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.

A Few Clouds

82°F

28°C

Humidity 77%
Wind Speed N 9 mph
Barometer 29.75 in (1006.8 mb)
Dewpoint 74°F (23°C)
Visibility 10.00 mi
Heat Index88°F (31°C)
Last update 17 Jun 9:56 am 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

  • Today

    Today: Mostly sunny, with a high near 91. Heat index values as high as 102. Calm wind becoming south southeast around 5 mph in the afternoon.

    High: 91 °F

    Mostly Sunny

  • Tonight

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

    Low: 77 °F

    Increasing
    Clouds

  • Thursday

    Thursday: Partly sunny, with a high near 96. Heat index values as high as 111. South wind 5 to 10 mph, with gusts as high as 20 mph.

    High: 96 °F

    Partly Sunny

  • 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: A 20 percent chance of showers and thunderstorms after 1pm. Partly sunny, with a high near 93. Southeast wind 5 to 10 mph.

    High: 93 °F

    Mostly Cloudy
    then Slight
    Chance
    T-storms

  • Friday Night

    Friday Night: A 30 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 77. South southeast wind 5 to 10 mph.

    Low: 77 °F

    Chance
    T-storms

  • Saturday

    Saturday: A 50 percent chance of showers and thunderstorms. Mostly cloudy, with a high near 91. South southeast wind 5 to 10 mph, with gusts as high as 20 mph.

    High: 91 °F

    Chance
    T-storms

  • Saturday Night

    Saturday Night: A 30 percent chance of showers and thunderstorms, mainly before 1am. Mostly cloudy, with a low around 77. South southeast wind around 10 mph.

    Low: 77 °F

    Chance
    T-storms

  • Sunday

    Sunday: Mostly sunny, with a high near 93. South wind 10 to 15 mph, with gusts as high as 25 mph.

    High: 93 °F

    Mostly Sunny

Detailed Forecast

Today
Mostly sunny, with a high near 91. Heat index values as high as 102. Calm wind becoming south southeast around 5 mph in the afternoon.
Tonight
Increasing clouds, with a low around 77. South southeast wind 5 to 10 mph.
Thursday
Partly sunny, with a high near 96. Heat index values as high as 111. South 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
A 20 percent chance of showers and thunderstorms after 1pm. Partly sunny, with a high near 93. Southeast wind 5 to 10 mph.
Friday Night
A 30 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 77. South southeast wind 5 to 10 mph.
Saturday
A 50 percent chance of showers and thunderstorms. Mostly cloudy, with a high near 91. South southeast wind 5 to 10 mph, with gusts as high as 20 mph.
Saturday Night
A 30 percent chance of showers and thunderstorms, mainly before 1am. Mostly cloudy, with a low around 77. South southeast wind around 10 mph.
Sunday
Mostly sunny, with a high near 93. South wind 10 to 15 mph, with gusts as high as 25 mph.
Sunday Night
Partly cloudy, with a low around 77.
Monday
Mostly sunny, with a high near 95.
Monday Night
Partly cloudy, with a low around 77.
Tuesday
Mostly sunny, with a high near 94.
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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:
8:44 am CDT Jun 17, 2026
Forecast Valid:
10am 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