Month by month
Udzungwa in April
April sits in the middle of what guides call the long rains, with the thirty-year average showing 165 mm of rain over 13 days, less than March but still enough to keep the caution on ambitious trails in force.
If you only want the answer
April is not the month to push the multi-day treks. The short walks near Mang'ula remain fine, the wildflowers and butterflies are near their best, and Mwanihana or Lumemo are better booked for later in the year.
Fewer rain days, same caution
Rain drops from March's 245 mm to 165 mm across 13 days in April, and the temperature eases too, with days averaging 25.3°C and nights 18.8°C, the coolest nights since the dry season last visited. What has not changed is the advice that runs through the whole mid-March to May window: operators caution against attempting the upper tiers of Sanje Waterfall, and the multi-day routes over Mwanihana and the Lumemo Trail carry real landslide risk on their steep sections in this stretch.
If a guide tells you a route is off that day, that is not caution for its own sake. The trails run over exposed roots, loose rock and slick laterite that this rain is actively working on, and an armed ranger's presence on the plateau routes is about elephant and buffalo, not the ground itself, so the ground is entirely your own risk to manage.
What April is actually good for
The short walks near headquarters, Prince Bernhard Falls at a kilometre and Sonjo at three, stay genuinely doable and give you Sykes' monkeys, baboons and forest birds without the exposure of a longer climb. Njokamoni's quieter route to its own waterfall and a decent shot at Sanje mangabey is also a reasonable April choice, carrying less of the loose-rock exposure that the plateau routes do.
April also falls inside the November-to-April window that TANAPA itself rates as its best stretch for wildflower and butterfly photography, and with 250-plus recorded butterfly species in the park, that is a genuine payoff for accepting the wetter footing.
The honest booking advice
If Mwanihana Peak or the Lumemo Trail are the point of your trip, April is the month to push that plan to June rather than force it now. Everything else works the same as always: a guide gets assigned on the day you show up at Mang'ula, and only the special campsites and multi-day trek camps need reserving ahead.