Remarkably temperate conditions prevail all the year round, mainly because of the country’s altitude.

RHODESIA, although  lying  in  the heart of South-Central Africa, enjoys a  surprisingly  comfortable climate – surprising,  that is,  to visitors from  northern climes  who associate  the tropics with oppressive  heat and humidity. In fact, a visitor to Rhodesia is likely to find many unexpected features in its climate and weather.

Remarkably temperate conditions prevail almost all the year round, mainly because of the country’s altitude. Every 300-metre climb   brings   a decrease  in temperature of   one   to   two   degrees Celsius, and more than  half of Rhodesia lies over 900 m above sea level, with the main centres of population being between  1 200 and  1 500 m.

Because of Rhodesia’s inland position the  humidity  rarely becomes uncomfortably  high,  the  eastern  border  being about 160 km from the Indian Ocean, while  the  Atlantic  lies about  1 200 km to the west.

Reduced humidity means fewer clouds and more abundant sunshine. But even sunshine can be excessive, and Rhodesia   is  fortunate  that   the   mid­ summer months of December, January and  February coincide   with  the  main part  of the rainy season, when a certain amount  of  cloud   prevents  excessively hot conditions.

Rainfall in tropical countries is basically intense. Yet  the  overall  totals in Rhodesia   are  not  excessive.  The country as a whole  has a mean  annual rainfall  of about  685 mm (ranging from half this  value in  the  extreme  south  to about double at places on the eastern­border  mountains). The  United Kingdom    and    much    of   Europe   record similar   annual   totals; and  New  York, Rio  de Janeiro, Tokyo, Melbourne and Durban  actually   have  higher  average rainfalls than do most parts of Rhodesia.

Nevertheless, it  is  in  respect  of temperatures that  the  biggest surprises are found. The mean annual temperatures  at  the  four  main  centres ­ Salisbury, Bulawayo, Gwelo and Umtali – fall within the range of 17 to 19,5°C.

This  is about  the  same as at  Sydney, Los Angeles and Cape Town, only slightly warmer than average temperatures  at  Athens, Johannesburg, Rome, Lisbon,  Melbourne, Mexico  City  and Buenos Aires, and  slightly  cooler than those  at  Durban and  Brisbane.  Rhodesia is of course appreciably  warmer, on  average,  than  New  York,  London and Paris, but much cooler than Rio de Janeiro,   Miami,  Trinidad,  Mauritius and Dar-es-Salaam.

The  warmest weather actually occurs during  the two – or three – month period immediately before the rainy season. The  warmth itself is. nearly always dry, furthermore, this is a pleasantly breezy time of the year.

During  the  winter  months  the weather   is   predominantly    fine   and sunny and  the  days are  mild. But the nights are surprisingly cool, and even scattered   light   frost   can   sometimes occur on mid-winter mornings.

Temperature graph for main Rhodesian centres
This graph of month-by-month 2pm temperatures (an average for the main centres of population) shows clearly how the cloud cover of the main rainy season prevents temperatures from becoming excessively high during the mid-summer months. The dotted line suggests the climbing temperatures that might occur if this were not so.

Let’s  take  a closer look now  at  the climate, season by season. Both temperature and rainfall are taken into account in  defining   the   Rhodesian    seasons, because they do not conform readily to the popular subdivision into summer, autumn, winter and spring.

Winter is the only real exception. In Rhodesia  we call it the  cool season. It lasts from about  the middle  of May to the middle of August, a total of three months.  Unlike  countries  in  temperate latitudes,  there  is little  difference  here in  the  length  of day  between  summer and winter, and Rhodesia actually has more hours  of sunshine  per day in  the cool  season   than   during   the   period which  conventionally would  be known as summer!

The mild  sunny days  contrast quite sharply,  however, with  conditions at night. The dryness of  the  atmosphere is  mainly  responsible for  a wide  range between the mid-afternoon maximum temperature and  the minimum reached by  early  morning. The difference frequently amounts to more than 15 degrees Celsius.

Warm coats are  therefore commonly  worn  if one  goes  out  at  night. And if one stays at home one is almost certain    to   make   use   of   the   electric radiator, or a log or coal fire (most Rhodesian homes have fireplaces). Pullovers and  cardigans are often  worn during the  first  few  hours  of  the morning and  slipped  on  again  towards evening.

With   the   variations   in   altitude  in Rhodesia, from  Salisbury at  1 500  m, Bulawayo at 1 400 m, the Victoria Falls at 900 m and  Kariba  at 760 m, temperatures  over  the  whole  country do  vary. For this reason, resorts in the low-lying (and  therefore warmer)  parts  of the country   are   naturally   very    popular during the cool season.

The fine mild weather is interrupted from  time  to time  by invasions  of cold air   from   temperate latitudes. The north-western half of the  country is hardly   ever   affected,   but   the   south­eastern and eastern parts may experience occasional  spells  of  cold  overcast weather, with  drizzle  or  rain.  On  the windward slopes  of  the  Eastern High­ lands, the  rain  can  be  quite  heavy  on such  occasions,  but  other   areas  rarely get more than intermittent light drizzle. In extreme  cases, daytime  temperatures may drop  to about 10 degrees C below average for a day or two. Surprisingly though, there   is  usually   a  temporary rise in the temperature at night!

