Flash flood warning issued for San Antonio as rain continues. Here's what we know.

Update: 9 a.m.
The Nation Weather Service issued a flash flood warning for parts of San Antonio including Kirby, Alamo Heights and Windcrest until noon.

Flash flood warnings mean that flash flooding is either happening or imminent in the warned area.

An offshore system of low atmospheric pressure has already produced anywhere from a half-inch to 1.5 inches of rain across Bexar County as of 9:30 a.m.

Gauges monitored by the Texas Water Development Board on its TexMesonet online dashboard showed that in the past 24 hours some of the heaviest rainfall, between 3 and 4 inches, was recorded in the Hill Country northwest of San Antonio and in areas along the Rio Grande southwest of the city.

In northwest Bexar County, as much as 1.6 inches of rain was measured near Texas 16 and Huebner Road, and about 1.7 inches was recorded at Olmos Creek and Dresden Road just north of San Antonio.

Meanwhile, the National Weather Service on early Tuesday issued a flood watch for the Rio Grande Plains, the southern Edwards Plateau, and portions of the western Hill Country through midnight. Forecasters cautioned that those areas could get another 2 to 4 inches later Tuesday.

Original story continues:

Tuesday could bring the best chances for rain in San Antonio this week, but don’t expect impressive rainfall amounts in South Texas.

The city has a 70% chance of showers, mainly after 1 p.m., but new rainfall amounts will be less than a tenth of an inch, National Weather Service forecasters said.

Morning temperatures Tuesday will begin in the upper 70s before peaking at 85 degrees in the afternoon around 5 p.m. under partly sunny skies, according to the weather service. Northeast winds of 10 mph could include gusts as strong as 20 mph.

Meanwhile, forecasters were anticipating the arrival of a broad area of low atmospheric pressure from off the Texas Gulf Coast. It was set to move inland over South Texas, bringing increased levels of moisture.

“The rain chances continue into Tuesday with at least scattered coverage of showers and storms developing into the afternoon, possibly numerous across the Hill Country, southern Edwards Plateau and Rio Grande,” the weather service said in a forecast bulletin Monday, adding that “the moisture content of the atmosphere will remain anomalously high” for this time of year.

But forecasters cautioned that the more favored areas for heavy rainfall would be the Hill Country, southern Edwards Plateau and the Rio Grande. Wherever the rain ends up, below-normal high temperatures are expected Tuesday because of the increased cloudiness.

Wednesday has a 40% chance of showers and thunderstorms under partly sunny skies. Temperatures will peak at 88 degrees amid northeast winds of 10 mph, including gusts as strong as 20 mph.

Meanwhile, a weak cold front will be making its way across Texas on Wednesday. The front could spread farther south and bring drier and more
stable air into the Hill Country and Central Texas, the weather service said. But forecasters remained wary of its chances of progressing.

“In early September, we should always be prepared for that cold front that never fully materializes, and this pattern isn’t strong enough to put those uncertainties to rest,” the weather service said in its forecast bulletin. “Temperatures will most likely be warmer once the front or fronts clear out the deep moisture, so the mildest daytime temperatures will be more associated with the cloud cover through Wednesday.”

Rain chances diminish even further on Thursday to just 30%, and peak temperatures inch closer to 90 degrees. By Friday, mostly sunny skies will help propel maximum temperatures to 91 degrees.

“By Saturday, the winds will start to shift to the south again as high pressure aloft strengthens back over Texas,” the weather service said. “Thus
next weekend will remind us that it’s still summer.”