قَالَ عَمَّا قَلِيلٍ لَيُصْبِحُنَّ نَادِمِينَ ﴿٤٠﴾

(Allah) said: "In a little while, they are sure to be regretful.''

meaning, `for their opposition towards you and their stubborn rejection of the Message you brought to them.'

فَأَخَذَتْهُمُ الصَّيْحَةُ بِالْحَقِّ ...

So, The Sayhah overtook them in truth,

meaning, they deserved that from Allah because of their disbelief and wrongdoing. The apparent meaning is that the Sayhah was combined with the furious cold wind,

تُدَمِّرُ كُلَّ شَىْءٍ بِأَمْرِ رَبِّهَا فَأْصْبَحُواْ لاَ يُرَى إِلاَّ مَسَـكِنُهُمْ

Destroying everything by the command of its Lord! So they became such that nothing could be seen except their dwellings! (46:25)

... فَجَعَلْنَاهُمْ غُثَاء ...

and We made them as rubbish of dead plants.

means, they are dead and destroyed, like the scum and rubbish left by a flood, i.e., something insignificant and useless that is of no benefit to anyone.