Here is some information about the weather in Israël. I went in august, when a heatwave was there. The temperature in Tel Aviv was then about 38 degrees Celcius, this is not normal for the end of august, it should be between 28 and 35 degrees Celcius at this time. But I got used to it though. In Jerusalem it was 37 degrees Celcius at that time, in Tiberias about 35 degrees Celcius and at the Death Sea, there was a temperature of even 45 degrees Celcius! When it gets dark, it gets very cold in the dessert though! So watch out. You'd better take it easy at the hottest times of the day, which is between 11 am and 2 pm.