Flood warnings are in place on Usk and Wye estuaries
People living in coastal areas are being warned to expect flooding, with high tides set to peak.
Six flood warnings are in place on Monday night, including areas around the Wye Estuary, the Usk Estuary and the tidal area at Crofty, Gower.
Ten flood alerts have also been issued, covering most of the Welsh coastline.
Natural Resources Wales (NRW) said astronomical tides would be "very high".
High tide at Newport is expected to reach 7.7m (25ft) at 20:55 BST.
NRW's Rick Park said with the relatively settled weather the risk of flooding to the majority of Wales was very low.