Nocturnal Rainfall East of the Antilles Islands

Abstract

ABSTRACT We analyze nocturnal rainfall caused by the interaction of trade winds and land breezes on the windward flank of the islands of Guadeloupe, Dominica, and Martinique of the eastern Caribbean Antilles. Climatology for the 2000–2019 period and a nocturnal rainfall case study 8–9 February 2018 are supplemented by modern 5–25 km hourly resolution satellite and reanalysis products and station measurements that describe the diurnal cycle around the islands. Mean trade winds of 7 m s−1 decelerate upstream, ∂U/∂x less than −10−5 s−1, causing an increase in warm-cloud rainfall from 2 to 4 mm d−1 between 03:30 and 06:30 local time (local time is UTC-4). The incoming airflow has a characteristic Froude number less than 1 and stagnates on the windward slopes of these volcanic islands. Nocturnal land breezes spread toward the east coast about one-third of the time. Additional work considers whether air–sea interactions play a role. Low salinity and wave-induced turbulence to the east of the Antilles add buoyancy and moisture to the atmospheric boundary layer. Yet areas of low turbidity encircling the east Antilles suggest that nocturnal airflow creates a divergent “cushion” around Guadeloupe, Dominica, and Martinique. Thermal and orographic influences merge and rain falls over the eastern flank of the islands, contributing to the water resources.