* WHAT. Heat index values up to 113. * WHERE. Zapata, Jim Hogg, Starr, Brooks, Hidalgo, Cameron, Willacy, and Kenedy County except the barrier islands. * WHEN. Until 8 PM CDT this evening. * IMPACTS. Heat related illnesses increase significantly during extreme heat and high humidity events. * ADDITIONAL DETAILS. Heat index values have reached 111 to 115 along and east of IH-69C and US 281 from Brooks and Hidalgo County to the west side of Laguna Madre. Values across the Brush Country, Rio Grande Plains, and upper Valley ranged from 105 to 109 at 3 pm and may not rise much more. but arrival of easterly winds between 4 and 5 PM may provide enough moisture to push values to 111 for two hours in these areas.