"An impactful storm system will bring rain and wind to the area today and tonight," the National Weather Service (NWS) Bay Area branch warned on X, the platform formerly known as Twitter.
The first of the two storms, heading from Hawaii to Northern California, could bring "quite rambunctious" winds from the Bay Area to the Central Coast, according to the local NWS.
Such winds, coupled with saturated soil conditions, could topple trees and cause power outages, the meteorologists warned on X.
"This one's going to pack quite a punch," Daniel Swain, a climate scientist at the University of California, Los Angeles, said in a Tuesday webinar.
Swain described the system as "a Pineapple Express-type atmospheric river," in which narrow regions of tropical moisture flow from Hawaii to the West Coast.
This first system will likely be strongest in the Monterey Bay area and northward, leading to "fairly widespread urban and small stream flooding," according to Swain.
As for Southern California, the NWS Los Angeles branch projected heavy rainfall and powerful winds for much of the region beginning on Wednesday afternoon.
While Swain acknowledged the "impressive" nature of the first storm, both he and the NWS expressed greater unease about the second system, set to arrive on Sunday.
Forecasters at the agency's Los Angeles branch discussed the second storm's potential "to spin down the coast and lift an atmospheric river" during its projected arrival.
The NWS predicted widespread rainfall of 2-4 inches for lower elevations and likely twice that amount for the south-facing mountains.
Higher elevations could endure "significant and hazardous snowfall" through Monday night, while lower altitudes could get some snow by late Tuesday, the forecast stated.
In terms of the accumulation of snowpack — mountain snow that melts in the spring to feed the region's rivers — the storms could be welcome news.
The water contained in statewide snowpack stood at only 8.4 inches, or 52 percent of the average for the date, California's Department of Water Resources announced Tuesday.
While this is a marked improvement from the 28 percent measured on Jan. 1, snowpack a year ago was 214 percent of the average on Feb. 1.
"This year's El Niño has delivered below average precipitation and an even smaller snowpack," Karla Nemeth, director of the Department of Water Resources, said in a statement.
El Niño typically brings warmer temperatures and more rainfall to Southern California but doesn't necessarily affect weather conditions in the North, according to the NWS.
As the Pineapple Express crossed the Pacific Tuesday, Swain warned that such rain and warmth combinations have not yielded "a good snow accumulation pattern for really anyone in the West yet."
Although he said that the second system, too, will be "a warm storm," Swain did identify "some cold air lurking just behind it" that could boost the potential for snowfall.
For now, however, Swain emphasized his concern about the second storm's potential to intensify as it hits on the coast — an unusual but not unprecedented phenomenon that can cause high-impact winds and major flood events.
"Southern California could actually get two to three times as much rain as Northern California," he said, noting a particular flood risk for the Tijuana River Watershed.
Deluges in this vulnerable region could exacerbate an existing pollution problem, in which raw sewage flows from the Mexican state of Baja California into its U.S. neighbor of similar name.
"Of course, this potential for very heavy rainfall early in the week does not stop at the international border," Swain said.
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