Unfortunately, there are a host of other variables, other than your height and weight, that are needed to produce a worthwhile number. Your bike set-up, position, the course undulations and wind and air pressure conditions on the day are just a few key ones.
Even in the relatively controlled conditions of a velodrome, to find the power required to hold a given speed, you need more metrics than height and weight. Fortunately though, if you’re willing to do some number digging and can get hold of a .gpx file of the course and don’t mind spending $19 per month, Best Bike Split should be able to get you the number you’re looking for.
What's the difference between average power and normalised power on the bike?
Is it worth calculating what wattage you need to maintain a certain cycling speed?
However, before you sign up and start number crunching, as a coach, I’d question the value of such a target from a motivational perspective and whether you’re trying to do things the wrong way round. If the number it throws at you is way above, or even way below, what you’ll be able to achieve, what affect will that have on you? Personally, I would do a solid winter of training and take that into the spring and summer. Then by your A-race you should know from training and B races what power you’ll be able to sustain, irrespective of what you’d like to be able to do. At that point, you could then use Best Bike Split to predict your expected time.