Rare and Dangerous Movement of Tropical Cyclone Senyar Over Sumatra Island

Indonesia is no longer safe from the path of tropical cyclones. The emergence of tropical cyclone seed 95B in the Malacca Strait since November 21, 2025, has triggered extreme weather and disasters such as floods and landslides in the regions of Aceh and North Sumatra. Greater disasters are likely to occur as this low-pressure system strengthens into a tropical cyclone.

The cyclone seed that has now developed into Tropical Cyclone Senyar is currently moving towards the coast of Aceh. For the next few days, this tropical cyclone is predicted to move over the land areas of Aceh and North Sumatra.

The report from the National Disaster Management Agency (BNPB) indicates that floods and landslides struck four districts in North Sumatra Province, namely Sibolga, North Tapanuli, Central Tapanuli, and South Tapanuli on Monday (24/11/2025) and Tuesday (25/11/2025). This disaster has resulted in the deaths of eight individuals, 58 injuries, and thousands of people displaced.

Heavy rain has also triggered alerts in seven sub-districts in North Aceh Regency. The local government has declared a state of emergency through the North Aceh Regent's Decree Number 360/845/2025 regarding the Declaration of a State of Emergency in North Aceh for the year 2025, effective from November 23, 2025, to January 15, 2026.

The threat of disaster occurring in the northern part of Sumatra Island has intensified after the 95B cyclone seed developed into a cyclone. "Based on atmospheric analysis as of November 26, 2025, at 07:00 WIB, the system (95B) has undergone intensification and is officially classified as Tropical Cyclone Senyar, which is currently monitored in the waters of the eastern Malacca Strait off Aceh," said the Head of the Meteorology, Climatology, and Geophysics Agency, Teuku Faisal Fathani, on Wednesday.

BMKG's analysis indicates that the tropical cyclone Senyar is currently centered around 5 degrees North latitude and 98 degrees East longitude, with a minimum air pressure at the center reaching approximately 998 hPa. The maximum wind speed around the system can reach up to 43 knots (80 km/h). Over the past 6 hours, this cyclone has been moving westward towards the land area of Aceh at a speed of about 10 km/h, triggering an increase in the growth of convective clouds in the surrounding area.

The impact of the system on weather conditions in Aceh and North Sumatra is predicted to be significant, with the potential for very heavy to extreme rainfall accompanied by strong winds. The rain clouds that are forming are increasingly influenced by the supply of water vapor in the warm waters of the Malacca Strait, as well as the increase in wind convergence in the northern part of Sumatra.

"In the next 6 hours, tropical cyclone Senyar is predicted to continue moving closer to the coast of Aceh and has the possibility of making landfall," said Fathani.

The Director of Meteorology at the Meteorology, Climatology, and Geophysics Agency (BMKG), Andri Ramdhani, is concerned that the movement of the tropical cyclone Senyar will have a significant impact on the increased threat of disasters as it crosses land. As is common, the emergence of a tropical cyclone will trigger heavy rainfall in the surrounding areas it traverses.

"Based on monitoring of BMKG AWS (Automatic Water Station) data, as of Wednesday (26/11/2025) early this morning at 03.00 WIB, several locations in Aceh have experienced extreme rain, with an intensity of over 150 mm per day," said Andri.

In the next 6-24 hours, this cyclone is expected to continue moving towards the west-southwest. After interacting with land, the system is predicted to gradually weaken.

However, extreme weather remains a potential occurrence as a subsequent impact and may trigger hydrometeorological disasters such as floods, flash floods, and landslides in the regions of Aceh, North Sumatra, Riau Islands, Riau, West Sumatra, and surrounding areas in the next 2-3 days.

BMKG climate researcher Siswanto stated that this tropical cyclone is a rare phenomenon as it crosses the land of Indonesia. "This (tropical cyclone Senyar) is a rare phenomenon, but it is not the only tropical system that has ever affected this region," said Siswanto.

According to him, in 2001, Tropical Cyclone Vamei emerged, triggering floods and landslides in Singapore, Malaysia, and Indonesia. Subsequently, Tropical Cyclone Viyaru also occurred in 2013, resulting in extreme rainfall in Aceh and North Sumatra.

"Compared to other tropical cyclones around Sumatra, Cyclone Senyar has a weaker intensity but remains significant due to its path crossing over land across northern Sumatra," said Siswanto.

According to the laws of nature, Indonesia should be safe from the path of tropical cyclones. Cyclones are influenced by the Coriolis effect, named after its originator, the French mathematician Gaspard Gustave de Coriolis. The Coriolis effect causes any object moving on this continuously rotating planet to turn to the right or clockwise in the northern hemisphere and to the left or counterclockwise in the southern hemisphere.

The Coriolis effect weakens in value, even approaching zero, as one gets closer to the equator. This results in the absence of the Coriolis effect at the equator itself, and in the theory of atmospheric fluid dynamics, there will be no twisting effect on wind movement, such as cyclones at the equator.

Ocean conditions at that time were relatively warm, higher than the climatological average, thus providing latent energy for the growth of tropical systems.

Due to the Coriolis effect, tropical cyclones generally form at high latitudes, above 10 degrees. On the other hand, tropical cyclones derive their energy from the evaporation of large amounts of water from the ocean surface, which releases heat and creates convection or rising air. This only occurs in warm waters, with a minimum sea surface temperature of 26 degrees Celsius down to a depth of 50 meters.

Based on this parameter, the central sources of tropical cyclone formation are usually in the warmer equatorial edge zones compared to the surrounding waters and then move to higher latitudes, either south or north. This results in several countries, such as the Philippines, Taiwan, Japan, or Vietnam, frequently experiencing the passage of tropical cyclones. Meanwhile, Indonesia tends to be safe from their passage.

Nevertheless, the emergence of Senyar and previously Vamei indicates that the northern region of Sumatra is also at risk of being traversed by tropical cyclones. Previously, Indonesia was also affected by Cyclone Seroja in April 2021, which triggered devastation in East Nusa Tenggara.

The warming of ocean waters serves as fuel that increases the risk of tropical cyclone formation near the Indonesian mainland. Siswanto stated that the formation of a tropical cyclone in the Malacca Strait in November 2025 was also caused by sea conditions that were warmer than normal.

"Sea surface temperatures (SST) around 29–30 degrees Celsius in the Malacca Strait support deep convection and the strengthening of tropical systems. The sea conditions at that time were relatively warm, higher than the climatological average, thus providing latent energy for the growth of tropical systems," said Siswanto.

When compared to several tropical cyclones that have developed in the region of Indonesia, tropical cyclone Senyar is different because its path crosses the land of Sumatra, rather than only affecting from the sea. Cyclones Vamei (2001) and Viyaru (2013), and now Senyar, demonstrate that tropical systems can form or approach at low latitudes near Sumatra, although this is rare.

"Historically, the trend of sea surface temperatures in the Malacca Strait has shown a gradual increase since the early 1980s, in line with global warming and the influence of regional climate variability," said Siswanto.

With this trend of rising ocean temperatures, Indonesia, which was previously considered relatively safe from the direct threats of tropical cyclones, is now at greater risk.