The Met Office says that provisionally the minimum temperature recorded at Aberporth, near Cardigan on Tuesday (Sept 7) did not fall below 20.5 degrees Celsius.
Met Office experts are checking their equipment before making the number official but it looks set to be a clear record.
The previous record had been held by the north Wales beach resort of Rhyl since 1949 with just 18.9 degrees Celsius.
As the temperature did not fall below 20 degrees C the Met Office say that falls into the category of being a tropical night.
The hot weather continued to break records on Wednesday with Scotland breaking a daytime record that was set in 1906.
It's not set to last long however as forecasters say there is a strong chance of their being a thundery breakdown tomorrow (Thursday).