Rhossili Bay • Statistics for December

December: Winter Swell Machine in Full Swing

December delivers the full winter treatment to Rhossili Bay. Average swell heights are back up to 1.5m (4.9ft) and average period hits 10.0s, while the distribution shows an impressive spread of powerful WSW groundswell: WSW accounts for 36.3% of all swell, W for 17.6%, and SW for 8.2%, with a solid portion of wave heights reaching 2-2.5m (6.6-8.2ft) and beyond. This is the kind of long-period, open-ocean swell that Rhossili's SSW-facing sandbars were made to handle. The wind remains the deciding factor: WSW is the most common wind direction at 9.6%, with onshore S/SSW/SW/WSW flow pushing 31%, while ideal offshore flow is limited to about 7%. Winter storms and frontal passages often bring strong onshore winds, but the intervals between fronts can deliver frozen, glassy N/NE mornings and world-class waves. Water temperatures drop to 10.2°C, air temperatures average 7.9°C, and rain totals climb to 4.41 mm/day. This is charging season, come prepared.