Ég giska á að veðrið verði betra á morgun.

They are doing two completely different jobs:

• giska á is a fixed verb phrase meaning to guess / to reckon / to suppose
• á morgun is a time expression meaning tomorrow

So in:

• Ég giska á = I guess / I’m guessing
• á morgun = tomorrow

Even though both use á, they are not related grammatically in the sentence.

Here að introduces a subordinate clause, much like that in English:

• Ég giska á að ...
• I guess that ...

In natural English, that is often omitted, but in Icelandic að is normally kept in this kind of sentence.

So the structure is:

• Ég giska á = main clause
• að veðrið verði betra á morgun = subordinate clause

Verði is the subjunctive form of verða (to become / to be in this kind of context).

This is one of the most important grammar points in the sentence.

Why subjunctive?

Because the speaker is expressing a guess, not a certainty. The weather being better tomorrow is something uncertain, imagined, or assumed. Icelandic often uses the subjunctive in subordinate clauses when the content is not presented as a fact.

So:

• verður = indicative, more straightforward/factual
• verði = subjunctive, more uncertain/speculative

In this sentence, verði fits the idea of I guess that the weather will be better tomorrow.

The dictionary form is verða.

In this sentence, verði is the present subjunctive form.

A learner might recognize verða from sentences meaning:

• to become
• to happen
• or in weather/future-style expressions, something closer to be / turn out

Here veðrið verði betra is basically the weather will be / become better.

Veðrið means the weather.

The ending -ið is the definite article attached to the noun. Icelandic usually puts the at the end of the noun instead of using a separate word.

So:

• veður = weather
• veðrið = the weather

Since English normally says the weather, Icelandic also uses the definite form here.

Because veðrið is a neuter singular noun, and the comparative adjective has to agree with it.

The adjective is from góður (good), whose comparative is betri. But in actual use, it changes form depending on gender and number.

Here:

• veðrið = neuter singular
• so the comparative form is betra

Compare:

• dagurinn er betri = the day is better
  masculine singular
• tíðin er betri = the weather/season is better
  feminine singular
• veðrið er betra = the weather is better
  neuter singular

So betra is correct because it matches veðrið.

Yes. It is irregular, just like English good → better.

The pattern is:

• góður = good
• betri / betra = better
• bestur / best / best = best

So this sentence uses the comparative form, not the basic adjective.

That is a very common learner question. In this fixed expression, á morgun simply means tomorrow.

You should learn it as a set phrase:

• í dag = today
• á morgun = tomorrow
• í gær = yesterday

Even though á often translates as on, you should not translate it word-for-word here. The whole phrase á morgun functions as a time adverb.

Also be careful not to confuse it with:

• í morgun = this morning

That is a very common mix-up for learners.

Yes, but it has a slightly more specific feel than just think.

giska á often suggests:

• guessing
• estimating
• making an uncertain prediction

So it works well here because the speaker is not claiming certainty about tomorrow’s weather.

Other Icelandic verbs you might also see in similar contexts are:

• halda að = think that / believe that
• ætla að = suppose / intend, depending on context
• telja að = consider / believe that

But giska á að is a very natural choice when you are making a guess.

The structure is:

• Ég = I
• giska á = guess
• að = that
• veðrið = the weather
• verði = will be / become, in the subjunctive
• betra = better
• á morgun = tomorrow

So the sentence is built like this:

I guess + that + the weather + will be better + tomorrow

This is quite close to English structure, which makes it easier to understand once you know the verb forms.

Because inside the subordinate clause introduced by að, the subject comes before the verb in the normal way:

• veðrið = subject
• verði = verb
• betra = complement

So:

• að veðrið verði betra
  that the weather will be better

This is normal Icelandic word order for a subordinate clause of this kind.

A more certain version would usually avoid the speculative feel of the subjunctive and use wording that sounds more confident.

For example, a speaker who feels more sure might say something like:

• Ég held að veðrið verði betra á morgun.
• Ég held að veðrið verður betra á morgun. in some less formal or more speech-like usage, though the standard literary language often prefers the subjunctive in uncertain contexts

But the important idea for learners is this:

• giska á already signals guessing
• verði reinforces that uncertainty

So the original sentence sounds appropriately tentative.

A rough learner-friendly guide would be something like:

yeg GIS-ka ow ath VETH-rith VER-thi BET-ra ow MOR-gun

A few important notes:

• Ég begins with a sound like yehg / yeg
• ð is like the th in this, not thin
• þ would be like th in thin, but this sentence has ð, not þ
• veðrið has the definite ending -ið, where the ð is soft
• verði also has ð, again like th in this

Pronunciation varies a bit by speaker and region, but this gives the main idea.

Only partly. A very literal translation might be something like:

• I guess on that the weather become/be-subjunctive better tomorrow

That is obviously not good English.

So it is better to understand the Icelandic by phrases and grammar, not word by word:

• Ég giska á = I guess
• að = that
• veðrið verði betra = the weather will be better
• á morgun = tomorrow

That gives you the natural meaning without forcing an unnatural literal translation.