Sea temperature by month at UK and European ferry ports

The average sea temperature for every month at the 84 ferry ports I list that have climate data, from Shetland to the Canary Islands and Greece, with the average daily high and low on land beside it. Pick a port to see its ferries.

What the numbers show

In August the warmest sea at a port I list is at Palma (Balearic Islands): 28.3°C (Open-Meteo Marine, 2023–2024 average).
In February the coldest sea is at Harwich (England) and Heysham (England): 6.4°C (Open-Meteo Marine, 2023–2024 average).
At the 45 UK ports with sea data, the August sea runs from 13.1°C at Lerwick to 20.4°C at Harwich (Open-Meteo Marine, 2023–2024 average).
29 of the 82 ports with sea data average 20°C or more in August (Open-Meteo Marine, 2023–2024 average).
On land, the highest average daily high in August is 34.0°C, at Piraeus (Greece): ERA5 via Open-Meteo, 1991–2020 average.

Temperature by month at each port

Sea: 2023–2024 monthly averages. Air: 1991–2020 averages of the daily high and low. Switch tables with the buttons; each table scrolls sideways on a phone.

SeaAir: daily highAir: daily low

Average sea surface temperature, °C (2023–2024, Open-Meteo Marine)
Port	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
France
Caen	8.4	8.5	9.1	11.0	14.4	17.2	19.3	20.4	19.1	16.6	13.0	10.0
Calais	8.8	8.4	8.8	10.3	13.2	15.9	18.6	19.7	19.1	16.5	13.4	10.5
Cherbourg	10.1	9.7	9.4	10.6	12.7	15.2	17.2	18.3	18.0	16.5	14.2	11.8
Dieppe	8.2	8.4	8.9	10.7	14.1	17.4	19.3	20.4	19.0	16.4	12.9	9.8
Dunkirk	8.0	8.0	8.6	10.6	13.8	16.8	18.9	20.0	19.2	16.1	12.5	9.4
Roscoff	11.2	10.8	10.9	11.8	13.8	16.2	17.5	18.6	17.5	16.0	14.3	12.7
St Malo	9.2	9.0	9.5	11.4	14.3	17.7	19.3	20.0	19.3	17.0	13.5	10.6
Spain
Algeciras	16.9	16.3	15.9	16.8	17.4	19.2	20.3	22.3	22.0	19.4	18.4	17.7
Barcelona	14.0	13.5	14.3	15.6	18.4	21.8	25.5	27.4	25.2	22.2	17.8	15.6
Bilbao	13.9	13.3	13.4	14.4	16.5	19.8	21.9	22.8	21.5	19.4	17.2	14.7
Santander	14.4	13.8	13.6	14.3	16.0	19.2	21.6	22.5	21.3	19.2	16.9	15.0
Ireland
Cork	9.1	9.3	9.2	10.3	13.2	14.9	14.0	13.8	15.9	13.8	12.3	10.4
Dublin	7.2	7.6	7.9	10.2	13.8	16.2	16.1	16.9	16.2	14.0	11.5	8.4
Rosslare	8.8	8.6	8.7	10.1	12.6	14.6	14.3	14.7	16.1	14.0	12.5	10.4
Netherlands
Amsterdam	6.4	6.8	7.6	9.7	13.4	16.9	19.1	20.0	19.3	15.6	11.6	8.0
Hook of Holland	6.5	6.9	7.8	10.1	13.9	17.5	19.2	20.1	19.4	15.6	11.5	8.0
