Leaked and invented plans for an invasion of Iraq continue to flow in the US. Any invasion will be preceded by the air movement of troops and equipment to the Persian Gulf. These is a chance that the attack could come with no such warning, using aircraft and Special Forces troops in the Gulf. In any event, the most likely time to conduct such a war is the Winter (November-March), when the heat is low enough to minimize heat exhaustion casualties. But this is not an absolute, you could go in at any time. Military operations have regularly been conducted in the hot seasons.