BMKG Monitors Tropical Cyclone ARNAB and Issues New Warning
Jakarta, CNBC Indonesia — Indonesia’s Meteorology, Climatology and Geophysics Agency (BMKG) has warned of the potential formation of a new cyclonic circulation that could affect weather conditions in parts of Indonesia.
BMKG is currently monitoring the development of Tropical Cyclone ARNAB in the Bay of Bengal. Acting Deputy for Meteorology Andri Ramdhani said the cyclone developed from cyclonic system 98B in the Andaman Sea, which has had a weak circulation since 19 October 2026.
“Based on analysis as of 07:00 WIB on 27 October 2026, the system was at 15.9°N and 86.0°E, with maximum wind speeds of 65 knots (120 km/h) and a minimum air pressure of 985 hPa. The cyclone is moving away from Indonesia and beyond the Jakarta Tropical Cyclone Warning Centre’s monitoring area,” Andri said in a statement on Tuesday (27 October 2026).
“Over the next 24 hours, Tropical Cyclone ARNAB is forecast to move north-west towards a position around 16.2°N and 82.8°E, with its intensity potentially increasing to maximum wind speeds of 70 knots,” he added.
Andri said the system is forecast to weaken over the next 48 hours as it moves over land in India, near 18.5°N and 81.5°E.
Over the next 72 hours, it is expected to weaken further into a Tropical Low near 22.0°N and 81.49°E.
“As the system moves further away from Indonesia, Tropical Cyclone ARNAB is not expected to have a significant impact on weather or sea conditions in Indonesia, including northern Sumatra,” he said.
New cyclonic circulation
Andri also cautioned that a new cyclonic circulation could form near the Andaman Sea from 27 October 2026, although the likelihood of it strengthening over the next 24 hours remains low, according to BMKG weather modelling.
“Over the next two to three days, the cyclonic circulation near the Andaman Sea could develop and move west-north-west, further away from Indonesia,” Andri said.
“The circulation could support the formation of a convergence zone, increasing the chance of rain in parts of Aceh. The system’s development and potential weather impacts will continue to be monitored using the latest analysis of atmospheric dynamics,” he said.
Andri said BMKG would continue monitoring the circulation near the Andaman Sea over the next one to two days through integrated analysis of observational data, satellite imagery and atmospheric dynamics.
The circulation could create a convergence zone that supports the growth of convective clouds and raises the likelihood of moderate to heavy rain in parts of northern Sumatra.
“If there are significant developments that could affect Indonesia, BMKG will issue updates through its official channels. The public is advised to remain calm and follow weather information and early warnings through BMKG’s official website, the InfoBMKG app and its social media account, @infobmkg,” Andri said.
Rainfall potential for the week of 27 October–2 November 2026
In its Weekly Rainfall Potential analysis, released on 26 October 2026, BMKG said that during the first ten-day period of November 2026, 77.72% of Indonesia is forecast to receive moderate rainfall (50–150 mm per ten-day period). Low rainfall (0–50 mm) is forecast for 20.72% of the country, while high rainfall (150–300 mm) is expected across 1.56%. Moderate rainfall is predicted to prevail across most of Sumatra, Kalimantan and Papua, as well as parts of Java and Sulawesi.
Low rainfall is still expected in parts of Lampung, Banten and Jakarta, along Java’s northern coast, in East Java, Bali and the Nusa Tenggara islands, and in parts of Sulawesi and Maluku.
“Although rainfall is generally forecast to be in the low-to-moderate categories, a number of atmospheric dynamics could still increase rain-cloud formation across various parts of Indonesia,” BMKG said.
“Over the coming week, the Madden–Julian Oscillation (MJO) is forecast to affect most of western and southern Indonesia. Equatorial Rossby waves and Mixed Rossby–Gravity waves are also expected across parts of western Indonesia, while Kelvin waves are forecast to be active in parts of northern Indonesia. The combined activity of the MJO and atmospheric waves could increase cloud growth, particularly in areas with concentrated air masses and unstable atmospheric conditions,” BMKG added.
BMKG said that, in addition to the MJO and atmospheric waves, cyclonic circulations expected to form in the Andaman Sea and in the Pacific Ocean north of Southwest Papua could also affect regional wind patterns. Both systems could create areas of slowing and converging winds around their centres. This could promote convective cloud growth and lead to moderate to heavy rain, potentially accompanied by lightning and strong winds.
“Therefore, even though ten-day rainfall totals are generally expected to remain in the low-to-moderate categories in several areas, significant daily rainfall remains a risk because of interactions between regional and local atmospheric dynamics,” BMKG said.