Rotterdam	6.3	6.8	7.8	10.2	14.2	17.9	19.4	20.3	19.4	15.5	11.2	7.7
Isle of Wight
Cowes	9.0	8.6	8.7	10.5	13.2	15.8	16.3	17.6	18.2	16.5	13.5	10.7
East Cowes	9.0	8.6	8.7	10.5	13.2	15.8	16.3	17.6	18.2	16.5	13.5	10.7
Fishbourne	9.0	8.6	8.7	10.4	13.2	15.7	16.2	17.5	18.2	16.5	13.5	10.7
Ryde	9.0	8.6	8.7	10.4	13.2	15.7	16.0	17.4	18.2	16.5	13.6	10.8
Yarmouth	8.4	8.3	8.7	10.7	13.8	17.0	18.5	19.4	18.7	16.2	12.9	10.1
Scotland
Aberdeen	7.3	6.5	6.5	7.6	10.7	13.2	14.1	14.9	14.0	12.2	10.6	8.7
Ardrossan	8.9	8.4	8.8	9.8	12.2	13.6	14.3	15.0	15.1	13.8	12.4	10.7
Armadale	9.0	8.1	7.9	8.7	11.4	13.9	14.1	14.4	14.2	12.9	11.8	10.3
Brodick	9.0	8.3	8.7	9.6	12.3	13.3	14.0	14.8	15.1	13.8	12.6	10.8
Cairnryan	8.4	8.5	8.4	9.7	12.4	14.2	15.1	16.0	15.6	13.8	11.9	9.9
Castlebay	9.1	8.7	8.3	9.0	11.2	13.4	14.0	14.5	14.3	12.9	11.7	10.4
Craignure	8.9	8.2	7.9	8.8	11.7	13.9	14.3	14.5	14.5	12.9	11.9	10.5
Cumbrae	8.9	8.3	8.6	9.7	12.1	13.4	14.1	14.9	14.9	13.6	12.3	10.7
Gills Bay	8.6	7.9	7.6	8.1	10.0	11.8	13.5	13.8	13.6	12.3	11.0	9.7
Kirkwall	8.4	7.8	7.4	8.0	9.7	11.5	12.6	13.3	13.4	12.3	10.9	9.5
Largs	8.9	8.3	8.6	9.7	12.1	13.4	14.1	14.9	14.9	13.6	12.3	10.7
Lerwick	7.8	7.4	7.3	7.9	9.4	11.6	13.3	13.1	12.8	11.5	10.0	8.8
Lochmaddy	8.0	7.7	7.6	8.9	11.7	13.5	13.9	14.0	13.9	12.2	10.7	9.3
Mallaig	8.8	8.0	7.8	8.6	11.5	14.0	14.2	14.4	14.0	12.7	11.6	10.1
Oban	7.8	7.5	7.7	8.5	11.3	13.8	14.1	14.2	14.1	12.3	10.9	9.4
Rothesay	8.8	8.1	8.3	9.4	11.9	13.1	13.8	14.7	14.9	13.6	12.2	10.6
Scrabster	8.7	8.0	7.7	8.2	10.1	12.1	13.5	13.9	13.6	12.4	11.1	9.7
St Margaret's Hope	8.5	7.9	7.5	8.0	9.7	11.5	12.9	13.4	13.4	12.3	10.9	9.6
Stornoway	9.3	8.4	8.0	8.6	10.6	12.2	13.4	13.9	13.5	12.5	11.5	10.3
Stromness	8.7	8.0	7.6	8.1	9.8	11.6	12.8	13.4	13.4	12.3	11.0	9.7
Tarbert	9.6	8.5	8.2	8.6	10.8	12.1	13.1	13.7	13.9	13.2	12.0	10.8
Uig	9.2	8.3	8.1	8.5	11.1	12.8	13.5	13.9	13.9	12.9	11.8	10.6
Channel Islands
Guernsey	10.7	9.9	9.7	10.6	12.8	15.5	16.6	17.6	17.8	16.9	14.6	12.4
Jersey	9.4	9.1	9.2	11.0	14.1	16.9	18.0	19.0	18.9	16.7	13.7	11.2
Isle of Man
Douglas	9.4	8.2	8.3	9.4	11.8	14.3	14.8	15.9	16.0	14.4	12.6	10.6
Isles of Scilly
St Mary's	10.8	10.6	10.5	11.0	13.1	14.9	16.0	16.5	16.0	14.5	13.2	11.9
England
Dover	8.8	8.5	8.6	10.1	12.6	15.4	17.0	18.6	18.5	16.7	13.8	10.9
Harwich	5.7	6.4	7.5	10.6	14.3	17.6	19.4	20.4	19.4	14.9	10.6	7.3
Heysham	5.6	6.4	7.1	10.0	14.2	17.2	17.5	18.0	16.7	13.1	10.0	7.2
Hull	–	–	–	–	–	–	–	–	–	–	–	–
