Highlights

Los Angeles, San Diego and over a dozen other California cities set all-time rainfall records for the month of July due to the unprecedented mid-summer rainfall, which one National Weather Service meteorologist called "super historic."

Part of Interstate 10 was washed out by flooding Sunday in the deserts of California .

Widespread showers and thunderstorms across the Desert Southwest have been fueled by moisture partially from former Hurricane Dolores.

Flash flood watches are in effect for parts of the West into Tuesday.

Dolores degenerated into a post-tropical low roughly 300 miles west of the coast of Baja California, Mexico, Saturday evening.

High surf and rip currents are likely along the west coast of Baja California early week, as well as the coast of southern California, due to swells generated when Dolores was a hurricane.

(MORE: State-by-State Southwest Storm Reports | Dolores Recap | Tropical Update )

Southwest Impacts

Dolores' path west of Baja California has sent a surge of deep tropical moisture up the Gulf of California into parts of the Desert Southwest.

This enhanced the threat of thunderstorms with heavy rainfall from the Four Corners into the Desert Southwest, including parts of New Mexico, Arizona, Utah, western Colorado, Nevada and the deserts and mountains of southern California.

(FORECAST: Phoenix | Tucson | Las Vegas )

More remarkably, the moisture has also reached the coastal cities of southern California, where July rainfall is rare and usually scant when it does happen.

That was not the case Saturday. San Diego broke its all-time July rainfall record Saturday when 1.03 inches fell. That broke not only the July single-day record of 0.83 inches set July 25, 1902, but also the record for an entire July's rainfall, which was 0.92 inches July 1-31, 1902.

It's also more rain than San Diego saw in all of January this year; on average, January is the second-wettest month and July the second-driest, with January averaging 66 times more rainfall than July. The only other time July has out-dampened January in San Diego was 1976, when July had 0.02 inch to January's trace.

San Diego added to its total Sunday with another 0.66 inch of rain as of 11 p.m. The month-to-date total of 1.70 inches, which fell in less than 36 hours, is more rainfall than San Diego had seen in the previous 101 Julys combined; a total of 1.68 inches fell during July from 1914 through 2014 in San Diego.

Los Angeles has also broken its July rainfall records. Downtown Los Angeles picked up 0.36 inch Saturday, which broke the July full-month record of 0.24 inch from July 1-31, 1886. Los Angeles International Airport saw 0.32 inch of rain, tying the record for all of July set in 1992.

LAX broke that record Sunday, adding another 0.03 inch. Downtown Los Angeles also had 0.02 inch Sunday by that time.

(FORECAST: Los Angeles | San Diego | Yosemite National Park )

Forecaster Joe Sirard of the National Weather Service told the Associated Press that with downtown Los Angeles in line for more rain, "It looks like there's a good chance the monthly record is going to go up. Really, this is super historic."

July is typically the driest month in Los Angeles with an average of 0.01 inch of rain for the whole month, so despite setting records, the rainfall will ultimately not put a huge dent in the ongoing drought.

Heavy rain was recorded on Saturday in Arizona as well. Northwest of Phoenix near Congress, Arizona 4.65 inches of rain fell in an hour and a half on Saturday evening and in Prescott 2.83 inches was measured.

The chance for rain will continue in parts of California and the Southwest early this week, especially in the mountains.

Though some drier air aloft has pushed into southern California, slow-moving thunderstorms may develop in the region late Monday, triggering significant local flash flooding, thanks to this moisture surge. Rainfall rates up to one inch per hour are possible in some of the thunderstorms. Mudslides and debris flows are also a risk with the heavy rain and a few thunderstorms may be strong to severe.

The core of the heaviest rains will be across eastern Arizona, southern Nevada and the high deserts and mountains of southern California. Flash flood watches have been issued for portions of this area into Tuesday.

Though Dolores is no longer a tropical cyclone, swells originated earlier in its existence will propagate northward to the beaches of Southern California into early this coming week. Surf is expected to build up to 6 feet and south-facing beaches will see the highest surf. Dangerous and frequent rip currents are also likely. If that weren't enough danger, lightning from passing thunderstorms will remain a concern.

MORE ON WEATHER.COM: Southwest Thunderstorms (PHOTOS)