Record-breaking Tropical Cyclone Freddy crosses Indian Ocean

By Djordje Gencic, Ivan Smiljanic, Jochen Kerkmann, HansPeter Roseli, Ben Loveday, Hayley Evers-King, Rosmorduc Vinca and Carla Barroso

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. 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 — Litanne in 1994 and Leon–Eline and Hudah in 2000.

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

True Color RGB Cloud Phase RGB

 

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

Freddy made landfall in Madagascar on 21 February, after which it traversed the Mozambique Channel, making further landfall in southern Mozambique on 24 February. It then spent a few days slowly moving over land and weakened into a tropical depression on 1 March (see Tropical Airmass RGB loop of this period in Figure 11).

Throughout the first five days of March, a system returned back over the Mozambique Channel, and once again emerged as a tropical cyclone approaching, and almost making another landfall in, southern Madagascar.

While intensifying, clear ripples in high-level cirrus cloudiness surrounding the cyclone could be seen. These are gravity waves, that are produced by the resonating motion — a consequence of the interaction of strong upward motion that is occurring in the eye-surrounding parts of the cyclone and the tropopause, acting as a limiting boundary for ascent (as visible in the IR 10.8um loop in Figure 12).

From 6 March onwards, the storm made its final leg of journey towards northwest, making a second landfall in Mozambique on 11 March (as it can be seen in Tropical Airmass RGB loop in Figure 13, as well as in high-resolution MODIS Natural Color RGB from the moments before landfall in Figure 14), and finally dissipating on 15 March.

Additionally, the complete Enhanced IR 10.8um loop of the whole life of Freddy can be seen in Figure 15, as well as the total cyclone path in Figure 16.

Freddy the only known tropical cyclone to achieve four separate rapid intensification cycles. The World Meteorological Organization is setting up an expert committee to evaluate whether tropical cyclone Freddy has broken the record as the longest-lasting tropical cyclone on record. It was a named tropical cyclone for 38 days, crossed the entire South Indian Ocean and travelled more than 9,000 kilometres in total. The accumulated cyclone energy (index used to measure the energy released by a tropical cyclone) is the equivalent of an average full North Atlantic hurricane season. During its lifetime, Freddy caused almost 700 fatalities, and almost 1.7 million people were affected across Mauritius, Madagascar, Reunion, Mozambique, Malawi, and Zimbabwe. Some Mozambique locations saw rainfall totals of up 670mm (out of which 300-400mm happened in 48 hours) which caused widespread flooding and landslides across the country.

Additional content

Disaster Charter activation for Tropical Cyclone Freddy in Madagascar
Ensemble Tropical Rainfall Potential (eTRaP)
Tropical Cyclone Freddy may set new record (WMO)
Freddy Delivers Another Blow (NASA Earth Observatory)

This case study is a contribution to the United Nations Ocean Decade