Thanks to a bit of high atmospheric pressure keeping South Texas skies cloud-free, San Antonio will kick off the work week Monday with plenty of sunshine and peak daily temperatures solidly in the 90s. Meanwhile, a persistent low-level flow of moisture-rich air from the Gulf of Mexico will add humidity to the summer-like heat this week.

“Feels like the start of summer,” the National Weather Service said in its forecast bulletin Sunday.

With so much moisture being brought in by balmy tropical winds, dew point temperatures will be rising and staying above 70 degrees for nearly the entire week, according to the weather service’s extended forecast.

Dew points, which are the temperatures when dew forms or when relative humidity reaches 100%, also can indicate the level of moisture in the air. Typically, the more saturated the air is with moisture, the higher the dew point. For instance, expect some oppressive, sticky air if the dew point is higher than 65 degrees.

San Antonio on Monday could see some clouds early in the day, courtesy of the humid air, before skies turn sunny by midday. Temperatures that afternoon will climb into the middle to upper 90s amid warm southerly winds of 5 to 10 mph.

But the moisture-rich air will drive up the heat index: While those air temperatures might be in the mid-90s, they’ll feel more like 100 degrees or more.

To understand what the heat index is, keep in mind that humidity, or the level of water vapor in the air, can make our perception of heat seem much hotter than the actual temperature. That’s because the body cools itself through the evaporation of sweat from our skin.

But evaporation isn’t as effective when there’s too much moisture already in the air. The heat index takes that into account, which is why the actual air temperature might be 95 degrees but a high humidity level (say, a dew point of 70 degrees) can make it feel like it’s 102 instead.

Tuesday and this week

Tuesday’s outlook for San Antonio includes partly sunny skies and, like the previous day, afternoon high temperatures near 96 degrees paired with gusty south-southeast winds of 10 mph. Another signal that summer-like heat has arrived: Nighttime and morning low temperatures are expected to stay above 75 most the week.

Meanwhile, the area of high pressure that kept Texas skies clear on Monday will start shifting east on Tuesday, which will open the door to more rain-friendly systems of low atmospheric pressure called shortwave troughs.

The weather service said “a shortwave trough slides through southern California and Arizona and eventually dampens east across Texas Thursday,” adding that “this will open the door for isolated to widely scattered showers and storms in the afternoons and evenings Wednesday through Friday along the Rio Grande and across the southern Edwards Plateau, Hill Country and Central Texas.”

But rain chances in this region, forecasters said, are currently only 10% to 30%, and even less for San Antonio.

In San Antonio on Wednesday and Thursday, we can expect partly sunny skies again with south-southeast winds and afternoon highs in the upper 90s.