Vinden er kraftig.

Because vinden is the definite form of the noun.

• vind = wind
• vinden = the wind

In Norwegian, the idea of the is usually attached to the end of the noun as a suffix.

Norwegian usually does not use a separate word like English the in simple cases like this. Instead, the definite article is added to the noun itself.

So:

• en vind = a wind
• vinden = the wind

That -en ending is doing the job that the does in English.

Er means is. It is the present tense of the verb å være, which means to be.

So the structure is:

• Vinden = the wind
• er = is
• kraftig = strong / powerful

This is a very common sentence pattern in Norwegian.

Because kraftig is an adjective describing the subject, and after er Norwegian uses adjectives in the same general way English does.

So:

• Vinden er kraftig = The wind is strong

Here, kraftig is a predicative adjective. It comes after the verb er, not directly before the noun.

Compare:

• en kraftig vind = a strong wind
  (adjective before the noun)

• vinden er kraftig = the wind is strong
  (adjective after er)

In this sentence, kraftig is the correct form.

A useful thing to know is that Norwegian adjectives can change form depending on gender, number, and how they are used. However, kraftig is one of those adjectives whose singular form often stays kraftig.

For example:

• en kraftig vind = a strong wind
• et kraftig slag = a powerful blow
• kraftige vinder = strong winds

So here, with vinden, kraftig is exactly the form you expect.

Vind is a noun. In Bokmål, it is normally:

• en vind
• vinden

So for a learner, the safest pattern is to remember it as a noun that takes en in the indefinite form and -en in the definite form.

Often yes, but not always perfectly.

Kraftig has a sense of strong, powerful, or forceful. With weather, it can suggest that the wind is quite forceful or intense.

Depending on context, English might translate it as:

• strong
• powerful
• heavy
• intense

So in weather language, kraftig vind is a very natural phrase for strong wind.

Yes, you could. Sterk also means strong.

But there is a slight nuance:

• sterk = strong in a general sense
• kraftig = forceful, powerful, intense

For wind and weather, kraftig often sounds especially natural. So Vinden er kraftig is a very idiomatic sentence.

Yes, in this simple sentence it is very similar:

• Vinden = subject
• er = verb
• kraftig = adjective

So the pattern is:

subject + verb + adjective

However, Norwegian main clauses follow the verb-second rule, so if something else comes first, the verb still stays in second position:

• I dag er vinden kraftig = Today, the wind is strong

That is a useful rule to remember as you learn more Norwegian.

A rough English-friendly guide is:

VINN-den er KRAF-ti

A few notes:

• vinden: the first syllable is stressed
• er is often pronounced quite lightly in normal speech
• kraftig often sounds like KRAF-ti, with the final g very weak or not clearly pronounced in many accents

So in connected speech, it may sound smoother and shorter than the spelling suggests.

Yes, very easily:

• Vinden = the wind
• er = is
• kraftig = strong / powerful

So this is one of those sentences where the Norwegian structure matches English very closely. That makes it a good beginner sentence for noticing how Norwegian handles the definite noun form.