هاي المهارة مهمة.

هاي means this and is used with a feminine singular noun in Levantine Arabic.

Here it points to المهارة because مهارة is feminine.

You may also hear other regional forms such as هيدي or هادي, depending on where the speaker is from.

Because مهارة is a grammatically feminine noun.

A very common clue is the ending ة. Nouns ending in ة are often feminine, and that affects other words around them.

So because مهارة is feminine:

• هاي is feminine
• مهمة is also feminine

Because adjectives in Arabic usually agree with the noun they describe.

Since مهارة is feminine, the adjective must also be feminine:

• masculine: مهم
• feminine: مهمة

So مهارة مهمة is the correct match.

In Arabic, the verb to be is usually not said in the present tense.

So a sentence like:

• هاي المهارة مهمة

literally looks like:

• this skill important

but it naturally means:

• this skill is important

If you wanted the past, future, or something more explicit, Arabic would use forms of كان or similar structures.

Because after a demonstrative like هاي in Arabic, the noun is usually definite.

So Arabic says:

• هاي المهارة = this skill

not usually just:

• هاي مهارة

That means the noun normally takes الـ after this/that.

Because مهمة here is the predicate of the sentence, not part of the noun phrase the important skill.

Compare these two ideas:

• هاي المهارة مهمة = This skill is important
• هاي المهارة المهمة = This important skill / this skill that is important

So in your sentence, مهمة is not marked with الـ because it is saying something about the skill.

In Arabic, adjectives normally come after the noun they describe.

So:

• مهارة مهمة = an important skill

That word order is normal in both Standard Arabic and Levantine.

In your full sentence, the adjective still comes after the noun:

• هاي المهارة مهمة

A helpful learner pronunciation is:

haay il-mahaara muhimme

In everyday speech, many speakers reduce it a bit, so you may also hear something closer to:

haay l-mahaara mhemme

A few useful notes:

• هاي sounds like high with an h
• الـ here is pronounced clearly because م is not a sun letter
• مهمة is often pronounced more like mhimme / mhemme in colloquial speech

Yes. A very common alternative is:

المهارة هاي مهمة

This also means this skill is important.

In spoken Levantine, putting the demonstrative after the noun is very natural. Both patterns are used:

• هاي المهارة مهمة
• المهارة هاي مهمة

Yes. Levantine has regional variation.

Depending on the area, you may hear:

• هاي
• هيدي
• هادي

All can mean this for a feminine noun.

So versions like these may all be heard:

• هاي المهارة مهمة
• هيدي المهارة مهمة
• هادي المهارة مهمة

They differ by region more than by meaning.

If the noun were masculine, both the demonstrative and the adjective would change.

For example:

• هاد الكتاب مهم = this book is important

Compare:

• feminine: هاي المهارة مهمة
• masculine: هاد الكتاب مهم

So Arabic changes both this and important to match the noun’s gender.