Botswana is landlocked far from the coast and mostly in the tropics. It receives a lot of strong sunlight and most of the country is classed as either semi-arid or arid (the line being crossed from semi-arid to arid when evaporation exceeds rainfall). In many respects, most of central and northern Botswana has a sub-tropical 'desert' climate, characterised by a wide range in temperature (from day to night and from summer to winter), and by low rainfall and humidity.
Botswana's climate follows a similar pattern to that found in most of southern Africa, with rainfall when the sun is near its zenith from November to April. The precise timing and duration of this is determined by the interplay of three air-streams: the moist 'Congo' air-mass, the northeastern monsoon winds, and the southeastern trade winds. The water-bearing air is the Congo air-mass, which normally brings rain when it moves south into Botswana from Central Africa. Effectively a belt of rain works its way south across the continent, reaching its southernmost point around January or February. If you listen to any local weather forecasts, they'll probably refer to this as the Intertropical Convergence Zone, or simply the ITCZ. As the sun's intensity reduces, the Congo air-mass moves back north, leaving Botswana dry by around April. Most areas receive their heaviest rainfall in January and February. The rainfall is heavier in the north and east, and lighter in the south and, especially, the southwest.
are the wettest months, when many areas will have regular and often torrential downpours in the late afternoon. When there are no clouds, temperatures can peak as high as 40˚C. However, it's much more usual for them to be moderated by afternoon cloud cover and to stay between about 20 and 30˚C. Humidity fluctuates during the day, typically from about 50 to 80%.
the rainfall is decreasing, though still the afternoon clouds are around. Mornings and early afternoons will often be cloudless, and a few of the nights will go below 10˚C even though the average of the nightly minimums is nearer 18˚C.April
are lovely months. You may catch the odd afternoon shower in April, but these are gone by May – as are most of the clouds. The maximum day temperatures are around 33˚C, and while the nightly minimum average is between 10–15˚C, this hides the occasional chilly nights when areas of the Kalahari will record temperatures just below freezing.June
are the coolest months, with daytime average highs around 25˚C concealing the occasional day when the mercury just reaches 30˚C. You'll still need your shorts, T-shirt, sun-hat and sun-cream for the middle of the day, but as dusk approaches you'll quickly need warmer clothes. The average night goes down to about 6˚C, but cold snaps of well below freezing (typically –5˚C) are common – especially in the drier areas of the Kalahari. August
is very similar, though not quite as cold. You'd be very unlucky for it to go below freezing, even at night, and the days will often creep over 30˚C.September
are really the heart of the dry season, and the daytime heat gradually builds as these months wear on. Typical early afternoon temperatures are in the low 30s (˚C), and nights will seldom fall below 10˚C – and most will be nearer to 20˚C. The humidity is usually very low, typically 20–40%.November
is always interesting and can be unpredictable. Often much of it will simply be a continuation of October's heat and dryness. But eventually the humidity will build and clouds start to appear in the afternoons. These will block the sun, cool the temperatures, and eventually produce some showers in the late afternoon. November mornings will generally remain fine and hot, with blue skies.
the temperatures will usually stay around 20–30˚C, day and night, and rain will be an increasingly regular occurrence in the afternoon. Humidity is normally 50–60%. The hottest days may just reach 40˚C, but even so the coolest nights won't go below about 10˚C.