I think we hear since CoT that a storm is coming. It's certainly figuratively meant for the Shadowspawn attack from the Blight and TG in general (a figurative "monster storm" ). However, besides this attack of the Shadow's forces, I believe we can expect that a real monster storm will yet badly hit all the Westlands. An unnaturally powerful storm with hail, lightnings and strong winds causing floods, which will kill thousands of people & animals, and destroy buildings & plants.

We know that the DO can influence the weather. In almost all PoV in TGS the strangely overcast sky is mentioned, which hides the sun and lowers the spirits of many men. Plus, Nynaeve tells in KoD, after she Listened to the Wind: "That a storm is coming. A terrible storm." She repeats her dire warning in TGS, ch.7. Such unnatural storms - but not as destructive - were also seen at SG, above Caemlyn in KoD and in the Borderlands in the prologue of TGS.

In my view, this last monster storm is also mentioned in various Prophecies:
Egwene has "a dream of a storm, great dark clouds rolling without wind or rain while forked lightning bolts, every one identical, rent the earth."

From the Prophecies of the Dragon:
"Storms rumble beyond the horizon, and the fires of heaven purge the earth. There is no salvation without destruction, no hope this side of death."

"The seas rage, and stormclouds gather unseen."

"Master of the lightnings, rider on the storm, wearer of a crown of swords, spinner-out of fate. Who thinks he turns the Wheel of Time, may learn the truth too late."

"And it shall come to pass, in the days when the Dark Hunt rides, when the right hand falters and the left hand strays, that mankind shall come to the Crossroads of Twilight and all that is, all that was, and all that will be shall balance on the point of a sword, while the winds of the Shadow grow."

Perhaps Perrin's Dream:
"Rand stood amid swirling stormwinds, laughing wildly, even madly, arms upraised, and on the winds rode [dragons]." (though this Dream most likely refers to the end of TGS with Rand on Dragonmount, almost destroying the world and experiencing his previous lives)

Finally from a 4th Age text:
"And what was once did come again - in fire and in storm -splitting all in twain."

And the poem:
"We rode on the winds of the rising storm,
We ran to the sounds of the thunder.
We danced among the lightning bolts,
and tore the world asunder."

In my view, this final monster storm will announce the beginning of TG and be accompanied by black clouds, which will permanently and completely darken the world to destroy mankind's last hope.