Forecast models from the National Weather Service and private sources converge on a daytime high near 100°F for Austin on September 13, driven by southerly flow, abundant low-level moisture, and mostly sunny skies that favor strong solar heating after a mild overnight low in the upper 70s. With dew points in the low-to-mid 70s, heat indices are projected to reach 105–107°F, consistent with late-summer climatology that routinely pushes Central Texas temperatures several degrees above the 91.6°F September 13 average. Recent model runs show little spread and no incoming frontal boundary or increased cloud cover that would cap afternoon readings, supporting the market’s heavy weighting toward the 98–101°F bins. Updated hourly guidance and any afternoon observation shifts remain the key near-term variables.