Weather warnings

A public warning system is a symbol system with an unusual property: it is not describing the weather, it is instructing a city. Hong Kong runs two of them side by side and they do not share a grammar — wind speaks in numbers and hoisted shapes, rain speaks in colour — and a resident reads both without effort.

Grammar: Two grammars in one jurisdiction. Wind is ordinal and shaped: Standby ⊤ a T, Strong Wind ⊥ the same T inverted, four Gale or Storm signals, Increasing Gale ⧗ two triangles meeting point to point, and Hurricane ✚ a cross. The four No. 8 signals carry a two-bit code — apex up means north, apex down means south; one triangle means west, two mean east — so a single ▲ is northwest and a doubled ▼▼ is southeast. Rain is chromatic and measured: amber above 30 millimetres in an hour, red above 50, black above 70. The wind numbers are not a scale — 2, and 4 through 7, do not exist.
Governance: The Observatory issues; the city obeys. Above No. 3 the government, schools, exchange and most employers close, and at No. 9 or No. 10 above-ground rail stops — which is why the ladder is discontinuous: the steps mark thresholds of civic shutdown, not increments of wind speed. That is also its weakness. In July 2001 the Observatory held No. 8 through a day for a typhoon whose gale zone proved small; business bodies put the cost of the unnecessary shutdown in the billions of Hong Kong dollars and the Chief Secretary joined the criticism. The Observatory became measurably more reluctant afterwards, and the caution produced its own failures in 2002 and 2006. A signal that closes a city acquires a price, and an issuer facing a price begins to hedge. Macau runs an almost identical numbered system; the Philippines runs 1 to 5; Bangladesh and India hoist numbered port signals. Most of the world took the other road and encodes severity as colour.
Members: Eight cyclone signals — 1, 3, 8NW, 8SW, 8NE, 8SE, 9, 10 — and three rainstorm colours, alongside the Strong Monsoon Signal, thunderstorm, landslip, very hot and cold weather, frost, fire danger and tsunami warnings. At their height in the 1960s the signals were hoisted at as many as 42 signal stations across the territory, with white, green and red lamps after dark for the benefit of fishermen. The gaps in the numbering are the fossil record: signal 2 went obsolete in 1935, signal 4 was defined for typhoons that never threatened Hong Kong, and 5 through 8 were folded into the modern quartet in 1973.

§Its members

Stand-ins drawn from geometry. Hong Kong's signals are not encoded — they were physical objects hoisted on a mast until 2002, and they have never been characters.

Sources · 10

documented Hong Kong Observatory, Rainstorm Warning System: amber, red and black, issued on rainfall exceeding 30, 50 and 70 millimetres in an hour.
documented Observatory signal definitions: No. 1 for a cyclone within about 800 km; No. 3 strong winds 41–62 km/h; No. 8 gale 63–87 and storm 88–117 km/h; No. 10 hurricane force from 118 km/h.
documented The shapes are the 1917 objects, unchanged. The numbered system began on 1 July 1917 with seven signals hoisted as solid forms: a red upward cone for standby, a black upward cone for a gale from the north, a black downward cone for the south, a black cylinder for the east, a black sphere for the west, two black cones set point to point for an increasing gale, and a black cross for hurricane. Today’s No. 9 and No. 10 are those last two, drawn flat. The up-for-north and down-for-south convention in the modern No. 8 quartet is the 1917 cone convention surviving intact.
documented The 1973 renaming, and its reason. From 1 January 1973 signals 5 to 8 were renamed 8 Northwest, 8 Southwest, 8 Northeast and 8 Southeast. All four had always meant the same wind strength differing only in direction — but the public persistently read the ascending numbers as ascending severity. The renaming exists to destroy a false ordinality the notation itself had created: a symbol system revised because its own grammar misled the people it was built for.
documented Before 1884 there were guns. A typhoon gun was fired once at gale force and twice if hurricane force was expected; from 27 May 1907 detonated charges replaced it, accompanied by a cross-shaped signal, last used in 1937.
documented The 1884 origin: a signal station at the Water Police headquarters in Tsim Sha Tsui — now 1881 Heritage — hoisting cylinders, spheres and cones to show a cyclone’s presence and rough position.
documented The numbering history: seven signals from 1917, ten from 1931 following a regional meteorological conference convened in Hong Kong in 1930; No. 2 obsolete 1935; No. 3 dormant from 1935 and re-adopted 1956; No. 4 defined for typhoons posing no local danger and never applicable here.
documented Hoisting ended in 2002. Typhoon Lekima in 2001 was the last cyclone for which signals were physically raised; Severe Tropical Storm Kammuri in 2002 was the first for which they were merely issued. The Observatory’s own verb changed with the practice, from 懸掛 to hoist to 發出 to issue. The public’s did not: Hong Kong still calls the warning 風球, the wind ball, and still speaks of hanging and dropping it — a name that has outlived its object by more than twenty years.
documented The rainstorm colours followed an administrative failure. On 8 May 1992 the Observatory recorded 109.9 mm in one hour and five people died; the Education Department did not announce school closures until 11 a.m., so children travelled to schools already shut. The colour system exists so that the closure is decided by the signal rather than by a department.
traditional What prompted the first numbered system in 1917. Systems of this kind are normally rewritten after a disaster, and Hong Kong had catastrophic typhoons in 1906 and 1937, but the Institute could not tie the 1917 revision to a named event in the sources consulted.