Liverpool	5.6	6.5	7.3	10.2	14.4	17.7	17.9	18.4	16.8	13.1	9.9	7.2
Lymington	8.9	8.5	8.7	10.6	13.5	16.4	17.1	18.2	18.4	16.2	13.3	10.5
Newcastle	6.8	6.7	6.9	8.2	11.8	14.4	14.7	15.3	14.7	11.8	10.1	8.3
Newhaven	8.5	8.4	8.6	10.5	13.4	16.2	17.9	19.1	18.5	16.2	13.2	10.2
Penzance	10.1	9.8	9.8	10.9	12.9	14.5	13.7	14.6	16.1	14.3	13.0	11.5
Plymouth	9.8	9.8	9.8	11.0	13.5	15.7	15.6	16.8	17.3	15.7	13.5	11.5
Poole	9.4	9.0	9.0	10.5	13.0	15.5	15.4	16.5	17.8	16.4	13.8	11.1
Portsmouth	8.1	8.1	8.5	10.7	14.2	17.2	17.8	19.0	18.8	16.0	12.7	9.8
Southampton	8.4	8.3	8.7	10.7	13.8	17.0	18.5	19.4	18.7	16.2	12.9	10.1
Southsea	8.1	8.1	8.5	10.7	14.2	17.2	17.8	19.0	18.8	16.0	12.7	9.8
Wales
Fishguard	9.9	9.2	8.9	10.1	12.6	15.1	16.1	16.9	16.8	14.8	13.3	10.9
Holyhead	8.9	8.6	8.5	9.8	12.4	14.8	16.0	16.7	16.3	14.6	12.8	10.7
Pembroke	9.4	8.9	8.7	10.2	12.9	15.4	16.0	17.1	17.1	15.4	13.6	11.4
Northern Ireland
Belfast	–	–	–	–	–	–	–	–	–	–	–	–
Larne	9.4	8.9	8.8	9.5	11.6	13.7	14.6	15.2	15.3	14.0	12.8	11.0
Balearic Islands
Ibiza	15.9	15.0	15.2	16.9	19.8	23.3	26.8	27.7	26.2	23.4	20.0	17.5
Palma	15.2	14.7	15.2	16.9	19.8	23.3	26.9	28.3	26.3	23.6	19.8	16.9
Canary Islands
Corralejo	20.3	19.3	19.3	19.6	20.6	22.0	22.6	23.1	23.0	23.2	22.4	21.3
Los Cristianos	21.2	20.4	20.6	20.9	21.5	22.7	23.5	24.0	24.3	24.4	23.6	22.4
Playa Blanca	20.4	19.3	19.4	19.7	20.5	21.9	22.6	23.2	23.1	23.3	22.6	21.4
San Sebastián	21.3	20.4	20.8	21.0	21.6	22.8	23.7	24.0	24.4	24.6	23.6	22.5
Italy
Capri	16.5	15.2	15.3	16.4	19.3	24.0	27.7	27.7	25.3	23.6	20.6	18.0
Casamicciola	16.5	15.2	15.2	16.4	19.3	23.9	27.3	27.6	25.3	23.4	20.7	18.0
Naples	16.4	15.0	15.0	16.3	19.2	23.9	27.3	27.5	25.5	23.4	20.6	18.0
Sorrento	16.5	15.1	15.2	16.4	19.4	23.9	27.4	27.5	25.4	23.4	20.8	18.0
Greece
Paros	16.6	16.4	16.7	17.5	18.7	22.5	24.4	25.6	24.8	23.2	20.5	18.6
Piraeus	16.8	15.8	15.7	17.3	19.1	23.7	27.0	27.8	26.0	24.3	21.9	17.9
Croatia
Dubrovnik	15.8	14.8	15.0	16.5	19.3	24.4	27.0	27.0	25.1	22.7	19.8	17.3
Hvar	15.3	14.6	14.9	16.2	18.9	23.6	26.0	26.4	24.9	22.6	19.7	16.7
Split	14.9	14.0	14.3	16.0	18.7	23.3	26.4	26.6	24.4	22.2	19.7	16.6
Supetar	15.1	14.3	14.4	16.1	18.7	23.5	26.6	26.7	24.5	22.3	19.8	16.7
Malta
Gozo	17.4	16.2	16.1	16.8	18.6	22.8	26.4	27.2	26.4	24.8	22.7	19.5

Average daily high air temperature, °C (1991–2020, ERA5 via Open-Meteo)
Port	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
France
Caen	8.3	9.1	11.9	14.8	17.9	21.0	23.1	23.2	20.3	16.2	11.7	8.8
