Learn Hardcore Indonesian: Jas hujan saya basah, jadi saya jemur di balkon. - My raincoat is wet, so I dry it on the balcony.

jaket hujan: a rain jacket style.
mantel hujan: raincoat (more formal/literary).
ponco: poncho. Note that jas by itself often means a suit jacket, but the compound jas hujan is standard for “raincoat.”

Why is the possessor saya placed after the noun (jas hujan saya) instead of before it?

In Indonesian, possessive pronouns follow the noun: jas hujan saya = my raincoat. You can also use clitics:

jas hujanku (my raincoat, informal)
jas hujanmu (your raincoat, informal)
jas hujannya (his/her/its raincoat; or “the raincoat” in context) You can also say jas hujan punya saya for emphasis. Don’t say saya jas hujan.

Do we need adalah in Jas hujan saya basah?

No. With adjectives as the predicate, you don’t use adalah. Say Jas hujan saya basah. Use adalah mainly before a noun phrase, e.g., Dia adalah dokter.

Where is the tense? How would I say was wet or is getting dried?

Indonesian doesn’t mark tense on the verb. Use time words or aspect markers:

Past: tadi or sudah (e.g., Tadi jas hujan saya basah; Jas hujan saya sudah basah).
Progressive: sedang or colloquial lagi (e.g., Saya sedang/lagi menjemur).
Future: akan (e.g., Jas hujan saya akan basah “will get wet”).

What does jadi do here? Could I use karena or makanya instead?

Here jadi is a conjunction meaning “so/therefore”: … basah, jadi …. You can also write it as a new sentence: … basah. Jadi, ….

karena means “because” and introduces the cause: Karena jas hujan saya basah, saya menjemurnya di balkon.
makanya is colloquial “that’s why”: Jas hujan saya basah, makanya saya jemur di balkon.
Note: jadi can also mean “to become” as a verb (not the case here).

Is saya jemur correct, or should it be saya menjemur?

Both can be heard. Saya jemur is casual/colloquial (dropping the meN- prefix). In neutral or formal style, use Saya menjemur (sesuatu). In careful writing you’d prefer menjemur.

Does jemur need an object? Where is “it” in the second clause?

Yes, (men)jemur normally takes an object (the thing being dried). In casual speech you can drop it if obvious from context. More explicit options:

Jadi saya menjemur jas hujan saya di balkon.
Jadi saya menjemurnya di balkon. (the -nya = “it”)

Can I make it passive with dijemur?

Yes: Jas hujan saya dijemur di balkon focuses on the raincoat (agent omitted). If you want to mention the agent, add oleh: … dijemur di balkon oleh saya (often omitted in practice). Another natural alternative is the ku- form: Kujemur jas hujan di balkon (informal, “I dry my raincoat…”).

Why is it di balkon with a space? When do I attach di-?

As a preposition meaning “in/at/on,” di is written separately: di balkon. When di- is the passive verb prefix, it attaches to the verb: dijemur. So: di balkon (place), but dijemur (passive verb).

Does di balkon mean on the balcony or at the balcony? What about di atas balkon?

di is a general locative (“in/at/on”), so di balkon naturally means “on/at the balcony.” di atas means “on top of/above” a surface; di atas balkon would be odd unless you literally mean on top of the balcony structure (e.g., on the roof/railing).

What’s the difference between balkon, teras, and beranda?

balkon: an elevated balcony (often on an upper floor) protruding from a building.
teras: a ground-level terrace/porch.
beranda: a veranda/porch, often covered; can be ground-level.
Spelling note: Indonesian standard is balkon (not balkoni).

What’s the nuance of basah? How do I say damp or very wet?

basah = wet.
lembap (also spelled colloquially lembab) = damp/moist/humid. To intensify:
Neutral: sangat basah, basah sekali.
Colloquial: basah banget. You can add aspect too: masih basah (still wet), sudah basah (already wet).

Could I use yang here, like Jas hujan saya yang basah…?

yang highlights/restricts the noun. Jas hujan saya yang basah means “the raincoat of mine that is wet (as opposed to another one).” Use it when you’re contrasting or specifying. In the original sentence, yang isn’t needed.

Are there register alternatives for saya? And what about ku-/ -ku?

Yes:

aku (informal), gue (Jakarta colloquial), Anda (formal/polite).
Possessives: jas hujanku (my raincoat, informal), jas hujan Anda (formal).
Subject clitics: Kujemur jas hujan di balkon = “I dry my raincoat…” (ku- = I, informal/literary). -ku attaches to nouns; ku- attaches to verbs.

Is there a noun related to jemur, like “drying rack”?

Yes: jemuran refers to the clothesline/drying rack or the stuff being dried. Example: Saya taruh di jemuran di balkon (“I put it on the drying rack on the balcony”).