Σήμερα δεν έχει καύσωνα, αλλά η υγρασία είναι τόσο μεγάλη που κουράζομαι γρήγορα.

Greek often uses έχει literally it has / there is for weather and general conditions.

So δεν έχει καύσωνα means:

• literally: it doesn’t have heatwave
• naturally: there isn’t a heatwave / it’s not a heatwave day

This pattern is very common:

• Έχει ζέστη. = It’s hot.
• Έχει κρύο. = It’s cold.
• Έχει αέρα. = It’s windy.
• Έχει κίνηση. = There is traffic.

The negative particle δεν goes directly before the verb:

• δεν έχει

Because καύσωνα is the accusative singular form of the noun ο καύσωνας.

Greek nouns change form depending on their role in the sentence. After έχει, the thing that there is / it has normally appears in the accusative:

• ο καύσωνας = nominative
• τον καύσωνα = accusative with article
• καύσωνα = accusative without article

So:

• Έχει καύσωνα.
• Δεν έχει καύσωνα.

This is very normal after έχω.

In Greek, after έχει with weather or general conditions, the noun often appears without an article when you mean the condition in a general sense.

So:

• έχει καύσωνα = there is a heatwave / it’s heatwave-like
• έχει ζέστη = it’s hot
• έχει υγρασία = it’s humid / there is humidity

If you add the article, the meaning can become more specific:

• Έχει τον καύσωνα που είχαν προβλέψει. = There is the heatwave they had predicted.

But in your sentence, it is general, so no article is the natural choice.

They are related, but not the same.

• ζέστη = heat, hot weather, very general
• καύσωνας = heatwave, a stronger and more specific idea

So:

• Έχει ζέστη can mean it’s hot
• Έχει καύσωνα means something more extreme, like there’s a heatwave

Your sentence says that it is not a heatwave, but the humidity is still so high that the speaker gets tired quickly.

Because υγρασία is a feminine noun.

In Greek, adjectives must agree with the noun they describe in:

• gender
• number
• case

Here:

• η υγρασία = feminine singular
• so the adjective must also be feminine singular: μεγάλη

Compare:

• ο καύσωνας είναι μεγάλος = masculine
• η υγρασία είναι μεγάλη = feminine
• το πρόβλημα είναι μεγάλο = neuter

τόσο ... που is a very common Greek structure meaning so ... that.

In your sentence:

• τόσο μεγάλη = so great / so high
• που κουράζομαι γρήγορα = that I get tired quickly

So the pattern is:

• τόσο + adjective/adverb + που + result

Examples:

• Είναι τόσο αργός που με εκνευρίζει. = He is so slow that he annoys me.
• Μιλάει τόσο γρήγορα που δεν καταλαβαίνω. = He speaks so fast that I don’t understand.

This is one of the most useful result clauses in Greek.

Greek often expresses this idea with the noun υγρασία = humidity.

So instead of saying:

• it is very humid

Greek very naturally says:

• η υγρασία είναι μεγάλη = the humidity is high

Both ideas exist in Greek, but this noun-based phrasing is very common and sounds natural in everyday speech.

You may also hear:

• Έχει πολλή υγρασία. = There’s a lot of humidity / It’s very humid.

Because κουράζομαι means I get tired / I become tired, while κουράζω usually means I tire someone / something out.

Compare:

• κουράζω = active, transitive
  Η ζέστη με κουράζει. = The heat tires me.
• κουράζομαι = middle/passive form, in everyday meaning I get tired
  Κουράζομαι γρήγορα. = I get tired quickly.

So in your sentence, the speaker is talking about their own state, not directly saying the humidity tires me, even though that is the cause.

A very close alternative would be:

• ...που με κουράζει γρήγορα. = ...that it tires me quickly But κουράζομαι γρήγορα sounds more like I tire easily / I get tired quickly.

Formally, it is in the middle/passive set of endings, but in meaning it is not always truly passive in the English sense.

This is very common in Modern Greek. Many verbs appear in this form and have an everyday meaning that is just lexical, not literally passive.

So here:

• κουράζομαι does not mean I am being tired
• it means I get tired

Other similar examples:

• φοβάμαι = I am afraid
• θυμάμαι = I remember
• λυπάμαι = I am sorry / I feel sorry

So it is best to learn κουράζομαι as its own common verb meaning to get tired.

Greek uses the present tense here for a current, real situation and for a general immediate result.

• Σήμερα δεν έχει καύσωνα = Today there isn’t a heatwave
• η υγρασία είναι... = the humidity is...
• κουράζομαι γρήγορα = I get tired quickly / I’m getting tired quickly

The present tense can describe:

• what is happening now
• what is generally true in the current situation
• a repeated effect

So κουράζομαι γρήγορα can mean either:

• I get tired quickly in these conditions or
• I’m getting tired quickly right now

Greek present tense is flexible in exactly this way.

αλλά means but.

It links two contrasting ideas:

• δεν έχει καύσωνα = it is not a heatwave
• αλλά η υγρασία είναι τόσο μεγάλη... = but the humidity is still so high...

So the contrast is:

• the temperature may not be at heatwave level,
• yet the humidity still causes discomfort.

This is a very standard coordinating conjunction in Greek.

Yes, Greek word order is more flexible than English, although some versions sound more natural than others.

The given sentence is very natural:

• Σήμερα δεν έχει καύσωνα, αλλά η υγρασία είναι τόσο μεγάλη που κουράζομαι γρήγορα.

You could move some parts for emphasis:

• Δεν έχει καύσωνα σήμερα, αλλά η υγρασία είναι τόσο μεγάλη που κουράζομαι γρήγορα.
• Η υγρασία είναι τόσο μεγάλη σήμερα που κουράζομαι γρήγορα.

But the original order is good because:

• Σήμερα sets the time right away
• δεν stays before the verb
• γρήγορα comes naturally after κουράζομαι

So yes, word order can change, but the original is a very idiomatic neutral version.

It modifies κουράζομαι.

So:

• κουράζομαι = I get tired
• γρήγορα = quickly

Together:

• κουράζομαι γρήγορα = I get tired quickly

This is a basic adverb use. The adjective is:

• γρήγορος / γρήγορη / γρήγορο = quick

The adverb is:

• γρήγορα = quickly

This is very common in Greek: the neuter plural / adverbial form often functions as an adverb.

Yes. A very natural alternative is:

• Σήμερα δεν έχει καύσωνα, αλλά η υγρασία είναι τόσο μεγάλη που με κουράζει γρήγορα.

That means:

• ...but the humidity is so high that it tires me quickly.

The difference is mainly perspective:

• κουράζομαι γρήγορα = focus on my reaction/state
• με κουράζει γρήγορα = focus on what the humidity does to me

Both are correct and natural. The version in your sentence is slightly more centered on the speaker’s experience.