Month by month
Udzungwa in May
May is where the long rains visibly wind down: the thirty-year average shows rain falling to 134 mm over just 9 days, the first single-digit rain-day count since the dry season ended.
If you only want the answer
May is the transition out of the wet, with real improvement on the trails over April but not yet the firm footing of June. If your dates are flexible, waiting two or three weeks buys you a noticeably drier park.
Fewer rain days, but not gone
Rain days fall from April's 13 to just 9 in May, and the total volume drops to 134 mm, the lightest of any month since October. Days cool to 24.5°C and nights to 17.1°C, almost three degrees colder than January's overnight low, the clearest sign yet that the dry season is approaching from the other direction. The caution about Sanje's upper tiers and the plateau routes still applies through May, but the odds of a clean walking day improve week by week.
This is also the point where the gap between what the calendar says and what the ground actually does opens up. A dry-feeling morning in late May can still sit on trails that took on weeks of saturation through March and April, so a guide's on-the-day judgement matters more here than the monthly average suggests.
What still holds, and what to pack for
The Udzungwa red colobus stays exactly where it always is, in the canopy on Sanje and Mwanihana, unmoved by any of this. What you should adjust is your layers rather than your expectations: overnight lows in the high teens are enough to notice at a trail camp, and the light rain jacket that covered December's storms is worth pairing with something warmer for a May evening.
Leech activity is easing from its wet-season peak but has not dropped to dry-season levels, so gaiters are still worth carrying rather than assuming the worst of it is over.
The honest trade-off
If you can hold your dates loosely, waiting for June buys you the firmest trails of the year with barely a change in cost or crowding, since nothing here books out seasonally the way it does in a game park. If May is what your schedule allows, it is a genuinely workable month rather than a compromise one, provided you keep the ambitious plateau routes on hold and let your guide call the daily conditions rather than the calendar.