National Oceanic and Atmospheric Administration National Weather Service United States Department of Commerce

Excessive Rainfall and Tropical Storm in the South; Severe Thunderstorms in the Midwest

Excessive rainfall may produce considerable, potentially life-threatening, flooding across the lower Mississippi River Valley and central Great Lakes region through tonight. Tropical Storm Arthur will move northeastward along the Texas coast today and then move inland over southwestern Louisiana by tonight. An outbreak of severe thunderstorms is expected across portions of Illinois and Indiana. Read More >

Hazardous Weather Conditions

Current conditions at

San Marcos, San Marcos Municipal Airport (KHYI)

Lat: 29.89°NLon: 97.86°WElev: 597ft.

Mostly Cloudy

87°F

31°C

Humidity 70%
Wind Speed E 7 mph
Barometer 29.68 in (1004.4 mb)
Dewpoint 76°F (24°C)
Visibility 10.00 mi
Heat Index98°F (37°C)
Last update 17 Jun 1:56 pm CDT
Extended Forecast for

San Marcos TX

Extreme Heat Warning June 18, 12:00pm until June 18, 08:00pm
Click here for hazard details and duration
Extreme Heat Warning

  • This Afternoon

    This Afternoon: Sunny, with a high near 91. Heat index values as high as 101. East northeast wind around 5 mph becoming southeast.

    High: 91 °F

    Sunny

  • Tonight

    Tonight: Mostly clear, with a low around 77. South southeast wind 5 to 10 mph.

    Low: 77 °F

    Mostly Clear

  • Thursday

    Thursday: Mostly cloudy, then gradually becoming sunny, with a high near 95. Heat index values as high as 110. South southeast wind 5 to 10 mph, with gusts as high as 20 mph.

    High: 95 °F

    Decreasing
    Clouds

  • Thursday Night

    Thursday Night: Mostly cloudy, with a low around 79. South southeast wind 5 to 10 mph, with gusts as high as 20 mph.

    Low: 79 °F

    Mostly Cloudy

  • Juneteenth

    Juneteenth: Partly sunny, with a high near 92. Southeast wind 5 to 10 mph, with gusts as high as 20 mph.

    High: 92 °F

    Partly Sunny

  • Friday Night

    Friday Night: A chance of showers and thunderstorms before 1am, then a slight chance of showers between 1am and 4am, then a slight chance of showers and thunderstorms after 4am. Mostly cloudy, with a low around 78. South southeast wind 5 to 10 mph, with gusts as high as 20 mph. Chance of precipitation is 30%.

    Low: 78 °F

    Chance
    T-storms then
    Chance
    Showers

  • Saturday

    Saturday: A 50 percent chance of showers and thunderstorms, mainly after 1pm. Partly sunny, with a high near 91. South wind 5 to 10 mph, with gusts as high as 20 mph.

    High: 91 °F

    Slight Chance
    T-storms then
    Chance
    T-storms

  • Saturday Night

    Saturday Night: A slight chance of showers and thunderstorms. Mostly cloudy, with a low around 77. South southeast wind around 10 mph. Chance of precipitation is 20%.

    Low: 77 °F

    Slight Chance
    T-storms

  • Sunday

    Sunday: Partly sunny, with a high near 94. South wind 10 to 15 mph, with gusts as high as 25 mph.

    High: 94 °F

    Partly Sunny

Detailed Forecast

This Afternoon
Sunny, with a high near 91. Heat index values as high as 101. East northeast wind around 5 mph becoming southeast.
Tonight
Mostly clear, with a low around 77. South southeast wind 5 to 10 mph.
Thursday
Mostly cloudy, then gradually becoming sunny, with a high near 95. Heat index values as high as 110. South southeast wind 5 to 10 mph, with gusts as high as 20 mph.
Thursday Night
Mostly cloudy, with a low around 79. South southeast wind 5 to 10 mph, with gusts as high as 20 mph.
Juneteenth
Partly sunny, with a high near 92. Southeast wind 5 to 10 mph, with gusts as high as 20 mph.
Friday Night
A chance of showers and thunderstorms before 1am, then a slight chance of showers between 1am and 4am, then a slight chance of showers and thunderstorms after 4am. Mostly cloudy, with a low around 78. South southeast wind 5 to 10 mph, with gusts as high as 20 mph. Chance of precipitation is 30%.
Saturday
A 50 percent chance of showers and thunderstorms, mainly after 1pm. Partly sunny, with a high near 91. South wind 5 to 10 mph, with gusts as high as 20 mph.
Saturday Night
A slight chance of showers and thunderstorms. Mostly cloudy, with a low around 77. South southeast wind around 10 mph. Chance of precipitation is 20%.
Sunday
Partly sunny, with a high near 94. South wind 10 to 15 mph, with gusts as high as 25 mph.
Sunday Night
Mostly clear, with a low around 77.
Monday
Mostly sunny, with a high near 96.
Monday Night
Mostly clear, with a low around 77.
Tuesday
Partly sunny, with a high near 94.
Basemap Options
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Forecast Area
Tiles ©ESRI

ABOUT THIS FORECAST

 
Point Forecast:
San Marcos TX
 29.88°N 97.94°W (Elev. 577 ft)
Last Update:
1:24 pm CDT Jun 17, 2026
Forecast Valid:
2pm CDT Jun 17, 2026-6pm CDT Jun 23, 2026
 
Forecast Discussion
 
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Additional Resources

Radar & Satellite Image

Link to Local Radar Data Link to Satellite Data

Hourly Weather Forecast

National Digital Forecast Database

National Digital Forecast Database Maximum Temperature Forecast

High Temperature

National Digital Forecast Database Weather Element Forecast

Chance of Precipitation