Uganda is tropical. The equator passes crosses through it. It is warm though not as humid as our summers here in the US. Light clothes and short sleeves or sleeveless clothes are great in such a hot environment. They are acceptable. Nevertheless, very short dresses or extremely mini shorts would be considered offensive.
Please note that on Sunday mornings, all men would be expected to be in dress clothes including shirt, tie, jacket and dress shoes and women wearing a dress or skirt that comes below the knee.