There are only two repeat two weather stations in the Algarve.....Faro Airport and Sagres!
For example "Auntie" has a weather report for Lagos but is actually based on readings for Sagres. Sagres and environs, sticking out into the Atlantic has a micro-climate all of its own.....and often bears no relationship to prevailing conditions in Lagos 35 kms away.
Even the Portuguese Met service at www.meteo.pt bases its forecasting on these stations. Given the size of the Algarve there is therefore every chance that forecasts will not be accurate.