Sea Conditions Guide: Southern Africa

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© 2019 DTN, LLC, all rights reserved. “DTN” and the degree symbol logo are trademarks of DTN, LLC. Subtropical climate highly waters from the Southern Ocean or also called Antarctic Ocean and finally the influenced by the relation South Atlantic Ocean. between three oceans Therefore, the area has sort of three different climates which from the west Southern Africa is a very to the east change from mild and drier to strategic area for the warmer and rainier. maritime industry. Several important ports are located Roaring Forties vs on the Southern Africa South Atlantic High region and most of them The western/southern belt are important for shipping of this area with Cape of routes regarding bunkering, Good Hope being very well sheltering, maintenance known by the worldwide and are hubs for import/ mariners is hugely influenced export at one of the richest by the relation between the economies in Africa. Roaring Forties to the south and the South Atlantic High This region has a subtropical climate with temperatures driven by the sea to the west/northwest. temperatures which are strongly influenced by two main currents, Despite the mild climate across this area Agulhas to the east/south and Benguela the deep Lows over the Forties often to the west. Those currents are result of bring storms and gale winds caused by the interaction between three oceans; strong cold fronts. This happens usually the warm Indian Ocean, deep cold during the winter (June-September). During the summer (December-March) Agulhas Current and weather is dry, often with clear skies but wind speeds tend to be even higher Freak Waves (frequent and persistent gales) due to the tight pressure pattern over the The Agulhas Current coastal areas caused by the South is southwards current Atlantic High-Pressure ridge compressed by the relatively high continental slope. that flows along the Southwestern Indian Ocean This is highly observed along the areas surrounding where those due to ocean recirculation persistent strong winds are locally and strong eddies over known by Cape Doctor or South-Easter and wind enhancement is experienced the Mozambique Channel. due to funnelling between Table This current is often used Mountain and Hottentots-Holland mountains. This local phenomenon also by mariners when sailing produces a well-known cloud band over westwards to improve which is due to the warm and moisty air from being the speed. blown, lifted and cooled throughout the Mountain leading to condensation. The However, there is a particular dangerous wind side over Cape Town is dry with feature along this current which is linked clear skies and blows away part of Cape to low-pressure systems deepening as Town’s pollution and that’s why is called moving across this warm current leading Cape Doctor by locals. to explosive cyclogenesis over the area. The seas that follow these systems, To the Eastern side surrounding Durban when counter direction the current (often the most dangerous weather feature associated with southerly gales over is associated to a strong and deep low- the sea) can be quite unpredictable and pressure trough which extends from the causing freak waves to form that can Forties up to the Eastern and threaten all sort of ships. often with a Coastal Stormy Low located around Eastern Cape. This Low often has potential for creating the popular named feature called Southerly Buster with winds shifting from near calm to gales within a really short period of time.