Tropical Storm Chalane
Severe Tropical Storm Chalane was the first of three consecutive tropical cyclones that struck Mozambique in the 2020-21 South-West Indian Ocean cyclone season. As the fourth tropical depression, third named storm, and second severe tropical storm of the season, Chalane developed out of a zone of disturbed weather which was first monitored RSMC La Réunion on 19 December. Despite conditions slowly becoming unfavorable, the system formed into a tropical depression on 23 December due to the presence of a Kelvin wave and an equatorial Rossby wave, as well as warm sea surface temperatures. The depression soon strengthened into Tropical Storm Chalane on the following day. Chalane made landfall on Madagascar on 26 December and weakened, before emerging into the Mozambique Channel a couple days later. Subsequently, Chalane restrengthened, before making landfall on Mozambique on 30 December. The system weakened as it moved inland, degenerating into a remnant low later that day. However, Chalane's remnants continued moving westward for another several days, emerging into the South Atlantic on 3 January, before dissipating later that day.
As Chalane strengthened, the coordinating of emergency supplies began in Madagascar, Mozambique, and Zimbabwe, and the Joint Typhoon Warning Center issued a Tropical Cyclone Formation Alert. Late December 26, Chalane made landfall in Madagascar, causing flooding. But overall, there was little damage. Chalane was downgraded to a tropical depression as it passed through Madagascar. On 30 December, Chalane, now a Severe Tropical Storm, made impact on Mozambique, several institutions were damaged, but Chalane made less damage than expected. The same day, Chalane made landfall in Zimbabwe, before downgrading to a remnant low. The remnant has been causing some rainfall in neighboring countries. Overall, 7 people died in Mozambique and the damage was $134,000.
Meteorological history
On 19 December, RSMC La Réunion began monitoring a zone of disturbed weather situated approximately southwest of Diego Garcia. The system was located in a favorable environment for intensification due to the presence of a Kelvin wave and an equatorial Rossby wave, as well as warm sea surface temperatures. Chalane experienced low to moderate vertical wind shear and a good upper-level outflow. Conditions began to deteriorate over the next several days as the system meandered to the west, however the storm managed to reach tropical depression status on 23 December as northerly wind-shear began to affect the storm causing most of the thunderstorm activity and winds to be localized to the south of the center. Approximately a day later at 06:00 UTC 24 December, the depression strengthened to Moderate Tropical Storm Chalane as a scatterometer pass revealed gale-force winds on the southern side of the highly asymmetric wind field. Since the storm was becoming aligned with the subtropical ridge, Chalane began to strengthen, with winds reaching as wind shear decreased. Around the same time, the Joint Typhoon Warning Center issued a Tropical Cyclone Formation Alert. At 21:00 UTC that day, the JTWC designated Chalane as Tropical Storm 07S.However, Chalane continued to struggle from the effects of strong north-northeasterly wind shear. Chalane passed just to the south of Tromelin Island on 25 December where a pressure reading of was recorded, indicating Chalane had likely weakened while also displaying a deteriorating cloud pattern, therefore Chalane was downgraded back to tropical depression status on 18:00 UTC that day. Slowly, Chalane continued westward towards the Malagasy coastline as a tropical depression. Convective activity remained disorganized while the center accelerated west up to landfall on 26 December at 18:00 UTC in Mahavelona, Madagascar. Chalane degenerated into a surface trough shortly afterwards on 27 December, although its center still remained intact. MFR ceased advisories at this time, as re-intensification was uncertain. Chalane made its passage over Madagascar over the remainder of the day, before emerging over the Mozambique Channel on 28 December, where advisories resumed and Chalane re-developed into a tropical depression. Six hours later, Chalane reintensified into a moderate tropical storm yet again, with the development of a curved band. Chalane continued to strengthen with a central dense overcast bundled with the curved band becoming apparent on satellite imagery Chalane gained severe tropical storm status at 06:00 UTC on 29 December with the formation of an eyewall. Chalane continued to slowly gain strength while in its favorable environment, gaining peak strength 12 hours later with maximum sustained winds of and a pressure of. Shortly after peaking, Chalane made landfall north of Beira, Mozambique on 30 December and became subject to weakening. Chalane degenerated into a remnant low later that day over Zimbabwe, as all thunderstorm activity had ceased, and the MRF issued their final advisory on the storm. However, Chalane's remnants continued westward over the next several days, emerging into the South Atlantic on 3 January, before dissipating shortly afterward.