Erma Yulihastin, a researcher at the National Research and Innovation Agency’s (BRIN) Center for Climate and Atmosphere, warned on Monday that residents of Greater Jakarta, particularly those living in Banten’s Tangerang regency, should be wary of “extreme rain” and “heavy storms” on Wednesday.

These storms, according to Erma, would originate at sea but would move inland driven by westerly winds and the cross-equatorial northerly surge (CENS).

“As such, Banten [province] and Jakarta [and its satellite city of] Bekasi will be the central locations where the storms will strike, starting from noon until evening on Dec. 28, 2022,” Erma wrote on her Twitter account. She added that heavy rain was likely to spread to other areas in West Java.

The Meteorology, Climatology and Geophysics Agency (BMKG) refuted Erma’s claims of “heavy storms” but said that the Greater Jakarta area remained at risk from extreme weather in the coming days.

“The terminology for storm, more or less means a tropical cyclone [that must include] strong winds that cause heavy rain. [A potential for storms] has been detected in the northern part of Papua,” Dwikorita told a press conference on Tuesday.

“When we are talking about extreme rain, it does not have to be a storm […] The trend for extreme rain has been on the rise since Dec. 21, and will continue to do so until Dec. 29,” she said, referring to a similar warning for extreme weather issued by the BMKG on Dec. 21.

Like Erma, Dwikorita cited the CENS as a factor behind the potential for extreme weather in the coming days. Dwikorita also pointed to the Asian monsoon season as well as the flow of cold air from the Asian continent, particularly Tibet, heading toward the equator, as other contributing factors.

To this end, she said that all six provinces in Java – Jakarta, Banten, West Java, Central Java, East Java and Yogyakarta – and a number of other provinces in the country, including Bali, West Nusa Tenggara (NTB) and Papua, were prone to extreme weather on Tuesday and Wednesday.

According to a warning posted by the BMKG on its Twitter account, all of Jakarta’s districts were expected to experience light to moderate rain from 10 a.m. until 7 p.m.

More extreme weather

The BMKG also said that there was a high potential for more extreme weather until at least Jan. 2. All of Java’s provinces, along with Bali, East Nusa Tenggara (NTT) and NTB were likely to experience heavy or very heavy rainfall over the time period.

Meanwhile, 11 other provinces across the country, including Aceh, West Sumatra, South Kalimantan, South Sulawesi and Papua, are likely to experience moderate to heavy rainfall until Jan. 2.

Along with the heavy rainfall, the BMKG also said that a number of coastal areas were at risk of high waves. The Natuna Sea in Riau province and the southern shores of NTT, for instance, were likely to experience waves reaching up to 6 meters in height.

Meanwhile, the southern shores of Java, stretching from Banten all the way to East Java, as well as the southern shores of Bali and NTB, are likely to experience waves between 4 and 6 meters in height.

As a result, the BMKG has instructed people living in coastal regions to brace for tidal flooding, with 21 provinces, including also Jakarta, thought to be at a particularly high risk.

Weather modification

With Jakarta and neighboring West Java on high alert for heavy rains and flooding, National Disaster Mitigation Agency (BNPB) head Suharyanto told a press briefing on Tuesday that authorities would “employ weather-modification technology” to mitigate the risks of hydrological disasters, particularly amid the high public mobility during the year-end holidays.

When asked by reporters at the same briefing as to how the Jakarta administration would keep people safe during extreme weather events, acting Jakarta governor Heru Budi Hartono advised private companies to allow their employees to work from home.

Dwikorita of the BMKG urged regional administrations to ensure that their water-management infrastructure, such as dams, was ready to anticipate potential floods, coastal flooding and high waves.

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