The National Weather Service (NWS) is warning that heavy rainfall and flash flooding will become more likely over parts of the Southwest.

Saturday night: Showers and possibly a thunderstorm. Low around 60. East wind 5 to 15 mph, with gusts as high as 25 mph. Chance of precipitation is 90%. New rainfall amounts between a half and three quarters of an inch possible. 

Sunday: Showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 67. Windy, with an east wind 20 to 30 mph decreasing to 5 to 15 mph. Winds could gust as high as 55 mph. Chance of precipitation is 100%. New rainfall amounts between 2 and 3 inches possible. 

Sunday night: Showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Low around 60. Southwest wind 15 to 20 mph becoming south 10 to 15 mph after midnight. Winds could gust as high as 30 mph. Chance of precipitation is 100%. New rainfall amounts between 1 and 2 inches possible..

As Hillary continues to track north in the eastern Pacific near Baja California, the threat for heavy rainfall and flash flooding is likely to increase on Saturday, especially for portions of Southern California, western Arizona, and southern Nevada.

Riverside County is expecting widespread heavy rainfall, with as much as 10 inches of rain in some mountain and desert areas. It advises, prepare now. Sandbags are available at fire stations (Pine Cove, Garner Valley and Pinyon). Charge your phones. Keep fuel tanks and batteries full on your cars. Avoid waterways.

Mountain Disaster Preparedness President Mike Feyer said, "[W]e are ready to help … EMD in Riverside has asked us to be their eyes and ears here with our radio network (17 operators ready to observe and report). CERT has been notified to be ready if needed. That's what we are ready for along with potentially opening two of our DAS units for charging devices if power is out for an extended time. Very concerned that the town was full of visitors this AM. Hope they are smart and go home by this evening."

Hurricane Hillary is expected to impact Riverside County through the weekend. County departments have been working with local, state, and federal partners to prepare and are ready to mobilize quickly if needed.

“Hurricane Hillary will be here this weekend and we are asking everyone to prepare,” says Supervisor V. Manuel Perez, “The County is doing all we can to be ready and provide all the resources needed to our residents. If you don’t need to leave your house, don’t. Let’s stay safe everyone!”

“The County is coordinating with local, state, federal, tribal, and nonprofit agencies to make sure that we are ready for whatever this storm may bring. It is incredibly important that our residents take their own actions to ensure they are prepared as well. Plan now by having an emergency kit, ensuring that your gas tank is at least half full and that you keep your cell phones fully charged. All residents should sign up for Alert RivCo RivCoReady.org/AlertRivCo and follow all instructions from public safety agencies” said Bruce Barton, Riverside County Emergency Management Director.

This is the second time in history that a storm of this category makes landfall Southern California, the last time was 1939. Let’s stay #RivCoReady.

San Bernardino National Forest officials are cautioning the public that an incoming storm system could bring hazardous conditions over much of Southern California, including all three ranger districts of the forest, beginning this weekend through Tuesday. Rainfall is expected to be heaviest on the San Jacinto and Mountain Top ranger districts. Visitors planning to picnic, hike, hunt or camp over the next five days are strongly encouraged to monitor weather forecasts and potentially delay their visit until after Hurricane Hilary has passed through the area.

The following services will be closed to the public Sunday and Monday: the San Jacinto Ranger District Visitor Center; the Big Bear Discovery Center at the Mountain Top Ranger District and; the Lytle Creek, Mill Creek and Barton Flats visitor centers in the Front Country Ranger District.

“We encourage visitors to pay close attention to weather predictions as this storm approaches the San Bernardino National Forest,” said Deputy Forest Supervisor Amy Reid. “Be prepared for deteriorating conditions, and if you choose to travel make sure someone is aware of your plans.”

NWS has issued flood and tropical storm watches for the counties of San Bernardino and Riverside. High winds and heavy rainfall are expected throughout the region. Hazardous conditions including flooding, rockslides, mudslides, as well as falling limbs are possible.

Flash flooding can occur in places even when it is sunny overhead, so know the weather forecast and monitor conditions in the local area. Prepare to leave before conditions prevent a safe departure; depending on the location, it may be better to wait until the storm and flooding pass. For the next few days after the storm, stay off wet and muddy roads to prevent rutting and resource damage.

Visitors who have made reservations at concessionaire-managed campgrounds can inquire about a refund or future reservation through Recreation.gov.