Commercial pilot here, currently flying transatlantic routes. I avoided Irma last week while flying to Buenos Aires (it was not this big yet). I have partners in San Juan at this moment, bunkered in the hotel. We see this as a crazy move, very well executed, but too risky for the plane itself (not so much for the crew).

Let me explain, the metar and tafors (the airport meteorological reports we use) during the flight in San Juan show that the flight was doable. No crazy winds during landing, and worsening during take of but well within the limits you may find in a local thunderstorm. The predictions allowed them to see the window to fly in and out. If arriving the weather was too bad or you see the hurricane getting too close to the airport,they could have got away without landing. For take off either you have the right conditions (under the legal limits) or you don't.

What they risked IMHO is having some kind of technical problem or delay once in San Juan and having to stay there to weather the hurricane. That could mean heavy damage to the airplane while on the airport, even a total loss.

That said for me the most amazing of it all, is not the short stay at the ground. While very fast is not uncommon to see them with an experieced team, the slower part is the disembarking and embarking of the passengers, and they surely were all motivated to hurry.

The most impressive is how they followed the quite thin alley between the hurricane arms till they were clear of the bad weather. In a situation like that you only see red and magenta in your radar and a narrow black or green zone where you can fly safely. That's surely was the most scary part for them beyond the adrenalin of a fast and potentially dangerous operation.

Looks like the typical movie scene of a spaceship passing between closing doors!! Certainly brass balls.

Edit: some typos and a "don't" that I left behind and was changing the meaning of a sentence. Sorry written from the cellphone.