Calais	7.3	7.7	10.2	13.2	16.2	18.9	21.1	21.4	18.8	15.0	10.7	7.9
Cherbourg	8.7	8.9	10.8	13.0	15.7	18.5	20.5	20.7	18.7	15.5	11.9	9.5
Dieppe	7.6	7.9	10.2	12.8	15.6	18.4	20.5	21.0	18.8	15.3	11.1	8.3
Dunkirk	7.1	7.6	10.2	13.4	16.5	19.2	21.6	21.8	19.0	15.0	10.6	7.7
Roscoff	9.7	10.1	12.0	14.0	16.8	19.3	21.2	21.3	19.5	16.1	12.5	10.3
St Malo	9.1	9.8	12.2	14.6	17.5	20.4	22.3	22.5	20.4	16.5	12.4	9.6
Spain
Algeciras	15.6	16.0	17.5	19.0	21.6	24.8	27.6	27.9	25.4	22.2	18.5	16.4
Barcelona	13.6	14.2	16.3	18.1	21.3	25.1	27.8	28.2	25.1	21.6	17.1	14.2
Bilbao	12.7	13.2	15.0	16.2	18.9	21.5	23.4	24.3	22.6	20.0	15.7	13.4
Santander	12.5	12.6	14.2	15.2	17.8	20.4	22.5	23.3	21.8	19.3	15.5	13.4
Ireland
Cork	9.1	8.9	9.6	10.9	13.1	15.7	17.3	17.5	16.2	13.8	11.2	9.7
Dublin	8.4	8.7	10.1	12.1	14.7	17.3	19.0	18.8	16.9	13.8	10.8	8.8
Rosslare	8.9	8.5	8.8	9.8	11.7	13.9	15.6	16.2	15.5	13.7	11.4	9.7
Netherlands
Amsterdam	5.8	6.0	8.4	11.8	15.0	17.6	19.9	20.2	17.6	13.8	9.7	6.7
Hook of Holland	6.0	6.4	9.1	12.7	16.0	18.6	20.8	21.0	18.2	14.2	9.9	6.8
Rotterdam	6.0	6.4	9.1	12.7	16.0	18.6	20.8	21.0	18.2	14.2	9.9	6.8
Isle of Wight
Cowes	8.4	8.4	10.3	12.9	16.1	18.9	21.0	20.8	18.6	15.0	11.5	9.1
East Cowes	8.3	8.3	10.3	12.9	16.0	18.8	20.9	20.8	18.5	14.9	11.4	9.0
Fishbourne	8.4	8.4	10.3	12.9	16.1	18.9	21.0	20.8	18.6	15.0	11.5	9.0
Ryde	8.5	8.4	10.4	13.0	16.1	18.9	21.0	20.9	18.6	15.0	11.5	9.1
Yarmouth	8.3	8.1	9.6	11.8	14.8	17.4	19.5	19.7	17.9	14.7	11.4	9.1
Scotland
Aberdeen	7.0	7.3	8.7	10.4	12.7	15.1	17.2	17.3	15.6	12.5	9.5	7.2
Ardrossan	7.7	8.0	9.3	11.7	14.6	16.7	18.1	18.1	16.2	13.1	10.1	7.9
Armadale	7.2	7.2	8.3	10.4	12.9	14.7	16.1	16.3	14.9	12.2	9.6	7.6
Brodick	7.6	7.1	7.6	9.0	11.3	13.3	14.9	15.3	14.2	12.2	9.9	8.2
Cairnryan	7.9	7.6	8.2	9.6	11.9	13.8	15.4	15.8	14.9	12.8	10.3	8.6
Castlebay	8.4	7.8	7.9	8.7	10.3	12.2	13.7	14.4	13.7	12.0	10.3	9.0
Craignure	7.6	7.5	8.5	10.3	12.8	14.6	16.0	16.2	15.0	12.5	9.9	8.0
Cumbrae	7.6	7.5	8.5	10.4	13.0	15.1	16.6	16.7	15.2	12.6	9.9	8.0
Gills Bay	7.2	7.1	7.9	9.2	11.1	13.2	15.2	15.5	14.3	11.9	9.5	7.6
Kirkwall	7.3	6.6	6.8	7.5	8.9	10.7	12.6	13.4	12.9	11.2	9.4	7.9
Largs	7.7	8.0	9.3	11.7	14.6	16.7	18.1	18.1	16.2	13.1	10.1	8.0
Lerwick	7.1	6.5	6.6	7.2	8.5	10.4	12.2	13.1	12.2	10.6	8.9	7.7
Lochmaddy	8.1	7.6	7.7	8.5	10.1	12.0	13.6	14.2	13.5	11.8	10.1	8.8
Mallaig	7.2	7.2	8.3	10.4	12.9	14.7	16.1	16.3	14.9	12.2	9.6	7.6
Oban	7.4	7.5	8.8	11.0	13.7	15.6	17.0	17.0	15.5	12.6	9.8	7.6
