"From January onwards, we will start seeing the cumulative affects."
A restricted fire season is in place for the rural areas meaning fires can't be lit in rural areas unless a permit has been granted by the council. He said fire permits were still being issued as normal, although, depending on how dry it got, they may be stopped.
Mr Horn said he was advising people in the Rotorua district to light fires only if they really needed to, notify neighbours, and not to burn after dark.
"I'd suggest that's a good idea for the urban area as well."
He said people also needed to make sure fires were fully extinguished.
"If people see anything out of the ordinary, they should phone 111. We would rather people phone, and will respond accordingly."
Mr Horn said Rotorua people had been responsible when it came to lighting fires over the past couple of months.
"I'm pretty happy at the moment."
The last time Rotorua saw El Nino conditions was the 1997/98 summer, which was one of the worst fire seasons, with fire crews responding to callouts on an almost daily basis.
Mr Horn said it was too soon to say whether a total fire ban would be put in place.
"It's definitely a possibility as we start getting drier and drier. We've had quite a few of them over the past five or so years - not necessarily for a long period of time."