Deciding when to come on safari to the Victoria Falls/Kariba/Zambezi area depends on what you are looking for. There are basically four seasons as follows:-
NOVEMBER-MARCH: Summer rainy season:
Hot days (30oC+), and nights (22oC) strong possibility of showers or thunderstorms especially afternoon/evening. Rain cools the temperatures. High winds can occur on Lake Kariba and along the Zambezi River. Dirt roads are muddy and tricky without a 4x4. River crossings are sometimes impassable due to floods. Mosquitoes and other insects are prevalent. Vegetation is lush and green with new growth. Baby animals are in evidence. Butterflies everywhere. Long grass makes game viewing less rewarding. Birding is superb, as the area is full of summer-migrants.
APRIL-MAY: Autumn post-rainy season:
Limited rainfall. Pleasantly warm in the day (28oC) but temperatures cooling off at night (15oC). Mosquitoes still prevalent. Dirt roads now passable. Vegetation attractively green from the rains, but long grass still obscures game viewing.
JUNE - AUGUST: Winter cool-dry season:
Dry, sunny, clear days, (26oC) but can get very cold at night and in the early morning (8oC). No rain. Few mosquitoes. Dirt roads now dry and hard. Good game-viewing as bush and grass now brown and eaten down and animals seek out water sources.
SEPTEMBER-OCTOBER: Spring very hot-dry season:
Very dry and very hot in the day (35oC+) and at night (25oC). Roads very dry, hard and dusty. Air can be hazy because of dust and the smoke from bushfires. Few mosquitoes. Excellent game viewing as the land dries up and wildlife congregates at water sources. Bush parched, brown and leafless, but some vegetation coming into flower.
VICTORIA FALLS - Seasonal flow rates
The flow rate of the Zambezi River over the Victoria Falls varies considerably at different times of the year.
High water levels - January - May: During the rainy season December - April, because of the vast upstream catchment area of the river, and the long way the water has to travel before it arrives at Victoria Falls, it can take some weeks (even months) before the river flow at Falls rises. The water can also continue to be at high levels, even when the seasonal rains have ended!
During these months expect a lot of spray and be prepared to get very wet when walking in the "rainforest" opposite the Falls between January and May. It is also quite difficult to take good photographs of the Falls at this time because visibility is obscured by the constant spray. You will need to wear raingear (you can hire this from your hotel or operator), and make sure you carry your camera and ID documents (for entry to the Falls) in something waterproof.
Low water levels - June - December: From June onwards, the river flows gradually drop until in November-early December, they reach their lowest. Some part of the Falls on the Zambian side of the river actually dry up altogether during this time. However, on the Zimbabwean side, there are magnificent views right down into the bottom of the 100m gorge into which the Falls plunge. These are the driest months for a walk in the rainforest, and the reduced spray will allow for considerably easier photography and beautfiul, clear images.
Seasons of the Southern African Bush - March 2014
Visiting Africa during the Rains - November 2013