The man is described as Maori, solid build, about 165cm tall, wearing black pants that change colour below the knee to a cream colour, and a light grey hoodie.
Mr Nightingale said both women described the man as either having gaps in his teeth or teeth in a poor condition.
"The behaviour of the offender is alarming and concerning to say the least and is resulting in women feeling unsafe when they are exercising. While the offending was limited to a grabbing incident, it could be an indicator of more serious offending."
Mr Nightingale wanted members of the public to be careful, particularly if on their own, and if anyone saw anything suspicious they should call 111.
"We would rather get called out to check on someone and be safe than be sorry."
Information that's not urgent can also be passed on by calling 0800 CRIMESTOPPERS.