Precursors of summer heatwaves in the Eastern Mediterranean

Reanalysis and observational data are used to identify the precursors of summertimeheatwaves over the Eastern Mediterranean over the historical period. After compilinga list of heatwaves using objective criteria, we identify robust precursors present 7 to 10days before the onset of the heatwave, longer than the typical horizon for trustworthyweather forecasts. If these precursors are present, there is a significant warming overthe Eastern Mediterranean over the following 10 days that then persists for weeksafter. These precursors include a weakened Indian monsoon, warm West/CentralMediterranean Sea surface temperatures, and a low disturbance from the west. Further,horizontal temperature advection is the proximate cause of the heatwave in the daysbefore the extreme, and in particular a weakening of the Etesian winds that wouldotherwise advect relatively cool maritime air inland accounts for around half of thewarming. There is a clear tendency for more heat extremes in recent years. Theseresults have implications for the forecasting of summer heatwaves in the EasternMediterranean, and the framework developed here can be applied in other regions aswell.