What do the data found on the internet say?

Based on measurements taken over the past fifty years in the open sea, average values were taken and the following table was created.

Temperature by regions
JUNEJULYAUGUSTSEPTEMBER
TASOS22.8°C26.1°C26.4°C24.5°C
HALKIDIKI24.4°C26.3°C26.6°C24.9°C
KRF23.6°C25.3°C26.9°C26.1°C
LEFKADA22.5°C25°C27.3°C26.4°C
KEFALONIA23.8°C26.1°C27.5°C26.4°C
PELOPONNESE24°C26.6°C27.6°C26.7°C