This will be the coldest winter you will have survived.

Typically when you arrive in August/September, it will be +30°C, and may rarely go up to +40°C. Once you take about a week to get used to it, it becomes very comfortable weather. It's very dry, so the heat is very easy to deal with. You generally won't need a jacket at any hour of the day until mid-to-end of October/early November.

Weather through about mid-to-late November will be excellent. I remember 2 years ago, I was on the beach on November 15 (although this is not very typical). Typically for visitors beach season will end about mid-October. Weather will turn sour in mid-to-late November, and usually very quickly (within about a week), and usually it won't go back to being warm.

It will start raining more often in December, and you'll have one week of foliage (falling leaves) also around that time.

By mid-December you will want to be back in Romania in your warm, centrally-heated apartment. Even though the daytime highs will not drop too much below 15°C, the problem is that most houses are extremely poorly-insulated. Temps inside and outside are very similar in the winter, so while it may only be +10°C outside, it will be +13°C inside - miserable!!!!

It will be even more miserable because the air is very humid in the winter. When temps drop to 5°C in late Dec/early Jan, it will be bone-chilling cold.

This will last through about mid-March or so (although you may get lucky in late February, depending on the year).

I would rather spend a winter in Boston, than in Lisbon, because here even though it's --15°C (or even -30°C) outside, it's super dry, and it's warm once you get inside.

When looking for a room/apartment - a few things to look for:
-Double glazed windows
-Not-too-high ceilings (it's great in the summer, but sucks in the winter). You won't be able to heat the space.
-Make sure the windows close and there are no gaps.
-Heating/Aircon (either is very rare, especially in rented places)

The last place I rented was built in the 18th century after the quake of 1755 (refurbished recently), had meter-thick walls, new windows and was easy to heat. The two places below (one from the mid-70s, one from the late-80s) were both very difficult to keep warm.