Learn Hardcore Turkish: Üstelik rüzgar doğudan esiyordu, kapı sürekli açılıyordu. - Moreover, the wind was blowing from the east and the door kept opening.

Üstelik means “what’s more / on top of that.” It introduces an additional point, often one that makes the situation worse, more surprising, or more convincing. It’s most natural at the start of a clause: Üstelik rüzgar doğudan esiyordu... You could move it, but initial position is the default. Alternatives:

Ayrıca = additionally (neutral)
Hem de = and what’s more (colloquial, emphatic)
Hatta = even (for a stronger, sometimes surprising add-on)
Dahası = furthermore (formal)

A comma after Üstelik is optional; most writers don’t put one unless there’s a pause for emphasis.

Why is there just a comma between the two clauses? Shouldn’t there be ve or bu yüzden?

In Turkish, it’s common to place two related clauses side by side with a comma. It can imply sequence or a cause–effect relationship that the reader infers from context. If you want to make the link explicit:

Coordination: Üstelik rüzgar doğudan esiyordu ve kapı sürekli açılıyordu.
Cause: Üstelik rüzgar doğudan esiyordu, bu yüzden kapı sürekli açılıyordu.

Could I say Doğudan rüzgar esiyordu instead? What changes with word order?

Yes. Word order in Turkish is flexible. Default is Subject–Object–Verb, but fronting an element emphasizes it.

Rüzgar doğudan esiyordu (neutral: about the wind; source is backgrounded)
Doğudan rüzgar esiyordu (puts extra emphasis on “from the east”)

Both are correct; choose based on what you want to highlight.

What does -dan in doğudan mean? Why not -den?

-dan/-den is the ablative case meaning “from.” Vowel harmony picks the form:

After back vowels (a, ı, o, u): -dan → doğudan, batıdan
After front vowels (e, i, ö, ü): -den → kuzeyden, güneyden

No apostrophe is used because doğu here is a common noun, not a proper name.

How do you pronounce the ğ in doğudan?

Turkish ğ (yumuşak g) isn’t a full consonant; it lengthens or glides the preceding vowel. Doğudan is roughly “doo-uu-dan,” with a lengthened “o/u” transition: [doːudan]. Don’t pronounce a hard “g.”

Is rüzgar spelled correctly, or should it be rüzgâr?

Both are seen. Rüzgar (without the circumflex) is the everyday spelling; rüzgâr marks a slightly lengthened/“palatal” a and is preferred by some style guides. The consonant is plain g (not ğ). Either spelling will be understood.

What exactly is the tense in esiyordu and açılıyordu?

It’s the past continuous: stem + progressive + past.

es-iyor-du → “was blowing”
aç-ıl-ıyor-du → “was opening” (intransitive/passive) Notes:
The buffer -y- appears before -or/-yor when needed.
The past ending -dı/-di/-du/-dü follows vowel harmony: esiyor-du (last vowel “o” → du).

Why açılıyordu and not açıyordu?

açmak = to open (transitive): someone/something opens something.
açılmak = to open / to be opened / to open by itself (intransitive/passive). A door opening due to the wind uses the intransitive/passive: Kapı açılıyordu. Compare:
Kapıyı açıyordu. (He/She was opening the door.)
Kapı açılıyordu. (The door was opening / being opened.)

Does kapı mean “the door” even without an article?

Yes. Turkish has no articles. Bare nouns can be definite from context. Kapı here naturally reads as “the door” (the relevant door in the situation). If you needed “a door” (non-specific), you could say bir kapı. For a definite direct object you’d mark it with the accusative, but here kapı is the subject.

What nuance does sürekli add? Could I use hep or durmadan instead?

sürekli = continuously/constantly (suggests ongoing or very frequent repetition)
hep = always/all the time (broader, slightly less “technical”)
durmadan = without stopping (colloquial, “nonstop” feel)
devamlı = continually (near-synonym of sürekli) All work, with small nuance differences: Kapı sürekli/hep/durmadan açılıyordu.

Could I use a more “habitual past” form like açılırdı?

Yes, and it slightly changes aspect:

açılıyordu = was (kept) opening at that time (ongoing background)
açılırdı = would/used to open (habitual tendency in the past) Choose based on whether you want ongoing background action or a general habit.

Is there a more formal way to say the progressive, like -mekte?

Yes. The progressive can be expressed with -mekte (present) and -mekteydi (past progressive, formal/literary):

Rüzgar doğudan esmekteydi, kapı sürekli açılmaktaydı. This is stylistically elevated; everyday speech uses -yor/-yordu.

Can I make the cause explicit with a postposition like yüzünden?

Absolutely:

Rüzgarın doğudan esmesi yüzünden kapı sürekli açılıyordu.
Doğudan esen rüzgar yüzünden kapı sürekli açılıyordu. These mean the door kept opening “because of” the east wind.

Where should I place sürekli in the clause?

Default is before the verb complex: Kapı sürekli açılıyordu. You can front it for emphasis (Sürekli kapı açılıyordu) or, less commonly, place it sentence-final for a spoken, afterthought feel (Kapı açılıyordu sürekli). The pre-verbal position is the most neutral.