I measured the Guillamenes at 12.5C yesterday, a full 3.5C warmer than a week previously, sun in the sky, and no wind.
However swimming outward past Newtown Cove the temp dropped, and halfway to the Metalman I’d say it was only about 9.5C.
There was no particular sensation of gradually warmer water as I swam from outside the Metalman, just outside the bay, back inward until after a few hundred meters after I passed the Comolene. There were distinct warm patches from there to the pier.
Overall, maybe because of tiredness, I got cold quickly yesterday and had enough at just under 90 minutes.
It’s almost impossible to gauge what the difference between water temperatures once one is in it. Going on experience I usually guess about a 2 degree differential. Yesterday was a bit more I think.
After I returned to the car park I was surprised that I could see multiple cold streams. Out past Newtown cove I could 4 different stream, and in past the Guillamenes, I could see three. Two are easily visible in the picture, with the third slightly visible over and to the right of the other two. I haven’t seen this before.
I’d guess I can remember the main cold and warm spots in most places I’ve swam.
Some other examples:
Clonea is cold once you swim east past the black rocks below the big house even on warm days.
Baile na Gaul has a cold patch at the point before Helvick.
The temperature drops as you swim over the Gainers, the reefs 2/3 of the way across Dungarvan Bay.
Sandycove is cold as you pass the second corner and mostly warm around the third corner.
Clew Bay is intermittently warm as you swim into the Newtown estuary.
Inishcarragh can have cold spots at the far side of the lake.
I remember them because they hurt.