Singh admitted touching the teen over her clothes and revealed he had touched one other young woman while on the bus. Police were unable to identify his second victim.
Singh appeared in Hastings District Court yesterday for sentence on five charges of indecent assault.
His lawyer Richard Stone said Singh was remorseful and had written a letter of apology to the teen.
Singh was in New Zealand on a student visa and was likely to be deported back to India to live with his mother and sister once he had gone through the court process, Mr Stone said.
Deportation was a significant punishment as it took away any further education or job prospects in New Zealand.
"The whole (court) experience has been very traumatic for him."
Mr Stone said Singh's offending was at the lower end of the scale.
However, police prosecutor Nigel Wolland said the persistent offending against a stranger warranted a sentencing starting point of imprisonment.
Judge Bridget Mackintosh said the woman Singh had targeted was quite "resilient" and took a pragmatic view of the offending.
She obviously did not like what was going on but had no on-going emotional issues.
"She's at a loss as to how you could behave in that way to someone you don't know," Judge Mackintosh told Singh.
"You thought you were being funny and engaging but you're realising you crossed a line."
Judge Mackintosh said Singh chose an "unsophisticated way" to get the teen's attention.
"You got the attention of her of course, and the police and the court."
Judge Mackintosh said the sentencing starting point was 12 months' imprisonment.
She gave Singh credit for his guilty plea, remorse and lack of previous offending.
As there was no suitable community detention address, she sentenced him to 250 hours' community work.
Singh was given his first strike under the three strikes legislation for violent offending.
