SAN DIEGO — San Diego is looking at a monsoonal-like weather pattern this week, bringing a chance of thunderstorms to parts of the region.

After a brief Mother’s Day warm-up, the National Weather Service forecasts a circular moisture aloft system will develop over neighboring states Monday, which will bring increased mid-level moisture to parts of San Diego County by mid-week.

This mid-level moisture could fire off isolated thunderstorms in mountain communities as early as Tuesday, NWS said. By Wednesday, this possible thunderstorm activity could move into desert areas.

Moving into the late part of the week, NWS forecasts a movement of moisture up from the Baja coast northward, which could drive possible thunderstorm activity into the west.

Chances for thunderstorm activity by Friday will remain highest in mountain areas, currently estimated by NWS as anywhere from 20 to 30%.

Along the coast, chances for thunderstorm activity range from 10 to 15%. Meanwhile, valley and desert communities see anywhere from a 15 to 20% likelihood.

Map showing the chance of thunderstorms in parts of Southern California on Friday, May 19. (Courtesy of National Weather Service San Diego)
Map showing the chance of thunderstorms in parts of Southern California on Friday, May 19. (Courtesy of National Weather Service San Diego)

“Most areas will be (missed) by these storms, but if you see lightning or hear (loud) thunder, head indoors,” NWS said in a tweet.

NWS outlooks for both temperatures and precipitation are forecasted to be likely above average for the week.

As of Sunday, no warnings have been put in place for hazardous conditions. However, strong rip currents and longshore currents are likely to be dangerous for swimming during the week.

According to NWS, monsoon weather patterns in Southern California traditionally occur in the summer months, from mid-July to September, transitioning into the Santa Ana Winds season.

These patterns are generally driven by high-pressure systems hanging over the southwest “Four Corners” states — Utah, Colorado, Arizona and New Mexico — that causes winds to rotate clockwise around, bringing muggy air or rain to Southern California.

This week’s weather patter, according to NWS, will mirror that development: the center of the circular system will be developing over the Four Corners area Monday, before slowly moving into a position over Nevada by the end of the week.

The reorientation will set Southern California up to see some of the monsoonal weather pattern.

The thunderstorm threat could start to lift early next week, according to NWS, if a drier flow aloft moves over the region. Should the aloft materialize, the threat of thunderstorm development will subside and bring a cooling trend for the week.