Why not hourly weather forecast?

After many "huge" rains caused flooding in Ho Chi Minh City, leaving people unable to react, many people asked why there is no accurate weather forecast on an hourly basis?

Answering this question, Mr. Le Thanh Hai - Deputy General Director of the National Center for Hydro-Meteorology - said that hourly weather forecasting will take a few more years to be implemented because it requires a lot of equipment and human resources.

Heavy rain on the afternoon of September 26 caused severe flooding on Truong Son Street (Tan Binh District, Ho Chi Minh City). People hope to soon receive an accurate rain forecast so they can plan to "save themselves" - Photo: HUU KHOA

There is only a thunderstorm warning bulletin.

Mr. Hai said that currently the meteorological industry only provides bulletins in the form of thunderstorm warnings. In case of thunderstorms occurring half an hour to three hours before, the Southern Hydrometeorological Station (SRH) also issues such warnings on its website and contacts the Ho Chi Minh City Traffic Radio and Television channels to inform the people.

However, with extremely short-term forecasts of weather events occurring in the next 0-12 hours, Ho Chi Minh City is currently building a project with financial support from the World Bank (WB) to have high-resolution models for forecasting.

According to Mr. Hai, to implement short-term forecasts, it is necessary to continuously update and issue forecast bulletins. For example, from 10am, the forecast will be issued from 10am to 5pm (six hours in a row), then at 11am, the overlapping forecast must be continued. Therefore, a lot of human resources are needed in addition to the monitoring system, high-resolution forecasting models...

“Quantitative forecasting (how many millimeters of rain) for tropical regions is very difficult, requiring additional investment in high-resolution radars. If all equipment and technology conditions are met, ultra-short forecasts can still quantify how many millimeters of rain will fall in the next 2-3 hours, with an accuracy of up to 90% with a three-hour or six-hour forecast period,” said Mr. Hai.

Mr. Hai further explained that extremely short-term forecasting must be done continuously throughout the system from monitoring data to the release of the forecast bulletin, and must be done 24/7, even hourly forecasting.

Currently, Hanoi and Ho Chi Minh City have not been able to do this, but only warn about thunderstorms in the following way: when a thunderstorm is detected, they will announce in a few hours which district it will rain in and how many centimeters of flooding it will have, but they have not yet quantified the specific amount of rain in millimeters.

It is difficult to predict rainfall accurately.

Regarding this, Mr. Le Dinh Quyet - Deputy Head of the Southern Hydrometeorological Forecasting Department - said that this station currently conducts weather forecast bulletins in the Southern region as well as Ho Chi Minh City, including 24-hour and 48-hour forecasts, weather trends that may occur in the next few days, and 10-day forecasts...

Some news are sent to VOV traffic news, Ho Chi Minh City Television, posted on the website of the Central Steering Committee for Disaster Prevention and Search and Rescue: www.kttv-nb.org.vn. For dangerous weather news (low pressure, storm), thunderstorm warnings (rain, thunderstorm)... are also sent to the Ho Chi Minh City Steering Committee for Disaster Prevention and Search and Rescue, Vietnam Television...

Mr. Quyet acknowledged that rain is a meteorological element that fluctuates over space and time, so it is difficult to accurately forecast the amount. However, the Central Hydrometeorological Forecasting Center still builds very short bulletins (nowcasting) warning of thunderstorms a few hours in advance to post on the website and send to some units as above. The bulletins are made in the form of "thunderstorm monitoring and warning bulletins".

Mr. Quyet gave an example: from September 26 to 28, the Central Hydrometeorological Forecasting Center continuously broadcast bulletins such as bulletin (No. 1) broadcast at 3:24 p.m. on September 27 with the following content: "Currently, convective clouds are developing in many places in the Southern region. Warning: rain and thunderstorms are occurring and continuing to spread..., Ho Chi Minh City has rainfall of 20 - 40mm". About an hour and a half later, there was bulletin No. 2 with the following content: "Rain and thunderstorms are occurring and continuing to spread in Dong Nai, Binh Duong... In the next 40 minutes, Ho Chi Minh City may have very heavy rain with rainfall of 60 - 80mm".

Meanwhile, according to the City Urban Drainage Company, the largest rainfall on the evening of September 27 (from 5:45 p.m. to 8:45 p.m.) was 95.3 mm (Thu Duc station)...

Commenting on the accuracy of the above news, Mr. Quyet said that some news reports are about 80% accurate, but some are less accurate...

According to TTO