Some values are measured (buoys, rain gauges, satellites); many are computed by models (forecasts, CAMS air quality, ERA5). Models cover everywhere but can be wrong locally.
Data and trust
Three kinds of data in this app:
Observations: measured by an instrument (TAO buoys, island rain gauges, satellite SST). Real, but only where and when the instrument is.
Reanalysis (ERA5): past weather rebuilt by combining millions of observations with a weather model. Complete and consistent, but smoothed over about 25 km cells, so it can under-estimate local downpours on a small island.
Forecasts and model analyses (Open-Meteo weather and marine, CAMS air quality, ECMWF seasonal): computed. Excellent for trends and warnings, less exact for one spot and one hour.
Samui is small compared with most model grid cells, so treat model values as "the area around Samui".