Excerpts from "A Traveller's Guide to Swaziland" by Bob Forrester.
CARS and DRIVING
Index to information in the guide
Swaziland's climate is subtropical, with the wet season in summer from September to March when about 75 percent of the rainfall occurs. The country has four distinct climatic zones which coincide with changes of altitude: the higher the area, the greater the rainfall. As a rule of thumb, there is an increase of about 75 mm for every 100 meters climbed. Altitude also has an effect on temperature: the temperature drops on average by 0.5 degrees Centigrade for every 100 meters increase in altitude.
Generally, the most clement zone is the middleveld. Not surprisingly, this is where most of the population live and where most of the hotels are situated. You can expect good weather all year round: the winters are warm in the day and cool to cold at night. The sun is virtually guaranteed to shine every day in a cloudless sky for five months of the year, from May to September. Summer has hot days and balmy nights, often with impressive thunderstorms in the late afternoon. Even when it rains, summer days are not usually cold.
Rainfall in the highveld is generally around 1000 to 1250 mm a year, with a few (hotel free) areas receiving higher rainfall. The middleveld receives about 900 to 1000 mm of rain a year; the lowveld receives less than 800 mm, about one-third of the area receiving less than 650 mm rain. The figures can be misleading because rain in the middleveld and lowveld tends to fall in storms and the area is relatively mist free. The highveld, however, can be drizzly and misty for days at a time in the summer. Those unused to very high temperatures would do well to avoid the lowveld in mid-summer where temperatures have been recorded at well above 40 degrees centigrade. Snow occasionally falls in the highveld, every ten or twenty years, although in the late 1990's it fell twice in a few years.