The Azores are considered a sub-tropical climate zone. What does this mean? Normally sub-tropical weather refers to humid and hot summers that last quite long and dry mild winters. In the Azores the climate might vary a bit per island and even one single island can have distinctively different climate zones depending on mountains, wind, valleys, rivers, lakes etc.
In the case of the Central Group of the Azores this does not mean you can go and about in a T-shirt and shorts all year. Winters can be surprisingly good with temperatures of 20-22 Degrees Celsius (68 to 71,5 Fahrenheit) during the day but in the night expect temperatures of around 14 Degrees Celsius or less (57 and below Fahrenheit). A heater in the house is not and indulgence in luxury and depending on the size of the house you might consider reverse airconditioning, heat pump system, Central heating (either floor or radiators) on gas or wood pellets or just an old fashioned wood stove in a central location.
If you have a stone house you might be confronted with condensation on the inner walls especially on the wind side of the house. You can deal with this by insulating your outside wall and use of dehumidifiers or air conditioning units. When rebuilding an old house be aware that most of your costs will be going in waterproofing the foundation, walls, roof insulation and proper glazing. When insulating your house be aware to incorporate a ventilation system.
Basements can get a lot more dry with installing proper ceiling fans. The modern ones still offer a classic look but use a fraction of the energy and you can leave them on at low speed 24/7. They prevent condensation forming in these lesser ventilated and cooler areas of the house.
Spring will often bring snow on Pico Mountain (at 2350 meters a respectable height) and this snowy mountain, with the proper wind direction will bring very chilled air down the mountain. Early and even late spring still bring snow to Pico and plenty of rain to the islands.
If you have an old stone house installing proper roof gutters is a good way to keep the lower walls of your house dry. Do not forget volcanic rock has been used and it acts pretty much like a sponge…
We have occasional storms but unlike what you see in countries with wooden houses the stone cottages and concrete houses on the islands are pretty well engineered to withstand heavy winds. Hurricanes bring the risk of flying debris and good outside shutters are a safety feature one might consider especially if you have a house with large glass doors and windows. Do not worry, strong hurricanes are a much rarer event in the middle of the Atlantic compared to the Gulf of Mexico and the Caribbean. Direct hits are even more rare. It makes good sense to use tiles with screw holes for the last one or two rows on your roof, cement in the side rows and the tiles on the top and you should be able to weather almost any storm in the Atlantic.
One might think after reading all of this that sub-tropical might be a bit of a too flattering term to describe the island climate but in general we are experiencing very mild weather and not too often real hot weather. Summer weather can extend easily until the end of October. For people who want to be active the climate is near perfect and summers are pretty warm for those who prefer to spend their days on the beach as well.