يوم الانتقال اليوم.

Because Arabic often leaves out the present-tense verb to be.

So in a sentence like يوم الانتقال اليوم, Arabic does not need a separate word for is. The meaning is understood from the structure.

This is very common in Modern Standard Arabic:

• الجو جميل = The weather is nice
• الاجتماع غدًا = The meeting is tomorrow

If you wanted past or future, Arabic would usually use an actual verb, such as كان or سيكون.

They are related, but they are doing different jobs.

• يوم means day
• اليوم usually means today

In this sentence:

• يوم الانتقال = moving day or the day of the move
• اليوم = today

So one day word is part of the noun phrase, and the other is the time expression.

It is an iḍāfa construction, often called a genitive construction or X of Y structure.

Here:

• يوم = day
• الانتقال = the move / moving / relocation

Together, يوم الانتقال literally means day of the move.

This is how Arabic often expresses ideas that English might turn into a compound noun, like moving day.

Because in an iḍāfa construction, the first noun normally does not take الـ.

So Arabic says:

• يوم الانتقال

not:

• اليوم الانتقال

The whole phrase can still be definite because the second noun, الانتقال, is definite. In other words, the definiteness of the whole phrase comes from the second part.

A very useful fully vocalized reading is:

يومُ الانتقالِ اليومَ

Here is why:

• يومُ is nominative, because it is the topic or subject of the sentence
• الانتقالِ is genitive, because it is the second term of the iḍāfa
• اليومَ is often understood as an adverbial expression of time, so it is accusative

In normal Arabic writing, those short vowels are usually not written, so learners just see:

يوم الانتقال اليوم

Not always.

الانتقال is a verbal noun meaning something like:

• moving
• relocation
• transfer
• transition

In the right context, it can absolutely mean moving house or moving to a new place, but the word itself is broader than that. The exact meaning depends on the situation.

It is understandable and grammatically fine, but many speakers would also naturally say:

اليوم يوم الانتقال

That version puts today first, so it feels like:

• Today is moving day

Your sentence, يوم الانتقال اليوم, puts moving day first, so it feels more like:

• As for moving day, it is today

Both are possible. The difference is mostly one of emphasis and information order.

Usually, no.

In simple present-tense nominal sentences, Arabic normally does not need a word for is, and it also does not need هو here.

So:

• يوم الانتقال اليوم

is enough.

You may sometimes see or hear هو used for emphasis or clarity in some structures, but for a learner, the version without هو is the basic and most important pattern to know.