US: Tropical Storm Hilary tracking north-northwestward across Los Angeles County, California, as of late Aug. 20 /update 5

Event

Tropical Storm Hilary has weakened and is tracking north-northwestward across Los Angeles County, California, US late Aug. 20, following landfall over Baja California, Mexico earlier in the day. As of 20:00 PDT, the system's center of circulation was approximately 170 km (105 miles) northwest of San Diego, California.

Forecast models indicate that the storm will weaken into a tropical depression as it tracks generally northward across southern California, then western Nevada, US, through late Aug. 20 before dissipating over western Nevada early Aug. 21. Some uncertainty remains in the track and intensity forecast, and significant changes could occur over the coming hours.

As of late Aug. 20, authorities have issued the following coastal watches and warnings:

• Tropical Storm Warning: San Felipe to Puerto Penasco in Mexico, California/Mexico border to Point Mugu, and Catalina Island.

Authorities will likely issue new warnings or update existing advisories throughout the system's progression in the coming hours and days.

Rainfall totals of 7.5-15 cm (3-6 inches), with localized maximums of up to 25 cm (10 inches), are forecast across parts of the northern Baja California Peninsula through late Aug. 20. Flash and urban flooding, locally catastrophic, is likely. Similar rainfall amounts are forecast in parts of southern California and southern Nevada; dangerous to catastrophic flooding is expected in these areas. Totals of 2.5-7.5 cm (1-3 inches) are forecast across portions of Oregon and Idaho through early Aug. 22. Localized, and in places significant, flash flooding is likely.

Storm surge could produce coastal flooding along the northern coast of the Gulf of California through early Aug. 21. Large swells generated by Hilary, which are likely to cause life-threatening surf and rip current conditions, are forecast across Baja California Peninsula and southern California through early Aug. 21. Tornadoes associated with the storm system are possible across southeast California, northwest Arizona, southern Nevada, and far southwest Utah the evening of Aug. 20.

Authorities opened 113 emergency shelters in Baja California Sur State and 80 in Baja California State ahead of the approach of the storm. Authorities have evacuated around 90 people from at-risk areas between Puerto Alcatraz and Cancun in Baja California Sur. As of Aug. 20, more than 110 people are sheltering in temporary shelters in Isla de Cedros and the municipality of San Felipe. The governor of Baja California State has advised citizens to shelter in place during the passage of the storm, and nonessential public activities have been canceled throughout the state through Aug. 21. Authorities have reported one fatality in Mulege Municipality, Baja California Sur State Aug. 19 and another fatality in Culiacan City, Sinaloa State, Aug. 17 due to floodwaters. Several roads have been made impassable by flooding and landslides in the state, including parts of the Federal Highway 1 connecting Tijuana with Cabo San Lucas, and at least 21 flights have been canceled at Los Cabos International Airport (SJD). One fatality was also reported in the El Quemadito community in Sinaloa State due to flooding following heavy rainfall associated with the passing of Hilary.

California declared a state of emergency across southern parts of the state Aug. 19, while Nevada declared a state of emergency Aug. 20. San Bernardino County and San Diego City, California, also declared states of emergency Aug. 20. Authorities issued the following evacuation orders and warnings:

• Evacuation orders: Mias Canyon of the Apple/El Dorado fires burn scar in Riverside County and the communities of Oak Glen, Forest Falls, Mountain Home Village, Angelus Oaks, and northeast Yucaipa in San Bernardino County in California. The Temple Bar and Willow Beach areas of Lake Mead National Park in Arizona are also under evacuation orders.

• Evacuation warnings: Silverado and Williams canyons in Orange County, Fairview and the rest of Apple/El Dorado fires burn scars, Banning Bench, Reche Canyon, Snow Creek, and Bonny in Riverside County, and Bobcat and Lake fire burn scars and Catalina Island in Los Angeles County.

The Red Cross has established emergency shelters in Imperial, Orange, Riverside, San Bernardino, and San Diego counties. Additional evacuations are possible as the storm approaches and weather conditions deteriorate.

Southwest Airlines (WN) has canceled all flights at Palm Springs International Airport (PSP) through early Aug. 21 and at Ontario International Airport (ONT) through late Aug. 21. Frontier Airlines (F9) has canceled all flights at Ontario International Airport (ONT) Aug. 20-21. Thousands of flights across southern California, including flights at San Diego International (SAN), Los Angeles International (LAX), Hollywood Burbank (BUR), and John Wayne (SNA) airports, have been canceled Aug. 20-21. Hundreds of flights at Harry Reid International Airport (LAS) and Phoenix Sky Harbor International Airport (PHX) were also canceled Aug. 20. Officials have canceled several sports events in parts of southern California over the weekend due to the anticipated severe weather brought by the storm. Authorities have closed parks, beaches, and other facilities across southern California, including Joshua Tree National Park, Mojave National Preserve, Death Valley National Park, and all San Diego and Orange counties state beaches, through at least Aug. 22 in advance of the storm. As of late Aug. 20, more than 66,000 people across California are without power. Los Angeles and San Diego counties closed all schools Aug. 21.

Sustained heavy rainfall could trigger flooding in low-lying areas and those with easily overwhelmed drainage systems. If weather conditions prove hazardous, localized evacuations, flash flooding, and landslides are possible.

The inclement weather could trigger localized business, transport, and utility disruptions and render some bridges or roadways impassable. Flight disruptions at regional airports and temporary closures of ports are also possible. Stagnant pools of water during and after flooding increase insect- and waterborne diseases, such as dengue fever, cholera, and malaria. Exposure to raw sewage and other hazardous materials mixed with floodwaters poses a serious health threat.

Advice

Activate contingency plans in areas where officials forecast tropical storm conditions. Heed any evacuation orders that may be issued. Use extreme caution in low-lying coastal areas and near streams, creeks, and other waterways due to the potential for severe flooding and storm surge. Stockpile water, batteries, and other essentials in advance. Charge battery-powered devices when electricity is available; restrict the use of cellular phones to emergencies only. Power down mobile devices when not in use. Keep important documents and necessary medications in waterproof containers. Observe strict food and water precautions, as municipalities could issue boil-water advisories following flooding events. Take precautions against insect- and waterborne diseases in the coming weeks.

Plan accordingly for protracted commercial, transport, and logistics disruptions in areas in the path of the storm, especially if vital infrastructure is damaged. Seek updated information on road conditions before driving or routing shipments through areas where flooding has occurred. Confirm flights before checking out of hotels or driving to the airport; clearing passenger backlogs may take several days in some locations.

Resources

US National Hurricane Center
Mexico National Meteorological Service (SMN)