Cold   air   may   also  reach   Rhodesia from  the south-west, that  is, by an overland  route. Even though a south­ westerly  airstream may  bring  snow  to parts  of South Africa, it is always very dry  by  the  time  it  arrives  here.  With skies remaining clear, the daytime temperatures usually  fall only a few degrees. But it becomes much colder at night, and   fairly   widespread  frost   is likely  to occur  under  these  conditions, the south-west of the  country being  of course the most vulnerable.

Very  occasionally, during  the  cool season  there  may  be  an outbreak of thundery rain,  but  these  conditions are extremely short-lived.

From the middle of August there is generally  a definite upward trend in temperature, and   the   transition  from cool   season   to   warm   season   seldom takes more than three weeks!

The temperature rise during September   is  liable   to  be  interrupted  by  a further cold snap  but  the  warm  season is   usually   approaching  its   peak   by mid-October. By then  the ladies have stored  away  all their  woollen garments, and are wearing  gay cotton frocks.  The gentlemen also  respond  to the rapid change from cool to warm weather – smart  “safari suits”, with either   long  trousers   or  shorts, are popular and  may  be seen in all but  the most  conservative of  establishments at this time of the year.

The  rapidly  rising temperatures have a remarkable effect on  the trees as well. The    msasas   become    most   attractive with  their  flush of red or  russet  foliage (which    gradually   changes    to   green   during  the    weeks   that    follow);    in addition, the  jacaranda  and  flamboyant trees  burst  into  bloom in quick  succession.    These  colourful    displays    take place long before any rain has fallen.

Scattered   afternoon   showers    and thunderstorms may occur, however, during the latter half of the warm season. Although rainfall amounts are mainly small, these isolated storms can be quite violent, being accompanied by strong squalls of wind.

The  resorts  along  the  Eastern Highlands  (Inyanga, Melsetter, Vumba)  are popular   during  the   warm  season   because of the lower temperatures associated with their altitude.

Towards  the   end   of  November or early   in   December   the   main   rainy season  begins.  The   onset  of  the  main rains is closely linked  with the arrival of the  so-called   “I.T.C.Z.”.  This stands for  the  Inter-Tropical  Convergence Zone  which  migrates  north and  south as  it   “follows  the   sun”, and   which favours  the development of rain and thunder conditions. It usually  extends across the northern half of Rhodesia intermittently for  three  or four  months of the year.

Wet  and  dry spells  tend  to alternate, each usually lasting a few days. Occasionally, however, a mild wet spell or a warm dry one  may go on rather longer. Although afternoon or evening  thunder storms  are still the predominant form of precipitation,   rain    quite    often    falls during the  night  and  in  the  early morning. This is  particularly the  case when   “Congo Air” is   present. This air-mass reaches Rhodesia  by way of the Congo  and  Zambia,  but  actually  starts off from the South Atlantic Ocean.

Rhodesian weather  is periodically affected  by tropical  cyclones. These intense  revolving   storms,  often   hundreds of miles in diameter, which in the North Atlantic are known as hurricanes and in the China Seas as typhoons. A cyclone  in  the  Mozambique Channel exerts a most surprising influence  on Rhodesian conditions; more  often  than not  it  produces  a spell  of dry  weather! Very occasionally (about once every two are intense  revolving   storms,  often   hundreds of miles in diameter, which in the North Atlantic are known as hurricanes and in the China Seas as typhoons. A cyclone  in  the  Mozambique Channel exerts a most surprising influence  on Rhodesian conditions; more  often  than not  it  produces  a spell  of dry  weather! Very occasionally (about once every two or   three    seasons)    a   cyclone    moves inland. Heavy  downpours and  strong winds are  then  liable  to occur  at  places within about 80 km of the central vortex.

Fortunately, the  overland  movement tends  to  weaken  the  disturbance, and by the time a cyclone enters Rhodesia  it has but a fraction  of its original intensity Rhodesians are  fascinated, rather than awed,  by cyclone  movements reported in the weather forecasts. The practice of allocating  feminine  code-names to cyclones  has  probably  fostered  this attitude.

Day-to-day temperatures show little variation  throughout the  main  rainy season and, on average, they tend to run several  degrees  lower  than  in  the preceding warm season.

This does not apply, however, to areas near Rhodesia’s southern borders which experience only fringe effects of the l.T.C.Z.’s presence.  Cloudiness and rainfall thus do not exert the same modifying   influence   as  further north, with the result that in the extreme south the mid-summer months are actually the hottest.

With   the   northward  retreat  of  the I.T.C.Z. around  March, Rhodesia’s main rainy season draws to a close. If the rains  end  prematurely, a  minor  warm  season  may follow;  but, in  general,  the post-rainy season  is  largely  transitional between  the  main  rainy  season  and  the cool   season; and   it   usually   provides some   of  the· loveliest   weather   of  the whole year.

Written by: J.B. Hattle – Dept. of Meteorological Services

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