Understanding the variability of solar radiation and surface temperature is crucial for energy planning, agriculture, and climate research. East Africa is one of the most climatically diverse regions in the world. In regions such as East Africa, where climate-dependent sectors dominate livelihoods, understanding the behavior of these variables is especially critical. This study investigates the seasonal and inter-annual variability of All-sky Solar Irradiance and Near-surface Air Temperature (T2m) across five key East African countries: Ethiopia, Kenya, Sudan, Tanzania, and Uganda, using NASA POWER reanalysis data spanning the period 2021–2024. Results from the monthly and annual mean data reveal distinct regional patterns. Sudan consistently exhibits the highest annual mean irradiance and temperature. Ethiopia and Kenya exhibit bimodal irradiance structures, with marked reductions during the mid-year rainy seasons. In contrast, Tanzania and Uganda maintain the lowest annual mean irradiance and temperature. Critically, all five countries share a pronounced irradiance trough in July, corresponding to peak cloud cover during the Northern Hemisphere summer monsoon season. Inter-annual variations in both irradiance and temperature are minimal across all countries, indicating stable climatic forcing and reliable long-term solar resource availability across the region. These findings contribute to understanding the radiative energy balance and potential for renewable energy utilization in East Africa.