Storm parade and strong atmospheric river forecast for southern B.C., heavy rain into the weekend
A strong atmospheric river is forecast to shift southward along the British Columbia coast between September 26 and 29, 2025, bringing several low-pressure systems and periods of heavy rainfall to Vancouver Island and the South Coast. Forecasts suggest up to 100 mm (4 inches) of rain in west-facing coastal mountains, with persistent showers likely across the Lower Mainland.
Satellite image acquired at 23:40 UTC on September 24, 2025. Credit: NOAA/GOES-West, RAMMB/CIRA, The Watchers
A shift in the Pacific storm track is forecast to bring multiple low-pressure systems and an associated atmospheric river into southern British Columbia during the final weekend of September.
The storm track, which has delivered frequent precipitation to the Central and North Coast, is expected to shift south on September 26, focusing heavier rainfall over Vancouver Island and the South Coast.
Rainfall will begin on the North and Central Coast early Friday, September 26, before spreading southward through the day. By late Friday, precipitation will reach southern Vancouver Island and the Lower Mainland, with periods of steady rain continuing into September 27. Showers are expected to persist into September 28 and 29 as additional pulses of Pacific moisture move inland.
Forecasts suggest that west-facing slopes of Vancouver Island and the Coast Mountains may accumulate up to 100 mm (4 inches) of rainfall during the event. The Lower Mainland is forecast to see lower totals, though multiple rounds of showers are likely. Exact rainfall amounts remain uncertain, and totals may change as the system evolves.
At present, no official flood warnings or streamflow advisories have been issued, but residents are advised to monitor updates from Environment and Climate Change Canada and the B.C. River Forecast Centre for any changes.
September typically marks the transition into the wet season in British Columbia. Vancouver receives the majority of its annual rainfall between October and January, making this late-September atmospheric river an early signal of the seasonal increase in precipitation across the region.
At the same time, a plume of anomalously high monsoonal moisture streaming northward on the eastern flank of a slow-moving upper-level low will fuel several rounds of widespread showers and thunderstorms over the Desert Southwest into Sunday, September 28, with greatest impacts expected across southeastern Arizona and southwestern New Mexico.
Thunderstorms embedded within the moisture plume are expected to deliver high rainfall rates, raising the risk of flash flooding in vulnerable locations such as slot canyons, burn scars, and steep terrain. The NWS Tucson Forecast Office has issued a Flash Flood Watch for southeastern Arizona from September 26 through September 28.
The Weather Prediction Center has issued Excessive Rainfall Outlooks valid through September 29, with marginal risk (≥5%; level 1 of 4) extending over southern Arizona and New Mexico and slight risk (≥15%; level 2 of 4) focused along the Arizona–New Mexico border and southern New Mexico, highlighting the potential for flash flooding on multiple days.
I'm a dedicated researcher, journalist, and editor at The Watchers. With over 20 years of experience in the media industry, I specialize in hard science news, focusing on extreme weather, seismic and volcanic activity, space weather, and astronomy, including near-Earth objects and planetary defense strategies. You can reach me at teo /at/ watchers.news.
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