What's wrong with my hand?

Sounds like it might be a bike fit issue. Have you had a professional bike fit done?

Yes but I was 60 pounds lighter so enough has changed to warrant a new fitting.

could also be that you have a slightly pinched nerve in your neck or shoulder.

Lets keep things simple.

You just started riding again, you may have a death grip on the bars. Relax, and move your hands around every couple minutes. You are probably putting extra force on your hands right now because of the extra weight. As you drop weight and your core strength increases, there will be less force on your hands.

I agree with the above. I just bought a road bike. While my fit may not be perfect.....it's not awful. I rode 3:20 on the tri bike last Saturday with no numbness. If I don't move my hands around on the road bike, they'll go numb in a few miles.

I think it's just a matter of getting used to the new position(s). My fit actually feels really good.

It was happening to me a lot. But, the more I rode and the more I moved my hands around it started to go away. Just keep riding and keep moving your hands around.

I wasn't using padding on my aero bars when I first started long trainer rides. I lost them in a bike accident and was too lazy to order a new set at the time. After a month or so, I would lose the dexterity in my left thumb. I wasn't able to pinch anything the majority of the time. Once I put the new padding on the aero bars, problem resolved itself within a day or so.

Just my .02

I'd go with the group on this and it's probably just a bit of death grip on the bars. Try some padded gloves, move your hand position around a bit.

I've had 2 different issues:
1. Riding on the hoods on my road bike, I sometimes get numbness in two fingers that goes away when I take the pressure off.
2. When I first got my tri bike, I had too aggressive a fit with my aerobars too low. After a long ride of around 50 miles, I had weakness in my left hand that gradually came back after several weeks. This was due to problems in my neck. I have since changed to a MUCH longer stem so I don't have to tilt my head back as far to see up the road. I changed to my current stem after several iterations of trying progressively longer stems. I ended up with the longest that would fit to correct the problem.

Many thanks to everybody for the input! Going to start experimenting with the fit, bought some gloves with more padding (not suggested here but figure it wouldn't hurt), and focusing on the run until the strength comes back in the hand.

I really appreciate all of the input! My girlfriend was worrying and wanting me to go to the doctor, but I don't think that's necessary.

Give the bike a rest for a couple of days to a week.

Don't let your hand get that bad again, wiggle your fingers while you ride if your feeling any tingling or numbness keep them moving until it goes away.

FYI- gloves can make it worse, I actually have no issues without gloves but when I used gloves I have some. The reason I use gloves is for group rides, you never know what's going to happen in a group ride and if I go down the glove will save some skin.

Be careful with the gloves. Especially if you have gained some weight and the gloves are a little snug, they can create pressure points that cause problems for you. Try different brands if you can. I have a few different pairs of gloves, 2 are great but one of them sucks. Not sure why I haven't thrown them out, but every time I put that pair on my hands start to go numb.

Interesting note on the gloves, thanks for sharing. The gloves have helped quite a bit with wrist pain, and overall ride comfort so far, I hadn't considered the gloves could be contributing. My hands tend to sweat a lot so without gloves it's hard to keep a good grip in the handlebars and my hands slip a lot.

I'll experiment with some different gloves.