Cyclone Belna

Map plotting the storm's track and intensity, according to the Saffir–Simpson scale

Map key

Saffir–Simpson scale

  Tropical depression (≤38 mph, ≤62 km/h)
  Tropical storm (39–73 mph, 63–118 km/h)
  Category 1 (74–95 mph, 119–153 km/h)
  Category 2 (96–110 mph, 154–177 km/h)
  Category 3 (111–129 mph, 178–208 km/h)
  Category 4 (130–156 mph, 209–251 km/h)
  Category 5 (≥157 mph, ≥252 km/h)
  Unknown

Storm type

Tropical cyclone

Subtropical cyclone

Extratropical cyclone, remnant low, tropical disturbance, or monsoon depression

Three simultaneously active cyclones in the North and South-West Indian Ocean. From top left to right: Pawan, Belna, and Ambali

MFR began highlighting the potential for tropical cyclone development in their daily bulletins on 25 November, noting an increase in shower activity west of Seychelles.[3] Aided by the passage of a Kelvin wave and a favourable window in the Madden–Julian oscillation, a broad trough of low pressure began to take shape within the storm activity, extending across the equator.[4][5] Projections from computer models remained in disagreement over the system's future, complicated by the concurrent development of a tropical disturbance in the northwestern Indian Ocean along the same trough.[5] A loosely-defined wind circulation was detected 263 km (163 mi) south of Mahe, Seychelles on 29 November, offset from convection.[6] Over the following days, this circulation tightened within an environment moderately conducive for tropical development.[7][8] Météo-France declared the system as a zone of disturbed weather on 2 December; at the time the system had drifted west from its point of origin.[9] Although the storm was better organised and the environment conducive for intensification, the storm's wind field initially remained elongated and rainfall remained north of the storm's centre.[10][11][12] The disturbance became a tropical depression on 5 December, attended by an increase in rainbands and the return of convection at the centre of circulation;[13][14] at 18:00 UTC that day, the system was upgraded to Moderate Tropical Storm Belna.[9]

Belna was upgraded to severe tropical storm status early on 6 December.[9] Around the same time, a cloud-obscured eye briefly became apparent in microwave satellite imagery. Due to a strengthening area of high pressure to its east, Belna began to curve from its initial westward drift to a more directed southwestward trajectory.[15] After a brief period of strengthening,[9] Belna's central dense overcast remained largely unchanged throughout 6 December before signs of resumed intensification emerged by the day's end, followed by the development of another eye 9–19 km (5.6–11.8 mi) across.[16][17][18] With the storm's eye becoming better defined, MFR upgraded Belna to a tropical cyclone early on 7 December. Hot towers were detected atop and within the storm's radius of maximum winds, suggesting the onset of a more accelerated rate of intensification.[19] However, the presence of dry air in the mid-levels of the troposphere towards the storm's southeastern quadrant prevented Belna from developing considerably.[20] At 18:00 UTC on 7 December, Belna's winds topped out at 155 km/h (95 mph) before fluctuating at a slightly lower strength over the ensuing day.[9] The system's structure disorganised significantly in a short period, caused by both the dry air and northerly wind shear.[21]

The cyclone's structure varied considerably throughout 8 December, at times featuring a small eye surrounded by intense lightning activity and at other times degrading in response to an intrusion of dry air into the Belna's circulation.[22][23] Belna's strength was highly variable in part due to its small size, making it susceptible to changes in the local atmospheric environment and complicating forecasts.[24] On 9 December, a new phase of intensification began as Belna approached the Madagascar coast near Soalala, with an eye becoming apparent on visible satellite imagery.[25] In its advisories, the MFR noted a "spectacular intensification spell" in the hours leading up to Belna's landfall on Madagascar, assessing the cyclone's winds at 155 km/h (95 mph) and the pressure at 965 mbar (965 hPa; 28.5 inHg)–the lowest analysed over the course of the storm's existence—as Belna moved ashore at 15:30 UTC on 9 December. The storm then began to weaken as it tracked farther inland, parallelling the western coast of Madagascar.[26] By 12:00 UTC the next day, Belna's winds had tapered below tropical depression thresholds,[9] though the storm retained a well-defined wind circulation with tightly packed rainbands.[27] Belna curved towards the southeast over Madagascar, and deep convection associated with the cyclone dissipated on 11 December.[28][29] MFR issued their last update on the system later that day while the centre was over Haute Matsiatra,[9] while the remnant circulation centre associated with Belna was last noted in MFR's bulletins on 14 December.[30]

• Cyclone Bondo – made landfall near Mahajanga, killing 11
• Cyclone Fame – struck northwestern Madagascar at a similar intensity
• Cyclone Hellen – slow-moving storm that brought flooding rainfall to Mayotte and northwestern Madagascar
• Cyclone Herold
• Tropical cyclones in 2019
• Weather of 2019