  In this paper we investigate the correlation between the atmospheric
perturbations at Paranal Observatory and the Chilean coast tides, which are
mostly modulated by the 14-day syzygy solar-lunar tidal cycle. To this aim, we
downloaded 15 years (2003-2017) of cloud coverage data from the AQUA satellite,
in a matrix that includes also Armazones, the site of the European Extremely
Large Telescope. By applying the Fast Fourier Transform to these data we
detected a periodicity peak of about 14 days. We studied the tide cycle at
Chanaral De Las Animas, on the ocean coast, for the year 2017, and we
correlated it with the atmospheric perturbations at Paranal and the lunar
phases. We found a significant correlation (96%) between the phenomena of short
duration and intensity (1-3 days) and the tidal cycle at Chanaral. We then show
that an atmospheric perturbation occurs at Paranal in concomitance with the low
tide, which anticipates the full (or the new) moon by 3-4 days. This result
allows to improve current weather forecasting models for astronomical
observatories by introducing a lunar variable.
