"We are asking you to evacuate those areas immediately, do not wait hoping the forecast will improve," Harris County Judge Lina Hidalgo said.
Forecasters predict the greatest threat will come from high wind speeds and a potential storm surge.
Zones A and B include Chambers and Brazoria counties and parts of eastern Harris County. The following ZIP codes are included:
Find a full list of ZIP codes here
Traffic flow and preparation
Those under voluntary evacuation orders should begin travel as soon as possible and if given the choice between traveling north or west, drive west to Katy or Cypress, for example, Hidalgo said.
Contraflow operations on highways will not be implemented, Hidalgo said. Mayor Sylvester Turner urged Houston residents who are not under an evacuation order to stay off the roads to clear the way for coastal residents. For those traveling through Houston, Turner recommended drivers plan to be off the roads by 8 p.m. Aug. 26 at the latest.
Those not asked to evacuate should stay in place and prepare for potentially prolonged power outages, Turner said.
Shelters will be open at the George R. Brown Convention Center, various Red Cross sites and hotels, if necessary. Shelters will be configured and supplied to promote social distancing and reduce the risk of coronavirus spread.