Prije nego što isplovimo, provjerimo vremensku prognozu i morsku struju.

Prije nego što means before when it introduces a whole clause with a verb:

• Prije nego što isplovimo = Before we set sail

Use plain prije when it is followed by a noun or noun phrase, not a full clause:

• prije puta = before the trip
• prije polaska = before departure

So the basic difference is:

• prije + noun
• prije nego (što) + verb clause

Yes. Što is often optional here.

All of these are possible:

• prije nego što isplovimo
• prije nego isplovimo

The version with što is very common and sounds full/standard. Learners will hear both.

Because Croatian often uses the present tense form after words like before, when, if, as soon as, especially with a perfective verb, to refer to a future action.

Here, isplovimo comes from isploviti and means something like when we set sail / before we set sail.

So although the form looks present, the meaning is future relative to the main action.

This is very normal in Croatian:

• Kad dođem, nazvat ću te. = When I arrive, I’ll call you.
• Prije nego što isplovimo... = Before we set sail...

Isploviti means to set sail, to sail out, or to leave port by boat/ship.

It is more specific than a general verb like ići (to go). It implies movement by sea and usually the beginning of a voyage.

So in this sentence, it fits very naturally: before leaving by boat, we check the forecast and the current.

Formally, it matches the 1st person plural form, and in this sentence it is understood as an inclusive imperative/exhortation:

• provjerimo = let’s check

Croatian often uses this form for suggestions involving the speaker and others:

• Idemo! = Let’s go!
• Pogledajmo. = Let’s look.
• Provjerimo... = Let’s check...

So the sentence sounds like a practical instruction or suggestion: Before we set sail, let’s check...

Because they are direct objects of provjerimo / provjeriti (check), so they go in the accusative case.

Both nouns are feminine singular:

• vremenska prognoza → vremensku prognozu
• morska struja → morsku struju

The adjectives also change to match the nouns:

• vremenska → vremensku
• morska → morsku

So the whole object phrases are in the accusative.

Vremenska prognoza is the standard expression for weather forecast.

You may also encounter prognoza vremena, which is understandable and also possible, but vremenska prognoza is the more usual everyday phrase.

In this sentence, provjeriti vremensku prognozu is the most natural choice.

Because Croatian has no articles like English a/an/the.

So:

• vremensku prognozu can mean a weather forecast or the weather forecast
• morsku struju can mean a sea current or the sea current

The context tells you which meaning is intended. In this sentence, English would usually say the weather forecast and the sea current/current conditions, but Croatian does not need a separate word for the.

Because the verb ending already tells you the subject.

Both isplovimo and provjerimo have the -mo ending, which marks we.

So Croatian usually omits the pronoun unless it is needed for emphasis or contrast.

• isplovimo = we set sail
• provjerimo = let’s check / we check

You could add mi, but it would sound more emphatic:

• Prije nego što mi isplovimo...

That is not necessary in a neutral sentence.

Yes, in this sentence it is natural and correct.

The clause Prije nego što isplovimo comes first, and it is separated from the main clause by a comma:

• Prije nego što isplovimo, provjerimo...

If you reverse the order, you would usually write:

• Provjerimo vremensku prognozu i morsku struju prije nego što isplovimo.

So the comma is especially expected when the subordinate clause comes first.

Yes. Croatian word order is fairly flexible.

You can also say:

• Provjerimo vremensku prognozu i morsku struju prije nego što isplovimo.

Both versions are correct. The difference is mostly about emphasis:

• Prije nego što isplovimo, ... puts the time condition first
• Provjerimo ..., prije nego što isplovimo puts the action first

The original version sounds very natural because it sets the scene first: before we leave, let’s check...

Yes, struja can mean electric current / electricity, but it can also mean current in the sense of moving water or air.

So:

• električna struja = electric current
• morska struja = sea current
• zračna struja = air current

In this sentence, morska struja clearly means the movement of seawater, not electricity.