Why is it raining in Saigon? Because it’s the rainy season. Sure, but if you want to be more specific, you can cite conditions in the Bay of Bengal, more than 2,500 kilometers away. It’s there that the wind conditions form that flow across the Gulf of Thailand, sucking up the moisture that drenches Vietnam’s southern metropolis.
Any Saigoneers who have been caught in a downpour long for a way to know the precise times storms will start and stop. Photo by Alberto Prieto.
Such insight about where “the bullet is loaded” for the storms that strike Saigon comes from Del Elson, the Australian man behind the Saigon Weather Facebook page and recently launched Instagram account. The long-awaited answer to Hanoi’s Weatherdude, Del has spent the past several years sharing charts that detail wind speeds and directions along with expected rainfall and interpretations of what effect they will have on the city. While Vietnamese speakers have some choices, such as Đài Khí tượng Thuỷ văn Nam Bộ (Southern Vietnam Meteorological and Hydrological Station), Saigon Weather has emerged as a go-to place for anglophone followers to get answers to what Del says they most want to know: “Is my laundry going to get wet? Do I need to pack an umbrella?”
Visuals that Del shares on Saigon Weather's social media.
With Saigon’s relatively stable year-round temperatures, residents may not be in the habit of checking weather reports. But, particularly during the rainy season and for those in neighborhoods prone to flooding, there is a need for reliable predictions about downpours and tidal levels, especially when phone apps frequently prove inaccurate. Del fills this niche while also offering some fascinating details about weather for science nerds.
Del is himself one such nerd. A mathematician by training and software engineer by occupation, his interest in weather developed naturally. Born and raised near Sydney Harbor, like many of his peers, he grew up sailing. Major yacht races would begin with weather reports, including the opinion of a local expert, which instilled in him a trust and admiration for those able to advise on future wind and rain. After graduating from university in Western Australia, Del returned to the Sydney area where he continued to sail, even purchasing his own boat and joining a local yacht club he described as “a drinking club with a sailing problem.”
Del aboard his boat. Photo via Del Elson
During these years of sailing in Australia, the financial company he worked for outsourced a project to Vietnam, where he met his future wife, a fellow engineer. Before they got engaged, she even joined him for a portion of the year he spent on a sailboat at sea. During those months on the ocean, Del’s safety depended on accessing and understanding weather data. Once he moved to Vietnam to get married and start a family, that ability to turn data points regarding wind speed and direction, surface barometric pressure, and rainfall into reliable guesses about weather conditions proved useful. He explained: “I got more into looking at the local weather forecasts because sometimes when you're in a city, you need to know where it's going to rain tomorrow. And for a city where the weather is very much governed by the monsoon winds, you wouldn’t think it would be that hard to predict the weather.” It wasn’t long until he launched the Saigon Weather page to share his predictions with anyone who might be interested.
Enough of a community of followers has now developed that Del recently held an in-person presentation. He stunned attendees, Saigoneer included, with the fact that monsoons aren’t, in fact, periods of heavy rainfall, but rather heavy winds. It just so happens that the winds often bring with them downpours. And perhaps even more astounding: it's not accurate to say Saigon has two seasons (wet and dry) but rather three. From May through October, Saigon experiences the southwest monsoon, which leaves the city hot and wet, while November through April is the northeast monsoon, which brings cool, dry air. Less known, however, is the southeast monsoon. Not occurring every year and arriving during random months — sometimes April, sometimes November — it brings short, sudden rainstorms in the mid-morning.
A slide Del shared during a presentation to reinforce typhoon's inability to hit Saigon.
Even more shocking than knowing you’ve gotten the number of seasons wrong would be thinking Saigon is at risk of typhoons. It is not. Tropical cyclones are unable to cross the equator, and Saigon is close enough to be protected by the latitudinal safety band. So if you ever see a report suggesting a typhoon is coming up from Singapore, you know not to trust it. Such fake news is occasionally spread online, and sharing it now puts people in danger of government punishment.
Within this atmosphere of pervasive misinformation, Del shares basic, straightforward prognostications: where it might rain, how much, and when, as well as what areas might flood. Ascertaining such seemingly simple information requires synthesizing a massive amount of data produced by weather models that compare current conditions with historical records to make predictions. Complicating the process is that the foremost inference engines are operated by the US, Canada, and Europe, and optimized for temperate latitudes. This means they are less effective for tropical areas, like Vietnam, where wind behaves differently. Thankfully, the models can be supplemented with information provided by weather scientists in Brunei, Singapore, Fiji, and Hong Kong. Doing so allows Del to make localized predictions, something major weather apps do not, which is why whatever your phone says is dubious at best.
An example of a climate model produced by the United State's NOAA via Climate.gov.
Even more problematic than applying weather models designed for cool climates in equatorial locations is a recent degradation of reliable data due to climate change. To have enough historic understanding to base guesses on, “you need like 10 years of good data, usable good data, and it's questionable at the moment,” Del explained. Unfortunately, amidst warming seas and erratic winds, past patterns no longer portend what will happen today, making meteorologists around the world less accurate than before.
In addition to good data, to best predict weather, one needs a high-powered computer. Such processing power filled entire rooms just a few years ago, but can now fit on a tabletop. Unfortunately, that hardware is also valued by AI practitioners, and crypto-miners before them. A desire to churn out videos of people posing in an '80s aesthetic or rapping cats is now driving the cost of such devices upwards of US$16,000. Still, Del plans to purchase one soon, which will allow him to run full models as opposed to piecing together information from select data sets.
Left: Previous computing hardware needed to run weather models. Photo via Commonwealth Scientific and Industrial Research Organisation.
Right: Hardware required today. Photo via NVIDIANews.
By running these models, as well as looking at the local tide charts put out by the local port service, Del will be able to post daily reports. And in the meantime, he will continue analyzing portions of the larger data sets for updates several times a week, work which is already proving helpful. A local astronomy club relies on his information to know which nights will be clear enough for stargazing. Some Saigon cricket clubs also consult him about when they should start their games to ensure they are done before it starts to pour.
A soggy Saigoneer is an unhappy Saigoneer. Photo by Alberto Prieto.
On my way to meet for a coffee with Del, perhaps ironically, it started pouring. As we both sat in the moderately damp state one finds themselves in every September, I asked if he knew it was going to rain. “I did,” he said with a big grin. This ability to remain in good spirits amidst the unavoidable realities of weather seems central to his approach. When asked what we can expect for the rest of the year, he noted that the coming dry season will bring drought to the Mekong Delta; record high temperatures to Saigon in the spring and probably a late start to next year’s wet season. Or as he put it: “A lack of swimming opportunities for boofheads in Bùi Viện.”