Rothesay	7.6	7.6	8.5	10.4	13.0	15.1	16.6	16.8	15.3	12.7	10.0	8.1
Scrabster	7.5	7.7	8.9	10.7	12.8	14.9	17.0	17.1	15.5	12.6	9.8	7.7
St Margaret's Hope	7.2	6.6	6.8	7.7	9.1	11.1	12.9	13.6	13.0	11.3	9.4	7.8
Stornoway	8.1	8.3	9.3	11.3	13.6	15.5	17.2	17.2	15.5	12.7	10.1	8.3
Stromness	7.2	6.6	6.8	7.6	9.0	10.8	12.7	13.5	12.9	11.2	9.4	7.9
Tarbert	8.1	8.2	9.1	10.9	13.2	15.1	16.7	16.8	15.2	12.6	10.1	8.4
Uig	8.5	8.3	9.1	10.8	13.1	14.8	16.4	16.6	15.2	12.8	10.5	8.9
Channel Islands
Guernsey	9.8	9.2	9.6	10.6	12.5	14.6	16.5	17.4	17.0	15.3	12.8	10.8
Jersey	9.0	8.5	9.4	10.9	13.3	15.6	17.5	18.3	17.4	15.2	12.3	10.1
Isle of Man
Douglas	8.0	7.5	7.8	9.0	11.0	13.1	14.9	15.6	14.9	13.1	10.7	9.0
Isles of Scilly
St Mary's	10.3	9.7	9.8	10.6	12.4	14.8	16.7	17.2	16.2	14.4	12.4	11.1
England
Dover	7.6	7.6	9.6	12.1	15.1	18.0	20.4	20.8	18.2	14.7	10.9	8.3
Harwich	7.2	7.1	8.9	11.4	14.4	17.4	20.0	20.2	17.8	14.3	10.5	7.8
Heysham	7.2	7.5	9.1	11.7	14.7	17.0	18.7	18.5	16.6	13.4	10.0	7.7
Hull	7.0	7.5	9.3	11.5	14.2	17.1	19.5	19.6	17.3	13.7	9.9	7.3
Liverpool	7.4	7.5	8.9	11.1	14.0	16.4	18.2	18.3	16.6	13.5	10.3	8.0
Lymington	8.4	8.1	9.6	11.8	14.8	17.5	19.5	19.7	17.9	14.7	11.4	9.1
Newcastle	7.1	7.7	9.5	11.7	14.6	17.3	19.7	19.4	17.0	13.4	9.8	7.4
Newhaven	7.9	8.1	10.5	13.2	16.3	19.1	21.3	21.3	18.7	14.9	11.1	8.4
Penzance	9.8	9.3	9.7	10.8	12.9	15.3	17.1	17.5	16.4	14.2	12.0	10.6
Plymouth	8.9	9.0	10.7	13.0	15.8	18.3	20.0	19.9	18.0	14.8	11.6	9.5
Poole	8.4	8.4	10.2	12.6	15.6	18.3	20.4	20.3	18.3	14.8	11.4	9.1
Portsmouth	8.4	8.4	10.3	13.0	16.1	18.9	21.0	20.9	18.6	15.0	11.5	9.1
Southampton	8.1	8.4	10.7	13.5	16.6	19.4	21.5	21.2	18.7	14.9	11.1	8.6
Southsea	8.4	8.4	10.3	12.9	16.1	18.9	21.0	20.8	18.6	15.0	11.5	9.1
Wales
Fishguard	8.5	8.3	9.4	11.2	13.6	15.8	17.5	17.7	16.6	14.0	11.2	9.2
Holyhead	8.6	8.5	9.8	12.0	14.9	17.1	18.7	18.6	17.0	14.1	11.2	9.2
Pembroke	8.9	8.6	9.5	11.2	13.7	16.0	17.7	17.9	16.7	14.2	11.6	9.6
Northern Ireland
Belfast	7.9	8.2	9.5	11.4	14.0	16.3	17.8	17.8	16.2	13.2	10.3	8.3
Larne	7.9	7.8	8.6	9.9	12.0	14.1	15.8	16.1	15.1	12.8	10.4	8.6
Balearic Islands
Ibiza	15.6	15.7	17.7	19.6	22.8	26.8	29.5	30.2	27.3	23.7	19.2	16.5
Palma	14.9	14.8	16.5	18.6	22.2	26.3	29.1	29.6	26.6	23.1	18.7	16.0
Canary Islands
Corralejo	18.1	17.7	17.9	18.3	19.1	20.4	21.5	22.4	22.7	22.2	20.8	19.3
Los Cristianos	17.9	17.8	18.1	18.4	19.4	21.0	23.3	24.0	23.1	22.2	20.6	19.0
Playa Blanca	18.0	17.6	17.8	18.2	19.1	20.4	21.4	22.4	22.7	22.2	20.7	19.2
