The Evolution of Precipitable Water and Precipitation over the Island of Tahiti from Hourly to Seasonal Periods

The Island of Tahiti (French Polynesia) has a complex meteorological context governed by the South Pacific convergence zone on a large scale and the topography of a high volcanic island on the orographic scale. The island is subject to heavy rainfall (up to 8000mm year(-1) in some areas), mainly during the rainy season (November to April), generating significant geo-morphological changes and property damage each year. To better understand the underlying complex mechanisms leading to precipitation over a broad range of timescales (from hourly to seasonal), we have analysed eight years of data (2001-2008) coming from five sources: a radiometer, radiosoundings, a GPS, Era-Interim reanalysis, and two rain gauges, all located close to or inside the Matatia valley, a small typical Tahitian valley. In particular, we have decomposed the precipitable water distribution into two statistical distributions corresponding to the dry and wet seasons. The time evolution of precipitable water in the dry season is characterized by a log-normal distribution, while the precipitable water time evolution in the wet season is characterized by a reverse log-normal distribution. The bimodality of the probability distributions describing the dynamical processes involved in the Tahiti climate is confirmed by the study of the diurnal evolution in absolute humidity, precipitable water, and precipitation.