The former England midfielder was due to link up with the new MLS franchise at the start of this month, but instead his loan spell with Manchester City was extended until the end of the Premier League season.
Confusion reigned over whether Lampard had signed a permanent deal with New York City, but the former Chelsea man cleared up any uncertainty by confirming that he will move to the MLS in July.
New York City fans made no secret of their displeasure at the delay in Lampard's arrival, which will see the 36-year-old miss the first four months of the campaign.
Former United States international Harkes understands why supporters are disgruntled over Lampard's belated switch, but is in no doubt he will make a make a big impression when he finally arrives.
He told Perform: "You can understand why [Manchester] City would want to keep a player of the quality of Frank Lampard, who has made such a great impact coming off the bench.
"But also from the point of view of season-ticket holders, you can see why they would be unhappy having bought tickets expecting he would be there from the start of the season, so that does stink."
Harkes discovered Lampard's qualities when the West Ham academy graduate cleaned his boots during his time in the youth team at Upton Park and expects the veteran to shine during his time in the United States.
He said: "Frank Lampard has always been a great professional and he will continue to be one. He serves the game well on and off the the field, speaks intelligently. It's not just the high level he brings on the field but also off the field, he's a great ambassador the game.
"Once he does arrive it will be very exciting. It will be incredibly exciting seeing Steven Gerrard [who will join LA Galaxy in August] go up against Frank again.
"Frank I know really well, because he was my boot boy at West Ham when he was in the youth team. Him and Rio Ferdinand were there at the time and you could tell they were always going to be quality players.
"Not just with their technical ability on the the field, but also their approach to the game. It's a great mental strength they had and I think that will see him through for the next couple of years."
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