"As the weather's cooled off, so have the number of new vendors listing their homes for sale," Kennedy said.
Only 708 properties in Auckland and Northland were listed with Harcourts last month, compared to 745 in June last year.
The number of new auction listings fell 16.2 per cent, from 357 last June to just 299 last month.
"Low stock levels continue to be the main driver in pushing prices up," he said.
NIWA reported the wettest June hour across Auckland late last month, leaving motorists stranded in their cars, workers trapped in a building and many houses and businesses flooded.
However, in other parts of New Zealand the ski season is delayed and warmer than usual temperatures have been reported.
Snow is likely these school holidays, with the MetService forecasting an approaching front to bring a wintery blast to many parts of the country.
Kennedy's comments come as the Real Estate Institute of New Zealand is about to release its national sales data for June, revealing what happened last month with prices and volumes.
He indicated buyers were becoming increasingly desperate to find a place because if they were looking during the coldest months, they were likely to be extremely keen.
"Those buyers that are out there looking at this time of the year tend to be highly motivated. And with dropping stock levels, there is plenty of competition that can only lead to great results for vendors," he said.
Harcourts' average house prices for Auckland and Northland was $826,045 last June but hit $909,733 last month, up 10 per cent annually.
Harcourts has 190 agencies and more than 1900 sales consultants throughout New Zealand.