(BIVN) – Punctuating an already wet rainy season, a Flash Flood Watch will be in effect for all the main Hawaiian Islands this weekend starting Friday evening.

The National Weather Service in Honolulu says “deep moisture combined with increased instability associated with a developing low near the islands late Friday through this weekend will increase the risk of flash flooding.”

“Rapidly rising water levels may threaten local area streams and low lying flash flood prone areas.” forecasters say.

From this morning’s state-wide forecast discussion:

Meanwhile a sharp upper level trough west of the islands appears in the GFS 500 mb streamlines. This trough will deepen as it approaches the islands today, destabilizing the atmosphere and developing a weak surface low later tonight enhancing shower activity statewide. Both the American (GFS) and European (ECMWF) global models are showing a surface low moving across the state on Saturday. Deep tropical moisture, atmospheric instability and forcing from this upper level trough and surface low will lead to widespread moderate to heavy rainfall and probably a few thunderstorms spreading eastward across the state through the weekend. The impacts will start over the western islands through early Saturday morning and then spread eastward to Maui and the Big Island by late Saturday morning and afternoon. The onset timing of these impacts may vary a bit due to unforeseen smaller scale shower bands that may develop ahead of the main system. A Flash Flood Watch was issued across all islands starting Friday evening through Sunday afternoon due to the strong potential for heavy rain and flash flooding. We recommend postponing outdoor activities this weekend near streams and low lying flood prone areas until this flash flood threat passes.

The High Surf Warning that was in effect over the past few days has also been cancelled. A High Surf Advisory is now in effect for the Hawaii Island for the shorelines of Kohala, Hamakua, Hilo and Puna through tonight.

All roads and parks are open, however the county’s Parks and Recreation Department reports the Hilo Bay Front Canoe Halau area will remain closed until clean-up is completed.