Full moon high tide flood risk in Hobart

Low-lying parts of southern Tasmania are on flood watch with a full moon-high tide forecast to send water levels to an annual peak.

The Bureau of Meteorology has issued a severe weather warning for an abnormally high astronomical tide, expected to hit its high point at about 8.30am (AEDT) on Wednesday in and around Hobart.

"This high tide coincides with warmer than average water producing a positive sea level anomaly, and the passage of a deep low just south of Tasmania," the BoM website warns, adding that already high tides could be boosted by about 35cm.