यात्रा पर मौसम का असर है।

In this sentence, पर means on/upon in the sense of affecting something.

So यात्रा पर literally means on the journey/trip.
That gives the structure:

• यात्रा पर = on the trip / on travel
• मौसम का असर = the effect of the weather
• है = is

So the whole sentence is literally something like:

The weather’s effect is on the trip.

Natural English: The weather affects the trip or The weather has an effect on the trip.

This is a very common pattern in Hindi:

• X पर Y का असर है = Y has an effect on X

For example:

• सेहत पर खाने का असर है। = Food has an effect on health.

असर means effect, impact, or influence.

It is generally treated as a masculine noun in Hindi. That is why you see:

• मौसम का असर

and not की असर.

Because असर is masculine singular, the possessive marker is का.

Because का / की / के agrees with the noun that follows it, not with the noun before it.

Here:

• मौसम = weather
• असर = effect

The phrase means the weather’s effect / the effect of the weather.

Since असर is masculine singular, Hindi uses का:

• मौसम का असर

Compare:

• मौसम का असर = the effect of the weather
• मौसम की वजह = the reason because of the weather

In the second example, वजह is feminine, so की is used.

Hindi often expresses ideas with noun phrases plus होना rather than using a direct action verb the way English does.

So instead of saying something exactly like The weather affects the trip, Hindi can say:

• यात्रा पर मौसम का असर है।
• literally: There is the weather’s effect on the trip.

This is a very natural Hindi way to express the idea.

A closely related version is:

• यात्रा पर मौसम का असर पड़ता है।

That also means The weather affects the trip or The trip is affected by the weather.

The version with है states the existence of an effect.
The version with पड़ता है often feels a bit more verbal/dynamic: an effect falls/is exerted.

है is the present tense of होना (to be).

Here it links the idea together and means is:

• यात्रा पर मौसम का असर है।
• There is an effect of the weather on the trip.

Without है, the sentence would sound incomplete in standard Hindi.

Yes. That is also grammatical.

Hindi word order is flexible, especially with postpositional phrases and topic/focus.

These are both possible:

• यात्रा पर मौसम का असर है।
• मौसम का असर यात्रा पर है।

The difference is mostly one of emphasis:

• यात्रा पर मौसम का असर है may put early attention on the trip
• मौसम का असर यात्रा पर है may put early attention on the weather’s effect

Both mean essentially the same thing.

Because ने is used mainly with many perfective transitive verbs, and this sentence is not built that way.

This sentence is not Weather did something with a normal action verb.
Instead, it is a possession/existence-type structure:

• मौसम का असर है = there is an effect of the weather

So ने is not needed.

Yes, यात्रा is a feminine noun.

But in this sentence, that does not affect का in मौसम का असर, because का agrees with असर, not यात्रा.

It also does not change पर, because postpositions like पर do not change for gender.

So:

• यात्रा = feminine
• यात्रा पर = on the trip
• no visible gender change there

Both can often mean journey/trip, but they have slightly different flavor:

• यात्रा can sound a bit more formal, literary, or broad.
• सफ़र is very common in everyday speech and often feels more conversational.

So you could also hear:

• सफ़र पर मौसम का असर है।

That would still be understandable, though यात्रा पर मौसम का असर है sounds a bit more formal/written.

Yes, as a learning aid, that literal translation is useful.

Literal structure:

• यात्रा पर = on the trip
• मौसम का असर = the weather’s effect
• है = is

So: The weather’s effect is on the trip.

But in natural English, you would usually say:

• The weather affects the trip
• The weather has an effect on the trip
• The trip is affected by the weather

Yes, very similar.

• यात्रा पर मौसम का असर है। = The weather has an effect on the trip.
• यात्रा मौसम से प्रभावित है। = The trip is affected by the weather.

The second version uses:

• से = by/from
• प्रभावित = affected/influenced

That version is a bit more formal and closer to a passive-style expression.

It is natural and correct, but depending on context, native speakers might also say things like:

• मौसम की वजह से यात्रा प्रभावित है।
• मौसम का यात्रा पर असर पड़ रहा है।
• मौसम से यात्रा पर असर पड़ता है।

Your original sentence is good Hindi, especially in a neutral or slightly formal style.

Hindi does not have articles like English a/an/the.

So nouns often appear without any equivalent word:

• यात्रा = trip / the trip / a trip
• मौसम = weather / the weather
• असर = effect / an effect / the effect

The exact meaning depends on context.

That is why यात्रा पर मौसम का असर है can be understood naturally without extra words for the or a.