San Sebastián	18.6	18.3	18.5	18.8	19.7	21.2	22.9	23.7	23.4	22.7	21.2	19.7
Italy
Capri	12.6	12.2	13.3	15.3	18.8	22.6	25.1	25.8	23.3	20.4	17.1	14.0
Casamicciola	12.3	12.5	14.2	16.6	20.5	24.3	26.9	27.6	24.5	21.0	16.9	13.5
Naples	12.4	12.8	15.1	17.8	21.9	25.9	28.7	29.3	25.5	21.6	17.1	13.4
Sorrento	12.3	12.4	14.3	16.8	20.6	24.5	27.2	27.9	24.5	21.1	17.0	13.5
Greece
Paros	13.6	13.5	14.4	16.2	19.1	22.8	24.7	25.1	23.4	20.7	17.6	14.9
Piraeus	13.7	14.7	17.5	21.6	27.1	32.1	34.2	34.0	29.9	24.9	19.5	15.0
Croatia
Dubrovnik	11.3	12.3	15.0	18.1	22.5	26.7	29.6	30.0	25.4	21.1	16.5	12.4
Hvar	11.0	11.0	12.5	14.9	18.7	22.5	24.9	25.3	22.3	19.2	15.8	12.5
Split	10.7	11.2	13.4	16.3	20.6	24.5	27.0	27.4	23.5	19.8	15.6	11.9
Supetar	10.7	11.2	13.4	16.3	20.6	24.5	27.0	27.4	23.5	19.8	15.6	11.9
Malta
Gozo	14.9	14.5	15.1	16.5	19.3	23.0	25.8	26.8	25.2	22.9	19.8	16.7

Average daily low air temperature, °C (1991–2020, ERA5 via Open-Meteo)
Port	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
France
Caen	3.6	3.5	5.0	6.6	9.6	12.4	14.3	14.4	12.0	9.5	6.4	4.1
Calais	3.2	3.2	4.7	6.4	9.4	12.0	14.2	14.5	12.3	9.5	6.3	3.9
Cherbourg	5.1	4.8	6.1	7.5	10.1	12.6	14.6	14.9	13.2	10.9	8.1	5.9
Dieppe	4.0	3.9	5.4	7.2	10.2	12.9	15.1	15.5	13.4	10.7	7.4	4.8
Dunkirk	3.1	3.1	4.7	6.6	9.6	12.2	14.5	14.7	12.4	9.5	6.3	3.8
Roscoff	4.9	4.6	5.7	6.7	9.2	11.7	13.4	13.4	11.9	10.0	7.4	5.5
St Malo	4.0	3.8	5.3	6.6	9.5	12.1	13.9	14.1	12.1	9.9	6.8	4.6
Spain
Algeciras	10.5	10.7	12.1	13.4	15.7	18.5	20.6	21.4	19.8	17.2	13.7	11.8
Barcelona	6.3	6.6	8.6	10.7	14.2	18.2	21.1	21.5	18.6	15.1	10.3	7.2
Bilbao	7.6	7.4	8.8	10.1	12.7	15.4	17.4	18.0	16.1	13.8	10.5	8.4
Santander	8.4	8.2	9.4	10.6	13.2	16.1	18.2	18.7	17.0	14.6	11.4	9.2
Ireland
Cork	6.2	5.9	6.5	7.6	9.9	12.3	14.1	14.2	12.9	10.8	8.3	6.8
Dublin	4.2	4.1	4.8	6.3	8.6	11.3	13.2	13.0	11.3	8.9	6.3	4.7
Rosslare	6.6	6.2	6.6	7.9	9.9	12.2	13.9	14.4	13.5	11.6	9.1	7.4
Netherlands
Amsterdam	2.6	2.4	3.9	6.3	9.6	12.4	14.8	15.0	12.8	9.6	6.2	3.5
Hook of Holland	2.4	2.2	3.8	6.0	9.3	12.0	14.4	14.5	12.3	9.1	5.8	3.2
Rotterdam	2.4	2.2	3.8	6.0	9.3	12.0	14.4	14.5	12.3	9.1	5.8	3.2
Isle of Wight
Cowes	4.5	4.2	5.3	6.8	9.6	12.3	14.4	14.6	12.6	10.2	7.2	5.1
East Cowes	4.4	4.1	5.2	6.7	9.5	12.2	14.3	14.5	12.5	10.1	7.1	5.0
Fishbourne	4.5	4.1	5.2	6.8	9.5	12.3	14.4	14.5	12.6	10.1	7.1	5.1
Ryde	4.5	4.2	5.3	6.8	9.6	12.3	14.4	14.6	12.6	10.2	7.2	5.1
