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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 24/09
ALLDAYS 19/07
BEAUFORT WEST 15/00
BELA-BELA 19/03
BETHLEHEM 13/03
BISHO 16/01
BLOEMFONTEIN 14/02
CALVINIA 15/01
CAPE ST LUCIA 23/15
CAPE TOWN 17/09
CLANWILLIAM 20/05
DE AAR 16/01
DURBAN 21/09
EAST LONDON 21/09
ERMELO 17/-1
FAURESMITH 16/00
FICKSBURG 15/02
GEORGE 15/08
GRAAF-REINETT 19/03
GRAHAMSTOWN 20/04
HERMANUS 17/05
JOHANNESBURG 17/00
JOUBERTINA 17/02
KIMBERLEY 19/01
KLERKSDORP 20/01
KOMATIPOORT 23/09
KROONSTAD 17/01
LADYSMITH 20/00
LANGEBAAN 17/04
LEPHALALE 21/06
LYDENBURG 17/02
MAFIKENG 18/01
MUSINA 21/07
NELSPRUIT 19/02
NEWCASTLE 20/01
OUDTSHOORN 19/02
PAARL 18/04
PHALABORWA 23/08
PIETERMARITZBURG 22/02
PLETTENBERG BAY 17/06
POLOKWANE 18/02
PORT ALFRED 20/09
PORT ELIZABETH 18/10
PORT ST JOHNS 22/09
POTCHEFSTROOM 19/00
PRETORIA 17/02
QUEENSTOWN 16/00
RICHARDS BAY 23/11
ROBERTSON 18/01
RUSTENBURG 19/03
SASOLBURG 18/00
SKUKUZA 23/09
SOWETO 17/00
SPRINGBOK 17/01
STILBAAI 16/07
SUTHERLAND 14/01
TZANEEN 18/03
ULUNDI 22/04
UMTATA 21/02
UPINGTON 22/03
VEREENIGING 17/-1
VREDENDAL 17/03
VRYBURG 20/02
WELKOM 18/01
WITBANK 17/-1
WORCESTER 19/03

 

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