The National Weather Service in Portland has issued a special weather statement about a potent fall storm that will set up off the British Columbia coast this weekend and bring prolonged moderate to heavy rain to Southwest Washington and Northwest Oregon. This is a highly unusual storm for September, and has the potential for producing record rain.
The first batch of rain will arrive by Friday afternoon. Between 0.75 and 2.00 inches of rain will fall by daybreak Saturday, with heaviest amounts over the Coast Range and southwest slopes of the Washington Cascades.
The jet stream gradually sags south Saturday through Monday morning, and brings a reinforcing punch of tropical moisture. This deep plume of moisture is being generated from former typhoon
Pabuk that was located off the east coast of Japan.
This second leading edge of rain will arrive around midday Saturday. Moderate to heavy rain will then gradually shift south over the next two days, with heavy rain reaching the central Oregon Coast by early Sunday morning.
Aggressive rainfall estimates bring rain totals through Sunday evening to near 10 inches for the southwest slopes of the South Washington Cascades with areas near Mount Hebo in the Oregon Coast Range seeing around 8 inches.
In all, areas along the far North Oregon and South Washington coast will see 5 to 6 inches with amounts tapering off to the southeast, where the central Cascades are expected to receive around 1.30 inches.
In addition, windy conditions are expected to arrive along the coast Saturday. Wind gusts to at least 55 mph are possible along the coastal headlands and beaches, and to 45 mph or higher in the coastal communities and the higher elevations of the Coast Range.
Winds inland Saturday night could gust to 35 or 40 mph. Saturated soils and gusty winds and summer weakened trees will likely lead to another round of tree damage and power outages in many areas. Heavy rain could also lead to localized flooding, especially where drains and culverts are clogged. Smaller creeks and streams will likely run very high and may overflow their banks.