CARE2022 Hong Kong Conference

44 I: Warnings and Emergencies • Warnings and response for rainstorms and heat HKO uses the well-established territory-wide Amber/Red/ Black warnings for rainstorm. Probabilistic forecast of heavy rain for the next day is under trial by HKO with some government departments internally. While there have been requests for higher granularity of the rainstorm warnings, it should be noted that rainstorm warnings at the district level, for example, will invariably lead to higher false alarm rates which, given the present technologies, are beyond the public’s tolerance, and thus such possibilities are only being explored with specialised users. During the hot spells in 2022, HKO launched the prolonged heat push messages associated with the very hot weather warnings for the public. To further raise public awareness, two levels for the very hot weather warning is being considered. FIGURE 5.1 Probabilistic approach for heavy rain forecasting Source: HKO FIGURE 5.2 Enhancement of very hot weather warning services Source: HKO Special alert on prolonged heat starting from July 2022 Explore further enhancement on the Very Hot Weather Warning Coordinate closely with related government B/Ds on necessary revision of guidelines Year No. of days with maximum temperature ≥ 33ºC at HKO No. of days with maximum temperature ≥ 35ºC at HKO 2017 29 1 2018 36 5 2019 33 2 2020 47 3 2021 54 4 2022 52 15 Grand ensemble of multiple numerical weather prediction models Probability of Heavy Rain 28 2022 SEPT HIGH Category Definition High ~70% chance of heavy rain Medium ~50% chance of heavy rain Medium Low ~25% chance of heavy rain Low <5% chance of heavy rain Trial of a potential new service on a trial with various government bureaux and departments 5 Preparedness and Resilience