The agency says: "River levels are above normal but flooding of property is not expected at the moment.
"Lake levels at Llyn Tegid are rising and are expected to do so for the next 15 hours.
"Further rainfall is forecast over the next 12 hours and conditions are expected to deteriorate.
"River levels at Bala and Corwen are rising and are expected to do so for the next 15 hours. In addition to the area detailed, some localised flooding problems may result from surface water."
For more information, call Floodline on 0845 988 1188, select option 1 and enter Quickdial number 192002 to get more information