What is Super Typhoon Saola’s ‘double eyewall’? Hong Kong experts say 2 cloud rings typical of very strong storms, seen among half of US hurricanes
- Observatory says ‘eyewall’ refers to thick circular ring of clouds surrounding centre of the storm, where winds are at their fiercest
- Doubling of Saola’s central cloud rings is ‘indicator of intense typhoon,’ experts explain

Super Typhoon Saola’s “double eyewall” is a feature of very strong storms and commonly seen in half of hurricanes in the United States, experts have said, as Hong Kong braces itself for what could be one of the city’s worst weather events in years.
The Observatory upgraded its typhoon signal to No 9 from No 8 at 6.20pm on Friday as the storm skirted within about 30km (19 miles) east of the forecaster’s main facility in Tsim Sha Tsui.
It also said Saola, which is named after a rare and protected horned mammal in Vietnam, had developed a “double-eyewalled structure” as it encroached upon the city.
The Observatory explained that the phrase “eyewall” referred to the thick circular ring of clouds surrounding the centre of tropical cyclones, where winds are at their fiercest.