1. Why is the evacuation order being issued now?
When the State Department issues evacuation orders, it's often not to prepare for war, but to prevent hostage-taking. Iran is currently on the brink, suffering from inflation and unrest (aftereffects of the so-called '12-day war'). Tehran has already started massive internet shutdowns and mass arrests. The U.S. fears that if a low-intensity strike (such as a cyberattack or drone assassination) occurs in the coming days, Iran might retaliate by taking American citizens inside the country hostage.
2. The 'substitution effect' of air bases
The current absence of aircraft carriers is indeed a hard limitation. However, don't forget that the U.S. military has recently had frequent movements of B-52 and B-2 bombers at Al Udeid Base in Qatar and Dafra Base in the UAE. If Trump aims for a 'one-time surgical strike,' such intercontinental bomber strikes do not require carrier support.
3. Trump's 'psychological warfare' strategy
From the 'Midnight Hammer' of 25 years to the capture of Maduro in early 26 years, this government's style is 'extremely unpredictable.' The evacuation order itself may be part of the 'absolute determination' action, aimed at creating panic, in conjunction with domestic protests in Iran, attempting to cause internal instability or even defection within the Iranian regime.
The United States will not send ground troops or conduct large-scale bombings. The most likely operation is to paralyze Tehran's surveillance system using cyber warfare, or to use drones/missiles to strike military communication command centers.
This tactic does not require an aircraft carrier group to be stationed for long periods; a single wave can 'hand a knife' to the domestic opposition.
The United States will first use stealth bombers or cyber warfare for a 'starter' strike while waiting for the deployment of the USS George H.W. Bush.