haroukeihou de hunayoi ga sinpai desu.

波浪警報 is read はろうけいほう.

• 波浪 = waves, sea swells
• 警報 = warning, alarm

So 波浪警報 is a high wave warning or wave warning.

This is a fairly formal word, often used in weather reports or official announcements.

船酔い is read ふなよい.

Even though 船 can be read せん in compounds, here it uses the native Japanese reading ふな. That is common in some everyday words.

• 船 = boat, ship
• 酔い = drunkenness / feeling sick / nausea

So 船酔い means seasickness.

Here, で shows the cause or reason: because of, due to.

So:

• 波浪警報で = because of the wave warning / due to the high wave warning

This is different from other uses of で, such as:

• location of an action: 学校で勉強する
• means/tool: 箸で食べる

In this sentence, it is the reason use.

Because 波浪警報 is not the thing being described as worried. It is the reason for the worry.

• で marks the cause: because of the wave warning
• が would mark a subject, which would create a different structure

So the sentence is built like this:

• 波浪警報で = because of the wave warning
• 船酔いが心配です = seasickness is a worry / I’m worried about seasickness

In X が 心配です, the thing marked by が is the thing that is causing concern.

So:

• 船酔いが心配です = I’m worried about seasickness
• literally, something like Seasickness is a concern

This pattern is very common:

• 明日の天気が心配です = I’m worried about tomorrow’s weather
• 試験の結果が心配です = I’m worried about the test results

So が marks the thing you are worried about.

心配 is usually used as a noun or na-adjective, not as a plain independent verb in this kind of sentence.

So:

• 心配です = is worrying / is a concern
• 心配しています = am worrying / am concerned

In this sentence, 心配です sounds like a simple statement of concern. It is very natural.

You can think of 船酔いが心配です as:

• Seasickness is a concern
• more naturally in English: I’m worried about seasickness

Both can be natural, but the nuance is a little different.

• 心配です: states your concern in a simple, neutral way
• 心配しています: emphasizes that you are actively worrying, or that the concern is ongoing

So:

• 波浪警報で船酔いが心配です。 = I’m worried about seasickness because of the wave warning.
• 波浪警報で船酔いを心配しています。 = I’m worrying about seasickness because of the wave warning.

The first one is more straightforward and common in everyday speech.

Because 心配です does not take a direct object with を.

With the pattern X が 心配です, the thing you are worried about is marked by が.

However, if you use the verb phrase 心配する, then を can appear:

• 船酔いを心配する = to worry about seasickness

So:

• 船酔いが心配です = correct
• 船酔いを心配です = incorrect
• 船酔いを心配しています = correct

Japanese often leaves out the subject when it is understood from context.

So 波浪警報で船酔いが心配です naturally means something like:

• I’m worried about seasickness because of the wave warning
• or possibly We’re worried about seasickness...

The exact subject depends on context. In many situations, listeners will assume I unless there is some reason to think otherwise.

It can suggest either one depending on context, but most often it means:

• I’m worried about getting seasick

That is because 船酔い refers to the condition of seasickness, and in a sentence like this it often refers to the speaker’s concern about that happening.

Still, Japanese is a little broader here than English. The sentence can also sound like:

• Seasickness is a concern because of the high wave warning

So context tells you whether it is personal or more general.

Yes, it is natural, especially in a concise spoken or written context.

It has a slightly compact feel, almost like something you might say briefly when explaining your concern:

• 波浪警報で、船酔いが心配です。

In fuller conversation, someone might also say:

• 波浪警報が出ているので、船酔いが心配です。
• 波が高そうなので、船酔いが心配です。

These are a bit more explicit, but your original sentence is still natural.

Because Japanese can express reason in several ways, and で is one of them.

Common ways to say because include:

• ので
• から
• で for certain kinds of causes, especially situations, conditions, or reasons

Here, 波浪警報で is a compact way to say because of the wave warning.

Compared with ので or から, で can sound shorter and more matter-of-fact.

Yes, but it would change the nuance.

For example:

• 船酔いは心配です。

This sounds like As for seasickness, I’m worried. It adds topical contrast or emphasis.

But in the original sentence:

• 船酔いが心配です

が is the most natural choice because it marks the specific thing that is the concern.

You could also say:

• 波浪警報で、船酔いは心配です。

This might sound like you are contrasting seasickness with other possible concerns. Without that contrast, が is usually better.

It behaves like both, depending on the structure.

心配 is basically a na-adjective and also a noun.

Examples:

• 心配です = is worrying / I’m worried
• 心配なこと = a worrying thing
• 心配があります = there are worries / I have concerns

In your sentence, 心配です is the standard predicate form.

So even though English uses worried like an adjective, Japanese expresses it with 心配です very naturally.