Hamilton's shock move was announced in January ahead of what will now be his 12th and final season with the Silver Arrows, bringing an end to a career-long association with the German marque.
The seven-time champion's move for next season means he will follow a path once travelled by former McLaren teammate Alonso, who raced for Ferrari between 2010 and 2014.
Casting his judgement over what has been described by Hamilton a move which fulfils a "childhood dream", Alonso told media including RacingNews365: "It was not his childhood dream 12 months ago - or two months ago - I guess, because he had a different dream.
"I hope he enjoys the experience, it is a very special team.
"It is more special when you win but that's the thing, you need to win and it is a few years already that they have a very fast car and fighting for big things... maybe Lewis can bring that extra [bit] to fight for the championship.
"The car is there. At the end of last year, even with a very dominant Red Bull car, Ferrari was still able to match the lap time and be faster than them in most of the qualifying.
"So I think the car should be fast enough."
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Mercedes to keep secrets?
Alonso was in a similar position to Hamilton back in 2006, when he had made clear his intentions to leave Renault for McLaren the following season well ahead of time.
Asked what effect taking the decision so early had on his campaign, the Aston Martin driver explained: "It was not a big difference for me.
"In 2006, I started the season very ok and relaxed with the team with a good atmosphere.
"It did change, maybe, for the team a little bit because halfway through the season, they were testing things and programming things for the following year and I was not involved in those things because they kept some secrets from me, which was understandable.
"So I think from the drivers' point of view, it doesn't change much but for the team, they try to hide a few things in the second part of the year."