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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 33/16
ALLDAYS 27/13
BEAUFORT WEST 31/21
BELA-BELA 27/09
BETHLEHEM 26/05
BISHO 34/14
BLOEMFONTEIN 25/06
CALVINIA 28/16
CAPE ST LUCIA 26/19
CAPE TOWN 21/11
CLANWILLIAM 28/19
DE AAR 27/09
DURBAN 27/14
EAST LONDON 36/18
ERMELO 25/06
FAURESMITH 25/11
FICKSBURG 24/03
GEORGE 24/12
GRAAF-REINETT 31/15
GRAHAMSTOWN 33/14
HERMANUS 20/13
JOHANNESBURG 26/07
JOUBERTINA 29/12
KIMBERLEY 29/10
KLERKSDORP 29/08
KOMATIPOORT 30/13
KROONSTAD 27/08
LADYSMITH 31/07
LANGEBAAN 20/11
LEPHALALE 28/13
LYDENBURG 27/06
MAFIKENG 26/09
MUSINA 28/13
NELSPRUIT 27/08
NEWCASTLE 29/10
OUDTSHOORN 33/12
PAARL 23/14
PHALABORWA 29/13
PIETERMARITZBURG 30/12
PLETTENBERG BAY 26/15
POLOKWANE 26/07
PORT ALFRED 32/15
PORT ELIZABETH 30/14
PORT ST JOHNS 29/18
POTCHEFSTROOM 27/07
PRETORIA 27/09
QUEENSTOWN 27/11
RICHARDS BAY 28/18
ROBERTSON 29/13
RUSTENBURG 27/08
SASOLBURG 28/06
SKUKUZA 31/12
SOWETO 26/07
SPRINGBOK 27/09
STILBAAI 18/12
SUTHERLAND 23/11
TZANEEN 24/10
ULUNDI 32/11
UMTATA 32/11
UPINGTON 30/12
VEREENIGING 28/06
VREDENDAL 24/11
VRYBURG 28/08
WELKOM 26/08
WITBANK 26/07
WORCESTER 28/13

 

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