Marine Climate Signal
Yellow signal on the Cádiz coastal strip in October 2026: 25 days of marine heatwave
Written by Eduardo Garcia · Co-founder / CEO / CTOPublished 15 November 2026
#Marine-Climate-Signal#Cádiz#Spain#October-2026
From 2 to 31 October 2026 the Cádiz coastal strip, in Andalusia by the Strait of Gibraltar, showed a yellow Marine Climate Signal.
The sea carried a marine heatwave for most of the month and mean water temperature sat above what was usual vs 1971–2000. Optical water clarity off the coast stayed on the clear side.
If you live on this coast or work on a harbour, beach or bay, this reading separates anomalous sea heat from how the water looks optically. It does not speak of bacteria or bathing rules.
Sea temperature and marine heatwave
Mean sea surface temperature in the period was 21.31°C. The daily minimum reached 18.19°C and the maximum 23.55°C.
Against the 1971–2000 reference period, mean anomaly for the month was +1.31°C. The anomaly map shows where that extra heat concentrated off the coast.
From 2 to 26 October there was a marine heatwave: 25 consecutive days of anomalous heat in the sea. Peak anomaly in that stretch was +1.75°C.
Sea surface temperature from 2 to 31 October 2026 on the Cádiz coastal strip. The scale runs from the period minimum to maximum.
Sea temperature anomaly vs 1971–2000 in the same period. Warm tones mark where the sea sat above what was usual on those dates.
Daily series from 2 to 31 October 2026. The temperature line follows anomaly vs 1971–2000 on the same calendar.
Period summary: mean 21.31°C, percentiles P10 19.89°C, P50 21.3°C and P90 22.72°C, anomaly +1.31°C and 25 marine heatwave days with peak +1.75°C.
Optical water clarity
Clarity is optical: it measures how murky the water looks in cells off the coast, not sanitary quality.
Mean clarity index in the period was −0.573. The usual range of cells, from the 10th to the 90th percentile, was −0.926 to −0.293.
On this scale, negative values sit on the clearer side of the balance at zero. That usual range sat clearer than the balance, so the clarity reading was good.
Optical water clarity from 2 to 31 October 2026. Tones show whether cells look clearer or murkier vs the balance at zero.
Clarity summary: mean −0.573 and usual range P10 −0.926 to P90 −0.293, on the clear side of the balance.
Why the traffic light was yellow
The traffic light sums two readings: anomalous marine heat and usual optical water clarity.
Green means both are good. Red means both are bad. Yellow means only one is bad.
In October 2026 the marine heatwave pushed heat to the bad side and usual clarity stayed on the clear side. That is why the result was yellow.
Full traffic-light rules are on methodology.
How October was measured
The reading covers the Cádiz coastal strip from 2 to 31 October 2026. Sea heat is compared with the 1971–2000 reference period.
Optical clarity uses 38,099 cells off the coast and 77 useful cloud-free views in that period.
The maps and cards above are the result of that cut. Traffic-light and measure detail sit on methodology. Other coasts and months are on our blog.
- Marine heatwave
- An event of anomalous heat in the sea in the period read, not a single-day spot temperature. Here it lasted 25 days, from 2 to 26 October 2026.
- Heat anomaly
- Difference between sea temperature in the period and what was usual on the same calendar dates in the 1971–2000 reference period.
- Optical clarity
- Reading of how murky the water looks in cells off the coast, compared with the balance at zero between clearer and murkier water.
Conclusion
In October 2026 the Cádiz coastal strip sat on yellow: a 25-day marine heatwave and optical clarity on the clear side.
Knowing this, which beach or stretch of this coast would you like to be on next October?
Questions
What do I do with this signal?
It sums sea heat and optical clarity for that coast on those dates. The question is which beach or stretch of this coast you would like to be on next October. It does not replace a lab sample or bathing rules.
What is the Marine Climate Signal?
A green, yellow or red summary of sea heat and optical water clarity for a coast and dates you choose. This note is the Cádiz coastal strip from 2 to 31 October 2026.
What does yellow mean in this reading?
Only one of the two readings was bad. In October 2026 there was a marine heatwave and usual water clarity sat on the clear side of the balance.
Does clarity say if water is safe for bathing?
No. It is an optical murkiness reading. It does not measure bacteria or apply the EU bathing-water directive.
What is the 1971–2000 reference period?
The stretch sea heat is compared with on the same calendar dates. It shows whether the month moved away from what was usual on those dates.
Talk about your coast
If your stretch of coast is not here, write with the place and the month. We set up the same reading.
Talk to us