WEATHER FORECASTING. 6 1 



of a secondary to the north-west of Cape St. Francis and 

 another north of Port. Elizabeth joined together, no doubt, bv a 

 " col." There were indications of other secondaries further to 

 the east, while the upper tongue of an inverted V was to the 

 south of Knysna and a " sub " over the north-east, and the 

 Transkei. Conditions were, therefore, in favour of rain along 

 the South and East Coasts, on to Natal. The secondaries 

 moved eastward and to the north of Port Elizabeth, where the 

 wind chopped round to the S.W. ; torrents of rain fell, which 

 flooded the Baakens River and caused an immense amount of 

 damage. 



During summer months or even well into winter or spring, 

 rain often falls with pressure low inland and easterly winds 

 blowing along the Coast ; the conditions are high pressure over the 

 Transvaal, high to the south or South Coast, with a loop between 

 open to the west and north-west, but closed to the east; this is 

 the Eastern Province summer rain and thunder loop, and when 

 properly developed seldom fails to bring rain and thunder. The 

 cause, is, no doubt, due to its being the home of innumerable 

 secondaries. 



The writer separates the term " sub "* from that of a 

 " secondary " ; the former is in reality a minor depression with 

 closed isobars, differing from the latter. It is cyclonic in char- 

 acter, and very often will form, deepen and die away without 

 changing its position. Its weather conditions are thunder, hail, 

 snow or gales, according to the season and place. They are 

 common in wide " cols " separating areas of high pressure. 



During most of the year a " sub " rests between Cape Town 

 and Clanwilliam, not a moving one but one which forms, dis- 

 perses and reforms ; and here are developed conditions for 

 thunder, fogs or black south-easters. Should the sea level 

 pressure at Clanwilliam and Cape Town be about the same, wit!" 

 a N.W. wind at the former, W. or N.W. at the latter, and 

 southerly at Cape Point, these indicate a wedge to the north of 

 Cape Town extending from the north-west into the " sub " ; this 

 forms a fog wedge, and is often followed by fogs on the South- 

 West Coast. It also indicates an electrical condition, and should 

 a south-easter spring up it will be a " black " one. 



The circulation of wind is often from the eastward at Cape 

 Agulhas, moving round Cape Point towards the north-west; it 

 thus blows from above the warm Mozambique sea current to 

 the cold Antarctic one, and, as a consequence, fogs are prevalent 

 over the ocean to the west. When a wedge, as before men- 

 tioned, is developed, this current of air is deflected and comes 

 on to the West Coast, carrying its fog producing powers. 



Subsidiary Depression. 



