The Hanoi Drainage System Monitoring Centre said rain was expected on several consecutive days from August 17 to 25, with daily totals of 20-50 mm forecast from August 18 to 21.
Authorities have been instructed to regulate reservoirs, operate pumping stations, clear drainage channels and deploy teams to areas vulnerable to flooding.
The city's civil defence authorities have asked all 126 wards and communes to closely monitor forecasts for heavy rain, flooding, flash floods and landslides and keep residents informed of potential risks.
Local authorities must inspect riverside and low-lying areas and places vulnerable to deep flooding or landslides, with evacuation plans ready where necessary.
Personnel must also be deployed to restrict access and direct traffic at flooded crossings, areas with strong currents and locations at risk of landslides.
Drainage capacity expanded
Alongside immediate preparations, Hanoi is expanding its drainage and water-storage capacity through a series of emergency infrastructure projects.
Ten projects launched in the first phase had largely completed their main components by the end of June, according to the city's Department of Construction.
Five projects have been completed, including the Me Tri and Yen Nghia 2 retention lakes and drainage upgrades along Thang Long Boulevard and in major urban areas.
Four others have completed their main components, while work on the lower Kim Nguu channel linking the To Lich River to Yen So Pumping Station is nearing completion.
The projects are being integrated into the city's drainage network and have already helped reduce flooding in areas including West West Lake, Nam Thang Long and Ciputra.
The city has ordered the remaining five first-phase projects to be completed in August, except work on La Khe Canal, which is due by September.
Two second-phase projects, Chem and Lien Mac 1 retention lakes, are scheduled to begin construction in August and be completed in the fourth quarter.
More sensors for real-time flood monitoring
Hanoi is also expanding its use of real-time data to manage flooding, with nearly 100 water-level sensors and flood-monitoring cameras already installed.
The city plans to install another 200-300 water-level sensors, cameras and flow meters to track flooding and drainage conditions in real time.
Data on rainfall, water levels, flows and flooding will be used to prepare area-specific response plans, regulate reservoirs, operate pumping stations and deploy personnel ahead of heavy rain.
Forecasts will also help authorities manage retention lakes by lowering water levels before heavy rain and maintaining spare storage capacity for subsequent downpours.
Hanoi aims to comprehensively address persistent localised flooding during the 2027 rainy season by integrating retention lakes, pumping stations, drains, canals, water-storage areas and operational data into a unified system.