Yarmouth	5.1	4.6	5.6	7.1	9.8	12.6	14.8	15.1	13.4	11.1	8.0	5.8
Scotland
Aberdeen	3.2	3.0	3.7	5.1	7.1	9.9	11.9	12.0	10.5	8.1	5.4	3.3
Ardrossan	3.8	3.7	4.4	5.7	8.0	10.7	12.5	12.4	10.8	8.3	5.8	3.7
Armadale	4.1	3.9	4.5	5.9	8.0	10.5	12.3	12.5	11.2	8.8	6.4	4.4
Brodick	5.2	4.8	5.3	6.5	8.7	11.2	13.0	13.3	12.2	10.0	7.7	5.7
Cairnryan	5.3	5.0	5.5	6.8	8.8	11.2	12.9	13.3	12.3	10.2	7.8	5.9
Castlebay	6.3	5.8	6.1	7.1	8.8	10.9	12.6	13.2	12.2	10.3	8.4	6.9
Craignure	4.5	4.3	4.8	6.2	8.3	10.7	12.4	12.6	11.3	9.1	6.7	4.6
Cumbrae	4.5	4.3	4.8	6.1	8.4	11.0	12.8	12.9	11.4	9.1	6.7	4.7
Gills Bay	4.3	3.9	4.4	5.6	7.3	9.8	11.8	12.1	11.0	8.8	6.6	4.6
Kirkwall	5.2	4.7	5.0	6.0	7.6	9.6	11.5	12.2	11.4	9.5	7.5	5.8
Largs	3.9	3.7	4.4	5.7	8.1	10.7	12.6	12.4	10.8	8.3	5.8	3.7
Lerwick	5.0	4.5	4.8	5.8	7.3	9.3	11.2	12.0	10.9	9.0	7.1	5.7
Lochmaddy	6.0	5.6	5.9	6.9	8.6	10.7	12.4	12.9	12.0	10.1	8.2	6.6
Mallaig	4.1	3.9	4.5	5.9	8.0	10.5	12.3	12.5	11.2	8.8	6.4	4.4
Oban	3.7	3.5	4.2	5.6	7.9	10.5	12.2	12.2	10.8	8.4	5.8	3.7
Rothesay	4.6	4.3	4.9	6.2	8.4	11.0	12.8	12.9	11.5	9.2	6.7	4.8
Scrabster	3.5	3.2	3.9	5.2	6.8	9.5	11.6	11.7	10.3	8.1	5.7	3.6
St Margaret's Hope	5.1	4.6	4.9	6.0	7.6	9.7	11.6	12.3	11.4	9.5	7.4	5.7
Stornoway	4.1	3.9	4.5	5.7	7.4	10.0	11.8	11.7	10.3	8.2	6.0	4.1
Stromness	5.2	4.7	5.0	6.0	7.6	9.6	11.5	12.2	11.4	9.5	7.4	5.7
Tarbert	4.4	4.2	4.6	5.8	7.6	10.1	11.8	11.9	10.5	8.4	6.2	4.4
Uig	5.1	4.9	5.3	6.4	8.2	10.5	12.2	12.3	11.1	9.2	7.1	5.3
Channel Islands
Guernsey	7.8	7.2	7.9	9.0	11.0	13.3	15.3	16.1	15.4	13.5	10.9	8.7
Jersey	6.9	6.4	7.4	8.9	11.2	13.8	15.8	16.5	15.5	13.3	10.3	7.8
Isle of Man
Douglas	6.0	5.5	5.9	7.2	9.3	11.6	13.4	14.1	13.2	11.2	8.8	6.9
Isles of Scilly
St Mary's	8.4	7.9	8.3	9.2	11.1	13.6	15.5	16.0	14.9	12.9	10.7	9.2
England
Dover	4.1	4.0	5.4	7.2	10.0	12.7	14.9	15.2	13.2	10.4	7.2	4.8
Harwich	3.8	3.6	4.7	6.6	9.5	12.4	14.7	15.1	13.1	10.3	6.9	4.5
Heysham	3.5	3.3	4.1	5.7	8.4	11.2	13.2	13.2	11.2	8.8	6.1	3.9
Hull	2.9	2.8	3.9	5.5	8.2	10.9	13.0	13.1	11.2	8.6	5.4	3.2
Liverpool	4.3	4.0	4.9	6.6	9.2	12.1	14.1	14.2	12.4	9.8	7.0	4.8
Lymington	5.1	4.7	5.6	7.2	9.9	12.7	14.8	15.1	13.5	11.1	8.1	5.8
Newcastle	3.0	3.0	3.8	5.4	7.9	10.7	12.7	12.6	10.6	8.1	5.3	3.2
Newhaven	3.2	3.1	4.4	6.0	8.8	11.6	13.7	13.8	11.6	9.0	5.9	3.8
Penzance	7.5	7.0	7.6	8.6	10.6	13.1	15.0	15.4	14.2	12.2	9.9	8.3
Plymouth	4.4	4.1	5.0	6.2	8.8	11.5	13.4	13.5	11.7	9.5	6.9	5.0
Poole	4.6	4.2	5.2	6.7	9.5	12.2	14.2	14.4	12.6	10.2	7.3	5.2
