Why does smoke come from radiator after raining?

I have a 1999 Subaru Legacy Outback with 106,534 miles on it, deal. Well last week it rained pretty hard here in Chicago for a few days. I started the car and drove around for about 15 minutes before I noticed smoke coming from the hood sides and front. I pulled over and didn't turn off the car to see what was going on and I saw smoke coming from the top right (viewed from the driver seat) corner of the radiator. I took it to my mechanic and he looked at it and said it could either be the water evaporating or a super tiny leak in the radiator but that I could still drive it pretty much until the radiator breaks. I had called another well trusted mechanic and he told me not to worry about it as long as I didn't see anything leaking then it was definitely just water evaporating. It is raining right now and smoke is coming out again, is it really just water evaporating? Last weekend (3 days ago) I drove from Chicago to Blue Mound, WI, about 270 miles altogether to get there and back. It was raining during the drive back but I didn't notice any smoke coming out then. I wouldn't say that I personally beat the car up, I've only had it for 3 weeks. I had a 1999 Ford Ranger before I got this and the Ranger had the whole bottom radiator exposed since I didn't have a front bumper on it but it never smoked. I have never owned a car before and I don't know if this only happens to Subarus. It's raining right now and there's smoke coming out again, it rained hard all morning too.

Have the coolant system pressure checked. That will indicate whether or not you have any leaks.

The coolant exiting the engine can get over 200 degrees, which can heat to top of the radiator and easily evaporate the rain.

Sounds like rain water hitting the hot radiator.

Your second mechanic is most likely the correct one - its not smoke its steam

Duh.

It isn't smoke. It's steam. Water hitting hot pipes makes steam.

Steam not smoke, get it right dummy

There's a difference between steam and smoke, dumbass, so learn it. Once you're sure its steam and not smoke come back and ask an intelligent question.

"… But that I could still drive it pretty much until the radiator breaks."

is the statement of an idiot, not a mechanic!

If I was you, I'd be checking my coolant reservoir regularly, to see if any coolant is disappearing.

Check the water temperature manual
or use a laser spot temp.Test