Bay Area Downpours, Thunderstorms Possible In Hurricane Hilary's Wake

SAN FRANCISCO — Forecasters see a growing chance for rain showers and even potential downpours and thunderstorms in the Bay Area next week as tropical moisture unfurls in the wake of Hurricane Hilary.

The National Hurricane Center upgraded the storm to a category 2 hurricane Thursday morning, and forecasters expected it would become a major hurricane before the end of the day. The storm is expected to approach SoCal near tropical storm strength by late in the weekend. Depending on the final storm track, Hilary's remnants could still bring plenty of wet weather to NorCal, too.

With a few days to go, there are plenty of uncertainties in the forecast, and the storm's path will play an outsized role in how much rain will materialize across the Bay Area.

"Regardless of classification, copious tropical moisture will be drawn into the Desert Southwest and portions of California through early to midweek," NWS Bay Area forecasters wrote Thursday. "Shower and possible thunderstorm development will occur across parts of the region as well. There remains considerable uncertainty in local impacts as they are highly dependent upon Hilary's track."

The National Weather Service outlined three possible scenarios for the Bay Area, based on the latest information Thursday:

1. The ridge is weaker than anticipated and Hilary tracks more to the east. This scenario would displace the best moisture and greatest rain chances away from us. Mostly dry conditions might even prevail locally. This scenario is favored by some GEFS members, the EPS mean, along with the deterministic GFS and Global Canadian models.

2. The ridge is stronger causing Hilary to track more west. This scenario would bring deep tropical moisture into portions of our area leading to widespread showers and locally heavy rainfall. This
scenario is favored by several EPS members, a few GEFS members, and
the deterministic UKMET.

3. A hybrid of the above, with the best moisture displaced to our east but at least some chance for shower and isolated thunderstorm development.

Of note, forecasters said the National Blend of Models showed a 10 to 20 percent chance for at least 1 inch of rain next week, with the highest potential for communities southeast of the Golden Gate Bridge and in the inland Central Coast.

"Based on the possibility for at least localized flooding, a marginal risk for excessive rainfall was introduced by the Weather Prediction Center for our area on Monday," forecasters wrote. "There is a low confidence forecast, however, so keep up with the changes."

In a briefing shared Wednesday, NWS Bay Area showed a 15 to 30 percent chance for rain showers and locally heavy rain developing for the Peninsula, East Bay and South Bay, with lighter showers possible in the North Bay.

Forecasters expect temperatures will run considerably cooler by Monday amid widespread cloud cover. For now, the Bay Area can expect a pleasant weekend, with plenty of sunshine in the forecast and more seasonal temperatures.