Luanda has a hot semi-arid climate (Köppen: ''BSh''), bordering upon a hot desert climate (''BWh''). The climate is warm to hot but surprisingly dry, owing to the cool Benguela Current, which prevents moisture from easily condensing into rain. Frequent fog prevents temperatures from falling at night even during the completely dry months from May to October. Luanda has an annual rainfall of , but the variability is among the highest in the world, with a co-efficient of variation above 40 percent. The climate is largely influenced by the offshore Benguela current. The current gives the city a surprisingly low humidity despite its low latitude, which makes the hotter months considerably more bearable than similar cities in Western/Central Africa. Observed records since 1858 range from  in 1958 to  in 1916. The short rainy season in March and April depends on a northerly counter current bringing moisture to the city: it has been shown clearly that weakness in the Benguela Current can increase rainfall about sixfold compared with years when that current is strong.