Berrit (1958) distinguished four hydrographic seasons for the Pointe Noire area. These are:
- a “long cold season” from June to September when waters are cold (less than 20°C surface temperature and high salinity - more than 35.5%)Alfonso Dias (1974) has also observed these hydrographic regimes in the Lobito area.- a “short warm season” from October to December
- a “short cold season” from December to January
- a “long warm season” from February to May, when waters are warm (over 27°C surface temperature and less saline - below 35.5%)
The change from the “long warm season” to the “long cold season” starts in the south and shows a very quick apparent progression from south to north.
At Pointe Noire, Ghéno and Poinsard (1968) also observed the alternation of cold and warm seasons, but according to Baptista (1977) the minimum temperature at Pointe Noire in the cold season is some 2°C higher than that at Lobito.
Figures 3 and 4 show the mean surface isotherms during the first and third quarters (from Merle, 1978).
There is considerable year-to-year variation in the hydrographic conditions: the specific characteristics of each season are much more marked in one year than in another (Berrit, 1958).
