first half marathon

It's a bit late to jump into a training plan. The novice plans start at much less mileage than you are currently doing, and there's no point in going backwards, while the more advanced plans require more miles than you have time to do. I assume you are currently running about 5 miles 5 days a week? Are you doing any speedwork? Don't add it if you aren't already doing it, but if you are currently doing it, do tempo runs rather than intervals. I would continue what you've been doing, but add 1 to 1.5 miles to your long run once a week. Maybe also add a bit to one of your midweek runs. Overall volume will help as much as a longer long run. You will be able to finish a half with your longest run at 8 or 9 miles, but it won't be easy.

The last week before your race cut back on your mileage, and take the day or two days before the race off or just do really short easy 2 milers. On race day you should be feeling pretty good but you will want to rein yourself in to make your energy last as long as possible. Keep your pace easy. If you are still feeling good at 10, then speed up, but don't let yourself go hard before that.

My first half I had been running weekly long runs of 10+ miles for the 6 months prior and peaked at 14. It was still a long race.

What exactly is your long run mileage now? is it 5? Or is that an example of a plan somewhere? I'm a little confused. I wouldn't want to tackle a half having never run at least 10-even that's pretty light since there's a whole 5k to go after that (and I really felt like everything after mile 8 was superfluous during the race).

You have 3 weeks to build up to long run of 10 miles, that's twice the distance you are running now. Novice HM plans mostly peak at 10-11 miles. They say if you can run 10, you can run 13.1. It's not impossible but you are risking injury and the race will feel like hell. A 10K in 4 weeks would be a perfect step-down for you. You could push yourself and enjoy the race and then build up from there for a HM.