|
||||
 |
|
Fri, 03 Jul 2009 | |
|
You are in: Weather > SA regional > Ecucation  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 3°C at 07:00 in the morning to 27°C 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 20°C, while at Alexander Bay it may be over 30°C. 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 25°C to 35°C in winter and over 40°C 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. [ back ]
|
 | ||
|
|
|
 | ||
 | ||
|
  |
|
 | ||
 | ||
|
ALEXANDER BAY 25/10 ALLDAYS 18/04 BEAUFORT WEST 18/04 BELA-BELA 17/01 BETHLEHEM 16/01 BISHO 17/08 BLOEMFONTEIN 15/00 CALVINIA 18/02 CAPE ST LUCIA 23/18 CAPE TOWN 22/06 CLANWILLIAM 25/08 DE AAR 16/02 DURBAN 21/13 EAST LONDON 19/10 ERMELO 14/02 FAURESMITH 16/03 FICKSBURG 16/02 GEORGE 19/09 GRAAF-REINETT 19/04 GRAHAMSTOWN 17/05 HERMANUS 19/13 JOHANNESBURG 16/01 JOUBERTINA 20/03 KIMBERLEY 18/03 KLERKSDORP 18/01 KOMATIPOORT 22/10 KROONSTAD 16/00 LADYSMITH 16/05 LANGEBAAN 21/14 LEPHALALE 19/11 LYDENBURG 12/01 MAFIKENG 16/01 MUSINA 19/05 NELSPRUIT 16/06 NEWCASTLE 17/06 OUDTSHOORN 19/04 PAARL 24/08 PHALABORWA 22/07 PIETERMARITZBURG 20/08 PLETTENBERG BAY 19/09 POLOKWANE 16/09 PORT ALFRED 21/09 PORT ELIZABETH 21/07 PORT ST JOHNS 19/11 POTCHEFSTROOM 16/01 PRETORIA 18/03 QUEENSTOWN 15/05 RICHARDS BAY 22/15 ROBERTSON 22/08 RUSTENBURG 20/03 SASOLBURG 16/04 SKUKUZA 21/02 SOWETO 15/01 SPRINGBOK 20/12 STILBAAI 19/10 SUTHERLAND 13/01 TZANEEN 16/08 ULUNDI 21/10 UMTATA 17/07 UPINGTON 20/05 VEREENIGING 17/01 VREDENDAL 27/06 VRYBURG 18/02 WELKOM 17/01 WITBANK 14/02 WORCESTER 22/06 |
|
| ||
|
| DISCLAIMER | FEEDBACK | ABOUT US | ADVERTISING | CONTACTS | SERVICES & PRODUCTS |
©COPYRIGHT 1995-2008, CUSTOMWEATHER,INC
 |
