Electricity demand forecasting is becoming an essential tool for energy management, maintenance scheduling and investment planning. In small and isolated electric systems like in many islands, the power system is usually not extensively interconnected with enough number of electric generators and loads, hence it provokes an electric load shedding or forces the electric utility to take control actions such as temporary power outage. Despite this trouble, isolated territories are fortunate to have the possibility of estimating the population pressure in a very accurate manner, even at a daily level. This is possible thanks to the fact that entries to these territories are limited to ports and airports which in turn facilitate keeping the record of in/out flows to/from the territory. Investigating this problem, using the most classical and standard prediction techniques applied to the case of Balearic Islands (Spain) authors demonstrate how daily arrivals and people stocks improve accuracy of forecast.