אל תפתחי את המכסה עכשיו; הקומקום חם מאוד.

In Hebrew, אל is commonly used for a negative command: don’t ...

So:

• אל תפתחי = don’t open (said to one female)
• לא תפתחי would usually not be the normal way to give a command

A useful shortcut:

• לא = ordinary negation, not
• אל = negation in commands, don’t

תפתחי is the 2nd person feminine singular future form of the verb לפתוח (to open).

In Hebrew, negative commands are often formed with:

• אל + future form

So:

• אל תפתחי = don’t open (to one woman/girl)
• אל תפתח = don’t open (to one man/boy)

The ending -י here signals that the speaker is addressing a female singular.

You would say:

• אל תפתח את המכסה עכשיו; הקומקום חם מאוד.

Only תפתחי changes to תפתח.

If you were speaking to more than one person, the verb would change again:

• to a group of males or a mixed group: אל תפתחו
• to a group of females: in modern everyday Hebrew, people often also use אל תפתחו, although older/more formal grammar distinguishes feminine plural forms

את is the direct object marker. It appears before a definite direct object.

Here:

• המכסה = the lid
• because it is definite (the lid), Hebrew uses את

So:

• תפתחי את המכסה = open the lid
• but with an indefinite object, you usually would not use את

For example:

• פתחי מכסה would be something like open a lid or open any lid, and that sounds different

Important: את does not mean the and does not get translated into English directly.

The prefix ה־ is the Hebrew definite article, meaning the.

So:

• מכסה = a lid / lid
• המכסה = the lid

The same thing happens with הקומקום:

• קומקום = kettle
• הקומקום = the kettle

Hebrew usually attaches the directly to the noun as a prefix.

מכסה is generally treated as a masculine noun, even though it ends with ־ה, which often looks feminine to learners.

That is important because adjectives and verbs may agree with the noun’s grammatical gender in some contexts.

Hebrew has quite a few nouns whose gender is not obvious from the ending, so this is something you often just have to learn word by word.

In present-tense Hebrew, there is usually no separate word for is / am / are.

So:

• הקומקום חם מאוד literally looks like:
• the kettle very hot

But it means:

• the kettle is very hot

This is completely normal in Hebrew.

Compare:

• המים קרים = the water is cold
• הילד עייף = the boy is tired

No present-tense is is needed.

Because קומקום is a masculine singular noun, the adjective must match it.

So:

• קומקום חם = a hot kettle
• הקומקום חם מאוד = the kettle is very hot

If the noun were feminine singular, you would usually use חמה:

• הכוס חמה = the cup is hot

So this is a case of normal adjective agreement:

• masculine singular: חם
• feminine singular: חמה

מאוד means very.

In this sentence:

• חם מאוד = very hot

Hebrew often places מאוד after the adjective:

• יפה מאוד = very beautiful
• גדול מאוד = very big
• חם מאוד = very hot

That word order is very natural in Hebrew.

עכשיו means now.

In this sentence:

• אל תפתחי את המכסה עכשיו = don’t open the lid now

Its placement is natural, but Hebrew word order is somewhat flexible. You could move עכשיו for emphasis in some contexts, for example:

• עכשיו אל תפתחי את המכסה
• אל תפתחי עכשיו את המכסה

These all mean roughly the same thing, but the emphasis shifts slightly. The version in your sentence sounds smooth and neutral.

The semicolon links two closely related statements:

• אל תפתחי את המכסה עכשיו
• הקומקום חם מאוד

So the second clause explains the first one:

• Don’t open the lid now; the kettle is very hot.

In everyday writing, many people might also use a comma or split this into two sentences. The semicolon just shows a clear connection between the warning and the reason.

A simple pronunciation guide is:

Al tift’chi et ha-mich-se aḵ-shav; ha-kum-kum kham me-od.

A few notes:

• אל = al
• תפתחי = tift’chi
  The ch here is the throaty sound in Hebrew, not the English sound in chair.
• המכסה = ha-michse or ha-mikhse, depending on accent/transliteration style
• עכשיו = akhshav
• הקומקום = hakumkum
• חם = kham
• מאוד = me’od

Stress is typically:

• tift’CHI
• akhSHAV
• me’OD

Not exactly in form, but yes in function.

Hebrew has true imperative forms, but in modern Hebrew, especially in negative commands, speakers very often use:

• אל + future

So although תפתחי is formally a future-tense form, in this sentence it functions as a command:

• אל תפתחי = don’t open

This is very common and very natural.

Yes. You could say:

• אל תפתחי את המכסה עכשיו, כי הקומקום חם מאוד.

That means:

• Don’t open the lid now, because the kettle is very hot.

Your original sentence is a little more compact and direct. Both are natural. The version without כי sounds like a warning followed immediately by the explanation.