As the Algarve coast is mostly supplied by water from the Mediterranean, it's significantly warmer than the west coast of Portugal. Therefore, it stands to reason that the sea around the Algarve is warmer on the east side than the west. The Algarve is also prone to warm winds coming up from North Africa. Although the winds can last for up to several days, you do find that the sea becomes noticeably warmer. You will also feel an increase in water temperature from the start of the holiday season compared with near the end – August and September.