For daily (and longer) forecasts, try:
Institute of Meteorology, Portugal – English language version giving three, five and 10-day forecasts.
BBC Weather – link to the five-day forecast for Lisbon (go to Find A Forecast for other Portuguese towns.
Climate Charts.com has weather statistics for a number of key locations around Portugal. To see them, click here.
ClimateTemp.info has more detailed statistics – everything from windspeed to number of frosty days. The site is a bit messy but scroll down to find links to stats for towns around the country. Click here.
Portugal’s Meteorological Institute also has an excellent site. Most of the statistical information is only in Portuguese but the charts are reasonably easy to understand:
For annual monthly averages – click here and select max, min or average temperature or rainfall (‘precipitacao’) on the right.
For monthly statistics from the past 30 years, click here and select from the list of locations on the right.