It's unclear where you mean by 'dominican'.
If you mean the island of Dominica, you can expect daytime maximum temperatures of around 28C, falling to 22C overnight. Average monthly rainfall is around 160mm (compared with 79mm for London), which suggests that the humidity will be quite high.
Source:
http://uk.weather.com/weather/climatology/DOXX 0001
If you mean the Dominican Republic, you can still expect maximum daily temperatures of around 28C but overnight temperatures fall to around 18C. Average monthly rainfall is 51mm.
Source:
http://uk.weather.com/weather/climatology/DRXX 0008?dayofyear=1
Chris