Ah yes, I can see many people flocking to this poem because it is so short then backing away because it is too short to speak of. However, this tiny poem, with a grand total of 21 words, 22 if one includes the title, speaks much louder than many other poems I have seen. Have I gone crazy? Probably, but such tiny poems are very much worth looking at.
When I think of a fog, I think of two things, either someone in a state of contemplative confusion, or that nice little meteorological phenomenon that hinders one's sight. Generally, both of these things creep in very quietly, and when they hit you, there is no question that they are there. This is very much akin to the speaker saying that "fog comes on little cat feet." Kittens, much likes their grown up cat counterparts, will always move with a sudden silence, and you may very well turn around and be startled to see them there, but sure enough, they are. The speaker draws a very true comparison.
"It sits looking over harbor and city on silent haunches and the moves on." This was the most literal sentence I have ever seen in a poem, until I thought about it for a little bit. The fog is looking at something, obviously. In this case, it would be a city, or a harbor. Once again, obvious. But why is it looking at the city? Say the fog has more than just cat feet as much as it has a cat's curiosity as well. I would say that, much like a cat does when looking out a window, the fog is watching the entire landscape curiously and very attentively by covering up the entire area of it's viewing. Fogs do happen to linger around for a little bit, especially in the mountains, where part of the fog will literally get caught in the trees on the mountainside. But this poem does not discuss mountains, it discusses a city and a harbor, and there is much more to look at there.
Let us take a step away from the literal meaning of the poem. A fog, at least in my mind when I experience one, is a state of contemplative confusion. I am thinking about things, as I do too terribly often according to some, and suddenly I hit a rut, and everything stops. Suddenly my other thoughts are blurred. Maybe I am distracted by something that I didn't expect, or maybe something came up that broke my train of thought completely, leaving me no place to pick up the pieces and start again. I guess a good was to describe a "fog" is to either call it a "mental rut", or as one of my teachers loves to put it, "an extended brain fart."
So, why do fogs stay over a certain area for a certain amount of time? Is the fog the docile fellow who mindlessly moves over the city, or is he the mischievous little devil that causes ships to blow their fog horns at the harbor and drivers to curse their way across the street because their fog lights aren't working? Personally, I'd like to think the latter, all things considered. What wrongs can fogs do in a city? What will happen if the passage of light is blocked and everyone is left in a blur. I've seen people walk into telephone poles because fog was hindering their view. I've seen cars crash into each other because they couldn't figure out where the street lines were due to the fog. I've heard of boats running into bridges or other boats because of fog. But it doesn't actually do any of this, rather, it is just it's presence that makes all of these things happen. It is almost as if people are staring at the fog in awe of it's omnipresent presence, even if they have no choice not to because that is all that they can see.
But is the fog such an evil fellow? I do not believe so. I think it's just a mischievous child who thinks certain things are funny. Yes, children like the good old fashioned Wile E Coyote slamming into a cliff, so I guess the fog enjoys watching cars and boats run into each other in the harbor and in the city. It's presence brings chaos to these places. And even though the fog doesn't mean to do these things, it certainly enjoys watching them.
However, much like a child, the fog will get bored with seeing the same things over and over again. So of course, much like the child does, the fog will move on and away to elsewhere just as quickly as it appeared.
This poem contains no sappy of feelings or incredibly deep messages that I will carry for the rest of my days. However, it does present something that many poems, and many other things for that matter don't. It presents to me a new and interesting way at looking at an act of nature that is almost an everyday occurrence. See, not all poems have to be driven by conventional ways of thinking.
Take one step back and read some good poetry.
If you have low expectations, go here and be happy.