When told to evacuate, it will be important to take the service animal with you. However, check with the local sheltering authority to see if service animals are allowed at evacuation facilities.
Many states designate shelters that allow animals. Other shelters may prohibit them. Shelters may require documentation that the animal is a service animal and that it has been vaccinated.
For more information, visit: http://www.extension.org/pages/Considerations_for_Evacuating_and_Sheltering.