Cat meowing at front door every morning

Hello to all! I hope someone can help. My cat (he is a little over a year and a half old), for almost a full week now, sits right up against the front door to my apartment and just cries and cries these very sorrowful meows. He seems to be so upset and even tries to jump up to the door knob and looks as though he is trying to wrap his paws around it. This will go on for about 15to 20 minutes each morning without fail. My cat has always been an indoor cat and has always lived in an apartment. My husband and I did get him as a stray cat when he was about two months old, but since then has been an indoor cat. It is breaking my heart each morning to see him so upset by the front door, so if anyone has any advice that would be wonderful.

Is he neutered? If not this could be the reason.There might be a lady in heat in teh neighbourhood.
Is there more apartments in the house?
Even if he is neutered the smell of a new cat in the house can make him curious. Has there been any changes among the neighbours the last week? New animals? New habits?
Are you home during the day so you no that he only does this in te morning?
Cats can often sence things that we can't - are your neighbours okay?

if you can't find the rason maybe a companion cat would help to keep him happy indoors.

Hello Malena. Yes, my cat is neutered. To my knowledge there have not been any changes with any of the neighbors bringing in new pets, etc. There are other apartments around us. The apartment across from us has a dog, and the apartment right above us has a cat. Both animals were at their respective apartments before we moved in, so they are not new. My cat does not exhibit this behavior in the evenings when my husband and I are home. He acts fine then. I guess I don't know for certain if he does this behavior during the day when we are both at work, but it definitely makes the mornings interesting. Thanks for your help! Keep it coming!

Here's an idea... At the pet store ask them for a 4-point harness for a S, M or L size cat - it's the kind that goes around his neck but also behind his front legs (but not the kind like an X.. the kind that the neck part and other are attached by a short piece of leather or plastic along his back). Get him into it for very short, then longer times each day around the house, and then clip on a leash (to the back piece) and take him for a walk (or rather let him take you!). Make it tight enough to just slip a finger underneath as they can wriggle out otherwise (and it won't choke him). Make it a daily thing for him and he'll be a lot happier!