Swimming on the Alentejo coast
What the water is actually like along this stretch of the Atlantic, month by month, from a ten-year series measured at Porto Covo: why the sea here is coldest in spring and warmest in October, when the lifeguards are on the sand, and what the temperature does not tell you.
The number
Sea temperature on the Alentejo coast, month by month
These are ten-year averages of sea-surface temperature, measured at Porto Covo, roughly the middle of the Alentejo coast. They describe this stretch of open Atlantic between Sines and the Algarve border. They are not a national figure and they are not the Algarve, which is a different sea with a different answer.
| January | 15.4 °C |
|---|---|
| February | 14.7 °C — the coldest month of the year |
| March | 14.8 °C |
| April | 15.5 °C |
| May | 16.5 °C |
| June | 17.6 °C |
| July | 18.0 °C |
| August | 18.2 °C |
| September | 18.6 °C — the warmest month of the year |
| October | 18.4 °C |
| November | 17.1 °C |
| December | 16.1 °C |
The shape of that table is the thing worth knowing. September and October are the warmest water of the year on this coast, warmer than July. February is the coldest, not January. Nothing here ever gets tropical: the range across an entire year is under four degrees.
Why
Why this coast is colder than the latitude suggests
Two things. The sea lags the air by about two months, which is why the warmest water arrives after the hottest air rather than with it. And through the summer the nortada, the north-westerly that gets up most afternoons, drives upwelling along this coast: cold water rising from depth to replace the surface water the wind pushes offshore.
That upwelling is also why the air here stays around 25 °C in August while inland Alentejo passes 35 °C. The same mechanism that makes this coast comfortable to walk in summer makes the water colder than a map would lead you to expect.
The season
When there are lifeguards, and when there are not
In 2026 the bathing season ran 13 June to 19 September. Outside those dates there are no lifeguards on any beach in the parish. That matters more than usual here, because the warmest water of the year arrives in the fortnight after the lifeguards leave.
So the honest version of "when should I swim on the Alentejo coast" is: the water is best in late September and October, and that is exactly when nobody is watching the sand. Good swimming, not casual swimming.
The honest part
What the temperature does not tell you
This is open Atlantic with nothing between here and America. The swell and the wind build through the autumn, and a calm 18.4 °C morning and a rough 18.4 °C afternoon are not the same swim. We measure water temperature; we do not measure sea state, and we are not going to pretend the number covers it.
Several of the small coves are reached across sand the rising tide takes back, so the state of the tide decides which beaches exist on a given afternoon. If you are choosing a beach rather than a month, the tide times and the beach day planner answer that properly, and the beaches themselves differ more than their distance from each other suggests.
Where the numbers come from
Sources, and what they are not
The monthly figures are ten-year averages of sea-surface temperature for this stretch of coast. The bathing-season dates come from Portaria n.º 204-A/2026/1, published in the Diário da República, which is the national order that sets them, rather than from a tourism page repeating them.
Every dated claim on this site carries its source and the day it was last checked; the full list is on the checked page, where this one appears as the October answer.
Common questions
Swimming on the Alentejo coast, asked plainly
Can you swim on the Alentejo coast in October?
What is the warmest month to swim on the Alentejo coast?
Is the sea colder on the Alentejo coast than in the Algarve?
How cold does it get in winter?
When is the bathing season on the Alentejo coast?
What we have learned here
Things worth passing on
Read them allWe live with this village for part of every year, and some of what that teaches you is not written down anywhere. This is the useful half.
Eating cheaply in Porto Covo
Two places, one number that matters, and a Sunday problem. What the price symbols on a listing site will not tell you.
The day to avoid eating out in Porto Covo
Five places shut on a Tuesday, including two of the best-known tables. Both of the cheap options shut on a Sunday. And for nine of them nobody publishes a closing day at all.
Why we built Blue Cove in Porto Covo
A Portuguese family, a long time away, and a village that keeps pulling us home. What we tried to fix, and the one thing we will not take credit for.
Your base in Porto Covo
Stay at Blue Cove
A 3-bedroom apartment with 3 bathrooms and a private heated pool, sleeping 6, 500 m from Praia Grande and 15 minutes from the Rota Vicentina trailhead. Booked directly with Ivy, who confirms every reservation herself.
Keep exploring
More Porto Covo guides
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All thirteen beaches sorted by swimming, surf, sunset and seclusion.
Plan your beach day
Pick a departure time and get the beach that suits the tide and wind.
Tides today
High and low water today, and which beaches that rules out.
With kids
Calm beaches, rock pools, lifeguards and the family day trips.
Surf
The breaks, the seasons, the wetsuit you need and where to learn.
Checked
Eat and buy
Going further
All of it