November 15, 2025 | 08:36 pm
TEMPO.CO, Jakarta - Tropical storm formations, which have the potential to develop into tropical cyclones, have been detected south of the Indonesian archipelago. While only one storm was present last Friday, the number increased to two on Saturday, November 15, 2025.
These systems are identified as 97S, which formed south of Bali and Nusa Tenggara, and 98S, a newer development located southwest of Banten. "Based on seasonal prediction data, 97S is expected to continue to intensify," stated Erma Yulihastin, a climate and atmospheric researcher at the National Research and Innovation Agency (BRIN), on Saturday.
According to Erma, the current development of 97S is similar to the formation process of Tropical Cyclone Seroja in 2021, which caused the deaths of at least 181 people in East Nusa Tenggara (NTT) due to catastrophic rainfall.
Erma indicated that one of the key factors supporting the growth of 97S in the coming days is the warming of the Banda Sea, which creates a persistent low-pressure center. The sea surface temperature anomaly in that area is measured at 0.9 degrees Celsius, making it the highest (warmest) anomaly among the waters in and around Indonesia. Erma expressed skepticism that the tropical storm would move south toward Australia, as the sea surface temperature there is relatively normal; instead, she believes it could be easily drawn northward.
If 97S maintains its strength due to these supporting factors, Erma forecasts it could potentially become a cyclone seed, with a high likelihood of a fully formed tropical cyclone occurring within the first ten days of December. "The region nearest to that path is NTT. The region should be on high alert," she cautioned.
The preconditions for 97S to mature into a tropical cyclone include not only the continuously warming sea surface anomaly but also strong wind shear resulting from the interaction between the Madden-Julian Oscillation and Rossby atmospheric waves. Furthermore, the storm is receiving a supply of westerly winds drawn from 98S.
Erma explained that the immediate impact of the current tropical storm is triggering an atmospheric imbalance. Its effects are already being felt through increased rainfall reaching East Java and Central Java. The impact on West Java, according to the climatology professor, is concentrated in the southern region.
If the tropical storm successfully intensifies into a tropical cyclone, its primary impact zone is predicted to shift specifically to the NTT region and its surroundings.
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