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SA REGIONAL




INFORMATION




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BERGWIND

Bergwind is the South African name for fohn wind or mountain wind. It is a hot, dry wind that blows from the interior of South Africa to the coast and usually is blustery. Most people find it rather unpleasant. It can be mild at times blowing at about 10km/h, but sometimes it can be really strong and may gust up to 100km/h causing some structural damage to buildings and uprooting trees.

FORMATION

Bergwinds usually occur when a strong high pressure exists south or south-east of the country and when a high pressure is also situated over the country. These conditions usually only occur in winter, but sometimes in summer too, hence bergwinds are mainly a autumn-winter-spring phenomemon.

Since air rotates anti-clockwise around a high pressure in the southern hemisphere the wind direction to the north of the high pressure will be easterly or north-easterly, especially along the west coast of southern Africa. The bergwinds will usually start blowing along the Namibian coast and the first indication of bergwinds is a rise in temperature, sometimes this rise can be rapid. In winter of 1985 in CT, the temperature rose from 3C at 07:00 in the morning to 27C by 07:35 that SAME morning. This is not a common occurrence, but rather an extreme case.

Since air in a high pressure descends and warms up as it descends it stands to reason that the off-shore winds will be warm to hot and the temperature will usually rise about 10 degrees Centigrade from the interior of SA to the coast. So the temperate at Upington may be 20C, while at Alexander Bay it may be over 30C.

At the same time a coastal low will develop along the coast. Off-shore flow ahead of the coastal low is usually easterly to north-easterly in direction along the west coast and north-westerly along the east coast. Humidities are usually very low, sometimes as low as 5%, usually between 10-40%. The temperatures vary from 25C to 35C in winter and over 40C in summer. Behind the coastal low the wind is on-shore and usually north-westerly to south-westerly in direction. It is cool and moist and usually associated with fog.

The coastal low moves down the west coast and around the Cape Point and then up the east coast of South Africa until it fills up near Maputo in Mozambique. The bergwinds obviously follow the same pattern. The highest official temperatures recorded in South Africa (51.5 C) was recorded one summer during a bergwind occurring along the Eastern Cape coastline.

The bergwinds are usually followed by a cold front in winter.

Click on the minimized diagram below to view an enlarged image of the typical coastal low and bergwinds.


Click to view a larger image.

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ALEXANDER BAY 25/17
ALLDAYS 33/22
BEAUFORT WEST 32/13
BELA-BELA 29/17
BETHLEHEM 29/11
BISHO 27/13
BLOEMFONTEIN 33/18
CALVINIA 35/17
CAPE ST LUCIA 27/22
CAPE TOWN 33/17
CLANWILLIAM 38/20
DE AAR 35/14
DURBAN 27/18
EAST LONDON 23/18
ERMELO 25/12
FAURESMITH 35/16
FICKSBURG 30/12
GEORGE 22/16
GRAAF-REINETT 29/11
GRAHAMSTOWN 26/14
HERMANUS 29/16
JOHANNESBURG 24/15
JOUBERTINA 28/12
KIMBERLEY 35/20
KLERKSDORP 29/16
KOMATIPOORT 34/19
KROONSTAD 32/16
LADYSMITH 26/14
LANGEBAAN 30/20
LEPHALALE 32/20
LYDENBURG 25/16
MAFIKENG 32/18
MUSINA 34/20
NELSPRUIT 28/15
NEWCASTLE 28/14
OUDTSHOORN 34/16
PAARL 35/18
PHALABORWA 34/20
PIETERMARITZBURG 25/12
PLETTENBERG BAY 22/18
POLOKWANE 27/15
PORT ALFRED 23/17
PORT ELIZABETH 24/19
PORT ST JOHNS 26/16
POTCHEFSTROOM 28/16
PRETORIA 25/17
QUEENSTOWN 25/12
RICHARDS BAY 26/21
ROBERTSON 32/13
RUSTENBURG 30/17
SASOLBURG 27/15
SKUKUZA 35/19
SOWETO 23/15
SPRINGBOK 26/14
STILBAAI 25/18
SUTHERLAND 30/12
TZANEEN 27/16
ULUNDI 29/15
UMTATA 25/13
UPINGTON 39/25
VEREENIGING 26/15
VREDENDAL 31/16
VRYBURG 35/20
WELKOM 32/17
WITBANK 25/12
WORCESTER 34/14

 

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