Nautae e portu cras proficiscentur, si tempestas bona erit.

Here nautae means the sailors.

The ending -ae is the nominative plural ending of a first-declension noun. Since nautae is the subject of proficiscentur, it has to be in the nominative plural:

• nauta = sailor
• nautae = sailors

So Nautae ... proficiscentur means The sailors ... will set out.

In Latin, grammatical declension and biological sex do not always match in the way an English speaker might expect.

Nauta is a first-declension masculine noun. That is completely normal for certain words referring to male professions or roles, especially ones borrowed from Greek or formed in old patterns. Other examples include:

• agricola = farmer
• poēta = poet
• pirāta = pirate

So even though nauta uses first-declension endings, it is usually masculine in meaning.

Portu is ablative singular.

It appears after the preposition e meaning out of or from, and e/ex takes the ablative case. So:

• e portu = out of the harbor / from the harbor

Why not portum? Because portum is accusative singular, and that would not be used after e/ex.

Also, portus is a fourth-declension noun:

• nominative singular: portus
• accusative singular: portum
• ablative singular: portu

Both e and ex mean the same thing here: out of or from.

Latin often uses:

• ex before vowels or sometimes for clarity/emphasis
• e before many consonants

But in practice, authors may use either form, and the difference is usually not important in meaning.

So e portu and ex portu would both mean from the harbor.

Proficiscentur means they will set out, they will depart, or they will set off.

It looks passive because it has passive endings, but the verb proficiscor is deponent. A deponent verb:

• has passive forms
• but active meaning

So:

• proficiscor = I set out
• proficisceris = you set out
• proficiscitur = he/she/it sets out
• proficiscentur = they will set out

Even though -ntur often suggests passive, here it is not passive in meaning.

It is future tense, third person plural.

So it means they will set out.

The future marker here is part of the future form of a third-conjugation deponent verb. For learners, the important thing is simply to recognize:

• proficiscuntur = they are setting out / they set out
• proficiscentur = they will set out

Because the sentence is talking about a future condition:

• si tempestas bona erit = if the weather is good / more literally, if the weather will be good

Latin often uses the future indicative in both parts of this kind of condition when the situation is genuinely future:

• main clause: proficiscentur = will set out
• si clause: erit = will be

This is a very normal Latin way to say a future more vivid condition.

English often prefers if the weather is good, using a present tense in the if clause, but Latin commonly uses the future: si ... erit.

Si means if.

The sentence has two parts:

• Nautae e portu cras proficiscentur = The sailors will set out from the harbor tomorrow
• si tempestas bona erit = if the weather is good / will be good

Together: The sailors will set out from the harbor tomorrow, if the weather is good.

This is a straightforward future condition:

• condition: if the weather is good
• result: the sailors will depart

Because it agrees with tempestas, which is a feminine noun.

In Latin, adjectives must agree with the nouns they describe in:

• gender
• number
• case

Here:

• tempestas is feminine singular nominative
• so the adjective must also be feminine singular nominative
• therefore: bona

So tempestas bona means good weather or more literally the weather [which is] good.

It is nominative singular.

That is because tempestas is the subject of erit in the si clause:

• tempestas = weather
• erit = will be

So the structure is:

• tempestas bona erit = the weather will be good

Since tempestas is the subject, it is nominative, and bona matches it.

Latin word order is much freer than English word order.

Cras means tomorrow, and its placement here is natural, but not the only possibility. Latin often arranges words for emphasis, rhythm, or style rather than following a fixed English-like order.

This sentence could be rearranged without changing the basic meaning, for example:

• Nautae cras e portu proficiscentur
• Cras nautae e portu proficiscentur

The version given is perfectly normal. The important thing is to identify the grammatical roles by endings, not just by position.

Either can work.

More literally:

• e portu = out of the harbor

But in smooth English, you might often say:

• from the harbor

The Latin preposition e/ex strongly suggests movement out from within something, so out of the harbor is a little closer to the Latin image. But from the harbor is often the most natural English translation.

Yes. Latin could also say:

• Si tempestas bona erit, nautae e portu cras proficiscentur.

That would mean the same thing: If the weather is good, the sailors will set out from the harbor tomorrow.

Latin allows either order. Putting the si clause first may make the condition feel more prominent, but the grammar and meaning remain the same.