The current heat wave in Belgium has become historic because it has happened so late in the year. The temperature was 30.2Â° at 4pm on Saturday, according to meteorologist David Dehenauw. The Royal Meteorological Institute (IRM) defines a heat wave as a period of five consecutive days with a temperature of at least 25Â°, with at least three "tropical" days. Tropical means at least 30Â° in Uccle, a national reference point. The heat wave started on Tuesday, and is expected to last until Sunday, says David Dehenauw. The temperature is expected to drop to 25Â° on Monday. It's the first heat wave of 2016, as well as the latest and first September heat wave of the 21st century. This is the 9th heat wave in Belgium since the start of the century. The others were in 2001, 2003, 2005, two were in 2006, and the rest were in 2010, 2013 and 2015.