You're right but It has already happened. The warning was announced 2000 years ago:
“Repent, for the kingdom of God has come near.”
"Unless you repent, you too will all perish."
And "the ark" was built:
Mark 16
15 He said to them [the apostles], “Go into all the world and preach the gospel to all creation.
16 Whoever believes and is baptized will be saved, but whoever does not believe will be condemned.
Acts 2
38 Peter replied, “Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins. And you will receive the gift of the Holy Spirit.
39 The promise is for you and your children and for all who are far off—for all whom the Lord our God will call.”
40 With many other words he warned them; and he pleaded with them, “Save yourselves from this corrupt generation.”
Titus 2
11 For the grace of God has appeared that offers salvation to all people.
12 It teaches us to say “No” to ungodliness and worldly passions, and to live self-controlled, upright and godly lives in this present age,
13 while we wait for the blessed hope—the appearing of the glory of our great God and Savior, Jesus Christ,
14 who gave himself for us to redeem us from all wickedness and to purify for himself a people that are his very own, eager to do what is good.
Ephesians 1:13
13 And you also were included in Christ when you heard the message of truth, the gospel of your salvation. When you believed, you were marked in him with a seal, the promised Holy Spirit,
14 who is a deposit guaranteeing our inheritance until the redemption of those who are God’s possession—to the praise of his glory.
Yes, an Ark was built by Jesus, when He came the first time. But there is a Prophecy, that, when Christ comes again, He will make a new covenant, meaning, a new Ark:
"This is what the LORD Almighty, the God of Israel, says: "When I bring them back from captivity, the people in the land of Judah and in its towns will once again use these words: 'The LORD bless you, you prosperous city, you sacred mountain…..The days are coming," declares the LORD, "when I
will make a new covenant with the people of Israel and with the people of Judah.” Jerm. 31:23-31
This is a Prophecy regarding End Time. It is about when, God will gather the Jews again in their Land. This already happend in late 19th century. At that time, a new covenant also was made. That, is the new Ark, that, Christ would have to make to save people, for the new Period, just as Noah made a new covenant.
And Just as When the Noah came, and warned people about an upcoming Catastrophe, so did Baha'u'llah in His Time:
"The world is in travail, and its agitation waxeth day by day. Its face is turned towards waywardness and unbelief. Such shall be its plight, that to disclose it now would not be meet and seemly. Its perversity will long continue.
And when the appointed hour is come, there shall suddenly appear that which shall cause the limbs of mankind to quake. Then, and only then, will the Divine Standard be unfurled, and the Nightingale of Paradise warble its melody."
Bahá’u’lláh: Gleanings from the Writings of Bahá’u’lláh, p. 118
This is how Jesus will fulfill judgement:
Matthew 13:49
49 This is how it will be at the end of the age. The angels will come and separate the wicked from the righteous
Yes, how would they separate the wicked from righteous? What mechanism would be used for separation?
2 Thessalonians 1
7 This will happen when the Lord Jesus is revealed from heaven in blazing fire with his powerful angels.
8 He will punish those who do not know God and do not obey the gospel of our Lord Jesus.
9 They will be punished with everlasting destruction and shut out from the presence of the Lord and from the glory of his might
10 on the day he comes to be glorified in his holy people and to be marveled at among all those who have believed. This includes you, because you believed our testimony to you.
The same was accomplished by the flood. The wicked were destroyed and the righteous Noah with his family remained:
Genesis 6
5 The LORD saw that the wickedness of man was great in the earth, and that every intention of the thoughts of his heart was only evil continually...
13 And God said to Noah, "I have determined to make an end of all flesh, for the earth is filled with violence through them. Behold, I will destroy them with the earth.
Genesis 7
1 Then the LORD said to Noah, "Go into the ark, you and all your household, for I have seen that you are righteous before me in this generation...
These verses are exactly what Baha'u'llah did.
4 For in seven days I will send rain on the earth forty days and forty nights, and every living thing that I have made I will blot out from the face of the ground."
This Seven days, and Forty Days, also, things that must happen when Christ returns, because same events that happend during Days of Noah, must also happen, during Days of Son of Man, when He comes again.
They already did come to pass.