Western parks such as Gombe, Mahale and Kavati are likely to have continuous rain throughout the wet season so are perhaps best avoided during this time. Trekking surfaces can become muddy and sometimes even impassable during this rainy season so chimpanzee treks are more difficult.
If you want to combine your safari trip to Tanzania with a beach visit, January is a good time to head to Zanzibar. Although it can be very humid in Tanzania during the wet season, the sea breeze in Zanzibar tempers the climate making it a pleasant place to get some winter sun. We would recommend booking accommodation with air-conditioning though as evenings can be sultry.
Late January sees the calving season begin with antelope, zebra and wildebeest delivering their offspring while the landscape is green and there is plenty of water in the parks. Some of the parks surrounding Ndutu can get very busy during this time so be sure to book your accommodation in advance.