4. Passage plan

4.1. Hydrometeorological features.

Cape Town

The climate is hot and humid in the equatorial zone in all seasons but tropical cyclones do not affect the region. African coastal temperatures steadily decrease S of about 10_S due to the relatively cold Benguela Current and increasing latitude. Along the African coast, rainfall is abundant in the extreme N of the area and steadily decreases to almost totally dry conditions along the Namibian coast. The SW part of Cape Province is usually warm and relatively dry in summer and cool and wet in winter.

SE Trade Winds dominate the greater part of the area covered by this volume. The exceptions are: the Bight of Biafra, where the winds are mainly S to SW; W of about 1°W between 25° and 35°S, where the winds are very variable; S of around 35°S, where the winds are predominantly from the W.

Over the oceanic islands covered by this volume, the annual rainfall increases from Ascension Island at around 130mm S to Gough Island which records around 3200mm. Fog is rare in the N but hazy conditions often affect the Bight of Biafra. Sea fog can be a hazard in the vicinity of the Benguela Current between 10° and 30°S and often drifts E over the coast, particularly at night.

Strait of Gibraltar and Barcelona

Summer in the W basin of the Mediterranean Sea is frequently hot, particularly in the S, with long periods of fine settled weather. Winters are mild with most of the rainfall occurring in late autumn and winter. The rain is mainly in the form of heavy showers which usually clear quickly and therefore overcast skies are infrequent with good spells of sunshine, particularly in the S of the area. Winds of force 7 and over are rare in summer over most of the W basin except for the Golfe du Lion where they may occur on around 5 to 6 per cent of occasions, and around Corse with a frequency of 4 to 5 per cent. The frequency of gales steadily increases during October and with a maximum frequency occurring over the Golfe du Lion in late autumn and winter.

Table 4.1 – Hydrometeorological features

Title	Unit	Area
		Cape Town	Strait of Gibraltar	Barcelona
Wind direction	CP	S	W	N
Frequency of wind	%	39	32	30
Wind speed	m/s	7	6	4
Gale	day	1	< 1	< 1
Swell	scale	4	3	3
Frequency of swell	%	40	30	30
Max height of wave	m	5	3	3
Average height of wave	m	< 2	1	1
Temperature (Day / Night)	ºC	26 / 15	19 / 13	16 / 8
Average temperature of sea water	ºC	19	20	13
Visibility	mile	5	> 5	> 5
Fog	day	3	1	2
Clouds	oktas	2-3	4	4
Precipitation	mm/year	500	790	650

Table 4.2 – Weather-facsimile charts

№	Radio / station	Symbol and chart area	Content	Time
1	Cape Town Ch 16	NAVAREA VII South Atlantic	Local and coastal warnings	0020, 0420, 0820, 2020
			Coastal weather bulletins	1220, 1620
2	Tarifa Ch 10	NAVAREA II West Mediterranean and North Atlantic	Actual wind and visibility at Tarifa, followed by forecast for Strait of Gibraltar	Every even hour + 15
			Navigational warnings	On receipt
3	Barcelona Ch 10	NAVAREA III	Weather bulletins	0600, 1000, 1500, 2000