Earliest meteorological readings in San Fernando (Cadiz, Spain, 1799-1813)

Cadiz and San Fernando are two towns close to each other with a wealth of meteorological records due to their connection with the Spanish Royal Navy officers and enlightened merchants. Several previous works have already recovered a significant number of meteorological records of interest in these localities. However, more than 40 000 daily meteorological observations recorded at the Royal Observatory of the Spanish Navy (located in San Fernando) during the period 1799-1813 were previously unnoticed; they remained neither digitized nor studied. Here, we have carried out this important task, describing the different steps undertaken to achieve it as well as the results obtained. The dataset is composed of different meteorological variables such as atmospheric pressure, air temperature, precipitation, and state of the sky. As a first step a quality control was carried out to find possible errors in the original data or in the digitization process. Moreover, the antique units were converted to modern units. Also, the metadata and an analysis of the data are described. The dataset is freely available to the scientific community and can be downloaded at https://doi.org/10.5281/zenodo.7104289.