Galveston Mayor Pro Tem Craig Brown issued the order for the areas within the city limits, as county judge Mark Henry issued the order covering Bolivar.
"The reason for the voluntary evacuation is the peninsula has the chance of being cut off from the rest of the county," Henry said.
Ferry service between the island and Bolivar could be impacted and water could begin to rise over Highway 87 as water rises due to anticipated storm surge, Henry said.
According to the National Weather Service forecast issued Saturday morning, Beta was expected to create tides six feet above mean low tide beginning Sunday night and continuing through Thursday, as well as up to 10 inches of rainfall over several days. This tide level would create impassable roads, particularly along the west end and low-lying areas along the coast.
Henry did not anticipate a mandatory evacuation, but the county was staging high water vehicles in the event rescues are needed.
In Harris County, a voluntary evacuation was issued Saturday afternoon for Seabrook's low-lying areas that are prone to flooding.
As of Saturday morning Tropical Storm Beta had 60 mph max winds. Hurricane and storm surge watches have been issued for our entire coastline.
"The good news is, as it picks up speed, we expect it to be fully over with by Wednesday," Henry said.
WATCH: Galveston beach before Beta's impacts
Montgomery/Walker/San Jacinto/Polk/Grimes Counties
Fort Bend/Wharton/Colorado Counties
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