Answer:
An omen suggesting a tragic end to the battle.
Step-by-step explanation:
William Shakespeare's "The Tragedy of Julius Caesar" revolves around the fight for supremacy and power of Rome from the murder of Julius Caesar to the eventual establishment of the Second Triumvirate. The conspirators of the murder of Caesar were also killed in the end.
The give excerpt is from Act V scene i of the play, where Octavius and Antony had met with Cassius and Brutus. The former two had met them on the battleground but decided to talk before the actual fighting. The conversation could not be successful as both sides do not want to surrender nor admit their wrong. Instead, they are more bend on fighting and seeing who emerges victorious.
This dialogue by Cassius about a storm going up acts as an omen for the tragic ending that the battle will bring.