Record-breaking Tropical Cyclone Freddy crosses Indian Ocean
5 February 2023 00:00 UTC-24 February 08:00 UTC
Long-lived tropical cyclone Freddy traversed more than 9,000km across the entire southern Indian Ocean in 17 days, starting on 5 February from the seas north of Australia, making landfall in Madagascar on 21 February.
27 February 2023
22 February 2023
By Djordje Gencic, Ivan Smiljanic, Jochen Kerkmann, HansPeter Roseli, Ben Loveday, Hayley Evers-King, Rosmorduc Vinca and Carla Barroso
This long journey makes Freddy one of 5 in known history to set a record for track length in the southern Indian Ocean, noting that Freddy actually formed further east than the previous cyclones.
Tropical cyclone Freddy developed in the Timor Sea, and was reported by the Australian Bureau of Meteorology (BOM) on 5 February. What followed was a 17-day westward journey through quite favourable atmospheric conditions, conducive to tropical cyclone strengthening and development. This system underwent a few intensity changes during its travel to the west, and at its strongest was a category 5 equivalent cyclone on the Saffir-Simpson scale, with sustained winds of 270km/h, while during significant portions of time it maintained category 3+. On 21 February, at around 16:15 UTC, Freddy made landfall on the southeastern coast of Madagascar.
This whole journey has been captured in three particularly long loops of the IR 10.8µm (Figure 1), the Tropical Airmass RGB (Figure 2) and the Enhanced IR 10.8µm (Figure 3), where the development phases can be easily tracked.
Regular IR 10.8µm in grey scale shows the cloud tops surrounding the eye of the cyclone as bright white. Additional information on the cloud top temperature can be obtained by enhancing the colours in the coldest part of the spectrum, as in the Enhanced IR 10.8µm loop. The tropical version of the Airmass RGB is specially tuned for low latitudes and tropical regions, to account for particularly high water vapour content, and can be used to monitor jet streams and dry/wet air masses in the mid- and upper troposphere, which significantly impact tropical cyclones.
It is widely-known that for the development and life-cycle of a tropical cyclone the underlying sea temperature must be at least 26-27C. Sea Surface Temperature (SST), as estimated with Sentinel-3 SLSTR Level-2 product, is displayed in Figure 4 (note that the product can only be derived over cloud-free areas). A simple sample of SST was done for a location along the anticipated track of the cyclone and the measurement showed 28.88C, above the threshold mentioned.
Figure 5 shows a comparison of the Suomi-NPP VIIRS True Color RGB (left) and Cloud Phase RGB (right). It is important to note that while the True Color RGB offers a realistic, true colour view of what would be seen from the satellite, the Cloud Phase RGB reveals much more in cloud type and microphysics (pink or white = low/water clouds, cyan or blue = high/ice clouds) and, consequently, quite clearly shows the cyclone eye. While the True Color RGB shows various, quite similar, shades of grey/white surrounding the eye, the Cloud Phase RGB displays the low clouds of the eye in pink, and the surrounding strong cumulonimbus wall as bright blue. Both of these composites will be available with Meteosat Third Generation's FCI.
Comparison of SNPP images
Figure 5: Comparison between the SNPP VIIRS True Color RGB and Cloud Phase RGB, 19 February
On 21 February, Metop-B's ASCAT product, from the OSI SAF, estimated winds up to 32.17m/s (115km/h) while the cyclone was approaching Madagascar (Figure 6). Note: ASCAT winds saturate at around 30-35 m/s, the real winds were much stronger.
Freddy made landfall at around 16:15 UTC on the east Madagascar coast, near the town of Mananjary (Figure 7).
The Tropical Airmass RGB loop of Freddy landing is shown in Figure 8.
Freddy had a notable effect on the wave field in the southern Indian Ocean, as shown in the significant wave height (SWH) measured by the Copernicus Sentinel-3 SRAL and Sentinel-6 Michael Freilich Poseidon-4 altimeters (Figure 9).
Hindcast and forecast models from the Copernicus Marine Service ingest this altimetry data, alongside information from multiple other sources, and show that the effect of the storm on the sea surface is relatively localised, but results in SWH of over 7m near the storm centre. These waves are driven westward onto the Madagascan coast (Figure 10).
Relevance to ocean challenges, and further resources
As part of the United Nations Ocean Decade, ten specific challenges are being addressed. This work, and the data underlying it, support Challenge 6 - Increase community resilience to ocean hazards. Estimates of significant wave height and wind speed, derived from the sea surface topography missions, are an essential input into the forecasting systems that allow us to provide early warnings to coastal populations.
To support the UN Ocean Decade this case study has an accompanying marine Jupyter Notebook, which revisits the narrative and replicates some of the altimetry animations you see here. You can find this notebook in our ocean case studies repository, which you are free to clone for your own use or to support your own training. Alternatively, you can launch the notebook directly on Binder.
Further progression
After hitting Madagascar, Freddy continued westwards, re-strengthened over the Mozambique Channel and made landfall over Mozambique, as a tropical storm (Figure 11).
Additional content
Disaster Charter activation for Tropical Cyclone Freddy in Madagascar
Ensemble Tropical Rainfall Potential (eTRaP)
This case study is a contribution to the United Nations Ocean Decade
