At current time (around 20:30 UTC) it has been observed that no glacier flood has started in Skaftá river. But the glacier flood is expected to start in the river around midnight, but the river might start to grow around 19:00 to 21:00 UTC. According to latest news the river has however started to get darker and conductivity in the water has started rise since this morning, but that was the signal that a glacier flood was about to start. Glacier flood tremor have also been dropping in the last few hours according to the latests news that I have seen (but I am hoping for a update on that detail).
The source of this glacier flood is a hydrothermal area in Hamarinn volcano (part of Bárðarbunga volcano). This area also did have a glacier flood last year. But last year there where two glacier floods in Skaftá river in June 2010, see reports here in Iceland at Icelandic Met Office web page.
This hydrothermal area in Hamarinn volcano is in two cauldrons in the Vatnajökull glacier. With time they fill with water that then breaks ice when the pressure is enough in the cauldrons due to water levels. It remains a question if the surprise glacier flood earlier this month from Hamarinn volcano has something to do with this. But at current time that is only speculation. But if the hydrothermal area is unusually highly active, or there has been some change it is hard to know for sure the size of this glacier flood.
Currently however the experts are expecting a small glacier flood due the fact there where two glacier floods from this area last year. But we however have to wait until midnight until we know what is the actual size of this glacier flood.
Icelandic News about this