There is a Turk army headed for the kingdom, but the question is, which part of the kingdom do they plan to attack. The court continues to receive conflicting reports from different local leaders, each fearing his own land is about to be overrun with Turks. One Senator got a letter saying that "a hundred and seven galleys (ships)" are on the way, a second senator has heard 200, and the Duke's letter says "a hundred and forty."
Even more problematic, the first reports call Cyprus the target of the army, but later reports claim the Turks are heading for Rhodes. When one of the sentators points out that the Turks are more likely to want Cyprus, the Duke makes the decision that the Turks will attack Cyprus and that any move toward Rhodes is a trick. That's why he sends Othello to Cyprus.