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Full Breakdown

Atmospheric River Brings Flood Threat to California and the Southwest Over Halloween Weekend

By Drooid · · How we work

In this breakdown

01

Event Overview

A low-end “pineapple express” atmospheric river is expected to move from near Hawaii into the Desert Southwest and Southern California during the Halloween weekend. The system will deliver heavy rain on Saturday and peak early Sunday, with the potential for flash flooding in western Texas, the Phoenix metro area, the Four Corners region, and the foothills of San Diego County. Ground still saturated from 2–5 inches of rain last week heightens the risk of rapid runoff and debris flows, especially in recently burned areas.

The Weather ChannelBloomberg

02

Meteorological Background

The storm is being driven by a southward plunge of the jet stream off the West Coast, a pattern amplified by a strong El Niño winter. El Niño’s warm Pacific waters shift atmospheric circulation, steering moisture-laden storms toward the region. This “pineapple express” follows a similar path to previous El Niño-enhanced events that have produced record-setting rainfall in the Southwest.

Next storm set to soak California, Southwest in preview of wet Super El Niño winter pattern

Visual evidence

Images from the story

This is the forecast weather pattern for Halloween weekend, showing an atmospheric river headed into California and the Southwest
This is the forecast weather pattern for Halloween weekend, showing an atmospheric river headed into California and the SouthwestPhoto: weather
Both Northern and Southern California will face another storm system capable of heavy rain this Halloween weekend as a plume of tropical moisture from the remnants of Olana near Hawaii slams into the West Coast amid a rapidly strengthening El Niño climate pattern. This comes on the heels of storms that triggered flash flooding in parts of Southern California and deadly floods in the Four Corners region last week.
Both Northern and Southern California will face another storm system capable of heavy rain this Halloween weekend as a plume of tropical moisture from the remnants of Olana near Hawaii slams into the West Coast amid a rapidly strengthening El Niño climate pattern. This comes on the heels of storms that triggered flash flooding in parts of Southern California and deadly floods in the Four Corners region last week.Photo: foxweather
Floodwater from recent rains covers a roadway in Malibu, California, on October 22, 2026.
Floodwater from recent rains covers a roadway in Malibu, California, on October 22, 2026.Photo: foxweather

03

Forecast Details

The National Weather Service estimates atmospheric moisture over parts of Arizona, Colorado, Nevada and Utah could be two to three times the October average, approaching record levels for the season. The Weather Prediction Center assigns a 15 % chance of excessive rainfall in central Arizona and a 5 % chance in Southern California from Saturday into Sunday. Coastal flood warnings note tides will run nearly two feet (61 cm) above normal around San Diego and Los Angeles, a rise aided by the full moon and Kelvin waves.

BloombergThe Weather Channel

04

Official Warnings & Responses

Coastal flood advisories remain in effect through Friday, and flood watches cover central Arizona, including Phoenix. The National Weather Service urges parents to have backup plans for Halloween trick-or-treat activities. Jennifer Tate, a meteorologist at the U.S. Weather Prediction Center, emphasized that while California may see some rain, the greatest concern lies farther east, where heavier precipitation is expected.

Bloomberg

05

Verbatim Quotes

  • “California could get something, but it is really farther east of there that we are most concerned about,” — Jennifer Tate
Bloomberg