Ben de yarınki geziye hevesliyim, ama hava durumuna bakacağım.

Here, de means too / also.

So Ben de... means I too... or Me too...

It is written separately because this is the particle de, not the location suffix -de/-da meaning in / at / on.

Compare:

• Ben de geliyorum. = I’m coming too.
• Evdeyim. = I’m at home.

In your sentence, de follows ben, so the emphasis is specifically on I too.

That’s true: Turkish often leaves out subject pronouns because the verb ending already shows the person.

For example, hevesliyim already means I am enthusiastic/eager.

So in theory, ben is not strictly necessary. But it is included here for emphasis or contrast:

• Ben de yarınki geziye hevesliyim. = I’m excited about tomorrow’s trip too.

Using ben makes the I too idea clearer and stronger.

yarınki comes from:

• yarın = tomorrow
• -ki = a suffix that turns it into something like the one for tomorrow or tomorrow’s

So:

• yarınki gezi = tomorrow’s trip / the trip tomorrow

This -ki suffix is very common with time and place expressions:

• dünkü toplantı = yesterday’s meeting
• bugünkü ders = today’s lesson
• evdeki kitap = the book in the house

geziye is the noun gezi plus the dative ending -(y)e:

• gezi = trip / excursion
• geziye = to the trip or, more naturally here, about the trip

The reason is that hevesli olmak often uses the dative for the thing someone is eager or enthusiastic about.

So:

• geziye hevesliyim = I’m eager for / enthusiastic about the trip

This is one of those cases where Turkish uses a case ending where English uses a preposition like about or for.

It breaks down like this:

• hevesli = eager, keen, enthusiastic
• -yim = I am

So:

• hevesliyim = I am eager / enthusiastic

The y appears because the adjective ends in a vowel, and Turkish often inserts y before a vowel-starting ending.

Similar examples:

• mutluyum = I am happy
• hazırım = I am ready
• heyecanlıyım = I am excited

Not exactly.

• hevesli usually means eager, keen, enthusiastic
• heyecanlı usually means excited, and sometimes it can also suggest nervous excitement

So in this sentence, hevesliyim sounds like the speaker is positively looking forward to the trip, rather than just feeling emotional excitement.

In many situations, both could work, but they are not perfect substitutes.

hava durumu is a very common expression meaning the weather or the weather forecast, depending on context.

Literally, it is built from:

• hava = air / weather
• durum = state / condition
• durumu = part of the noun-compound structure

In everyday use:

• hava durumuna bakmak usually means to check the weather or to check the forecast

So even if the literal parts look a little different from English, it is best learned as a set phrase.

This is because hava durumu is a noun compound.

The second word carries a compound ending:

• hava durumu

Then, when you add a case ending, it goes onto the whole compound:

• hava durumu
  • -na → hava durumuna

So the structure is:

• hava durum-u-na

This pattern is very common in Turkish:

• okul kapısı → okul kapısına
• otobüs durağı → otobüs durağına

Also, the verb bakmak requires the dative, which is another reason you need -na here.

In Turkish, bakmak usually takes the dative case when it means look at or check.

So:

• sana bakıyorum = I’m looking at you
• telefona baktım = I looked at the phone
• hava durumuna bakacağım = I’ll check the weather

This is just a verb pattern you need to learn:
bir şeye bakmak = to look at / check something

It does not use the direct-object form the way English often does.

It comes from the verb bakmak = to look / to check.

Breakdown:

• bak- = verb stem
• -acak = future tense marker
• -ım / -im / -um / -üm = first person singular ending

So:

• bakacağım = I will look / I am going to check

In natural English, here it would often be translated as I’m going to check.

No, Turkish word order is flexible, but changing it changes the emphasis.

The original:

• Ben de yarınki geziye hevesliyim, ama hava durumuna bakacağım.

This sounds natural and balanced:

1. first, the speaker says they are enthusiastic about the trip
2. then, ama introduces a contrasting idea: they still want to check the weather

You could move things around, but the emphasis would shift. For example:

• Yarınki geziye ben de hevesliyim... puts a bit more focus on tomorrow’s trip
• Ben yarınki geziye de hevesliyim... could suggest I’m also enthusiastic about tomorrow’s trip, perhaps in addition to something else

So the original sentence is a very natural choice.