, can pass over locations in the tropics twice per year. Since rain forests have equitable rainfall throughout the year, they do not technically have a wet season.

The situation is different for locations within the Mediterranean climate regime. In the western United States, during the cold season from September through May, extratropical cyclones from the Pacific ocean move inland into the region due to a southward migration of the jet stream during the cold season. This shift in the jet stream brings much of the annual precipitation to the region, and also brings the potential for heavy rain and strong low pressure systems. The peninsula of Italy experiences very similar weather to the western United States in this regard.