Days of dry and windy weather have made conditions challenging for fire crews and volunteers tackling flames burning across peatland moors and in woodland.
McCook said residents in Nethy Bridge hoped a change in the weather would help efforts to tackle remaining hotspots.
He said: “The overnight and continuing rain today will undoubtedly make a huge difference to the firefighting.”
McCook added: “There is a distinct smell of smoke around but that will be from the rain and lack of wind.”
CNPA said the Scottish Fire and Rescue Service (SFRS) reported on Monday evening there had been a reduction in visible flames, but warned large areas were still smouldering.
The park authority said the fire was still burning deep in the peat soil.
It added that helicopters, sourced and funded by Forestry and Land Scotland, would likely continue water bombing on Tuesday, assisted by drones equipped with thermal cameras to detect hotspots.
The fire broke out near the village of Glenmore, outside Aviemore, on 15 July and led to residents and campsites being evacuated.
At its height, more than 500 firefighters were involved in the response and Police Scotland declared it a “major incident” on Friday.
