Answer

Hong Kong has humid, subtropical climate in which there is very little temperature variation between day and night, whereas Tucson has a dry, desert climate in which the temperature variation is large. In Hong Kong in June the average daytime high is 31 $^\circ$ C and the average nighttime low is 25 $^\circ$ C; in Tucson the average daytime high is 37 $^\circ$ C and the average nighttime low is 19 $^\circ$ C. Then there is the variability in each of these figures to consider; the daytime high temperature, for example, typically varies more from day to day in desert climates than in subtropical ones. All in all, the mean temperature tells you very little about what to expect in the way of temperature.