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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 32/18
ALLDAYS 27/15
BEAUFORT WEST 27/11
BELA-BELA 29/16
BETHLEHEM 21/10
BISHO 21/12
BLOEMFONTEIN 29/14
CALVINIA 33/15
CAPE ST LUCIA 22/20
CAPE TOWN 26/15
CLANWILLIAM 32/17
DE AAR 30/15
DURBAN 20/18
EAST LONDON 20/17
ERMELO 21/10
FAURESMITH 29/16
FICKSBURG 24/11
GEORGE 26/14
GRAAF-REINETT 24/10
GRAHAMSTOWN 22/14
HERMANUS 25/14
JOHANNESBURG 25/13
JOUBERTINA 23/14
KIMBERLEY 31/19
KLERKSDORP 26/15
KOMATIPOORT 21/16
KROONSTAD 27/14
LADYSMITH 17/11
LANGEBAAN 28/17
LEPHALALE 27/16
LYDENBURG 21/13
MAFIKENG 29/16
MUSINA 27/15
NELSPRUIT 21/12
NEWCASTLE 19/12
OUDTSHOORN 26/13
PAARL 30/11
PHALABORWA 26/17
PIETERMARITZBURG 17/13
PLETTENBERG BAY 24/14
POLOKWANE 23/13
PORT ALFRED 22/14
PORT ELIZABETH 21/16
PORT ST JOHNS 19/14
POTCHEFSTROOM 27/14
PRETORIA 27/14
QUEENSTOWN 22/11
RICHARDS BAY 21/19
ROBERTSON 30/12
RUSTENBURG 27/16
SASOLBURG 26/14
SKUKUZA 22/16
SOWETO 24/13
SPRINGBOK 35/18
STILBAAI 23/15
SUTHERLAND 29/12
TZANEEN 23/14
ULUNDI 17/16
UMTATA 17/12
UPINGTON 36/22
VEREENIGING 26/14
VREDENDAL 33/19
VRYBURG 30/17
WELKOM 28/14
WITBANK 25/12
WORCESTER 30/12

 

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