Portsmouth	4.5	4.2	5.3	6.8	9.6	12.3	14.4	14.6	12.6	10.2	7.2	5.1
Southampton	3.3	3.1	4.3	5.8	8.7	11.5	13.5	13.4	11.3	8.8	5.8	3.8
Southsea	4.5	4.2	5.3	6.8	9.6	12.3	14.4	14.6	12.6	10.2	7.2	5.1
Wales
Fishguard	5.3	5.0	5.6	7.1	9.4	11.9	13.8	14.1	12.7	10.5	8.0	6.0
Holyhead	4.9	4.7	5.3	6.7	9.0	11.4	13.4	13.4	11.9	9.8	7.4	5.5
Pembroke	5.9	5.5	6.1	7.4	9.7	12.1	14.1	14.5	13.1	11.0	8.6	6.7
Northern Ireland
Belfast	4.1	4.0	4.7	6.1	8.3	10.8	12.6	12.6	11.2	8.9	6.4	4.5
Larne	5.1	4.8	5.4	6.7	8.7	11.1	12.7	13.1	12.1	10.0	7.6	5.7
Balearic Islands
Ibiza	10.5	10.4	11.8	13.6	16.5	20.3	23.3	24.1	21.8	18.4	14.3	11.7
Palma	10.3	10.0	11.3	13.4	16.7	20.5	23.3	23.8	21.3	18.2	14.2	11.5
Canary Islands
Corralejo	16.8	16.5	16.7	17.2	18.2	19.5	20.6	21.6	21.9	21.3	19.6	18.1
Los Cristianos	16.6	16.4	16.6	17.0	18.0	19.5	21.4	22.1	21.6	20.8	19.3	17.8
Playa Blanca	16.8	16.5	16.7	17.2	18.1	19.5	20.6	21.5	21.8	21.2	19.6	18.0
San Sebastián	17.4	17.2	17.3	17.7	18.6	20.1	21.8	22.5	22.2	21.5	20.0	18.6
Italy
Capri	10.7	10.3	11.4	13.4	16.9	20.8	23.6	24.3	21.5	18.6	15.1	12.1
Casamicciola	8.2	7.9	9.5	11.8	15.6	19.6	22.1	22.8	19.6	16.3	12.7	9.5
Naples	6.7	6.6	8.4	10.9	14.7	18.7	21.2	21.9	18.4	15.0	11.4	7.9
Sorrento	8.3	8.1	9.7	12.0	15.7	19.7	22.4	23.0	19.7	16.5	12.9	9.6
Greece
Paros	11.7	11.7	12.7	14.6	17.7	21.4	23.5	23.9	22.1	19.3	16.0	13.1
Piraeus	6.2	6.7	8.6	11.5	16.0	20.4	23.0	23.0	19.3	15.5	11.5	8.0
Croatia
Dubrovnik	5.9	6.1	8.3	11.3	15.4	19.4	21.7	22.1	18.2	14.5	10.8	7.0
Hvar	8.7	8.5	10.2	12.9	16.8	20.7	23.1	23.5	20.2	17.1	13.5	10.2
Split	6.9	6.7	9.0	12.1	16.2	20.2	22.5	22.9	19.0	15.5	11.8	8.2
Supetar	6.9	6.7	9.0	12.1	16.2	20.2	22.5	22.9	19.0	15.5	11.8	8.2
Malta
Gozo	13.4	12.8	13.7	15.2	18.0	21.5	24.3	25.4	23.8	21.4	18.1	15.0

Where the numbers come from

Sea: monthly mean sea surface temperature for 2023–2024 from the Open-Meteo Marine Weather API, read at the nearest sea cell to each port. Two years is a short record: the API has no sea temperatures before late 2022, so treat these as recent averages, not long-term norms. Hull, Belfast have no sea cell within 25 km, so their rows show a dash.

Air: average daily high and low for each month, 1991–2020 averages, ERA5 via Open-Meteo, read at the ERA5 grid point nearest each port. ERA5 is a reanalysis on a 0.25° grid, so each figure describes that grid cell rather than the harbour itself.

These are averages, not forecasts. Check a forecast before you sail.