Storm Justine hits the Azores

By Ângela Lourenço (IPMA) and Natasa Strelec Mahovic (EUMETSAT)

The Azores, an archipelago in the middle of the north Atlantic, is often affected by extratropical cyclones, frequently deep and intensive ones, with heavy rain, strong winds and high seas.

On 26 January 2021 a low, named Justine by IPMA Azores, started to develop from a frontal wave at the eastern coast of the United States (Figure 1) and moved east-northeast across the Atlantic basin. It was expected to pass close to the Azores western islands later in the day on 28 January.

During the 26th the surface low deepened and developed a rather slow movement, but on 27 and 28 January the storm rapidly intensified below the left exit of the jet stream and started moving faster (Figure 2). The development seen in the loop of Airmass RGB images is typical for the Rapid Cyclogenesis process.

The first forecast track (Figure 3) showed that later on 28 January, Justine could pass over Corvo and Flores islands (the western group of the islands) as a deep cyclone.

Eventually, the cyclone centre passed near Corvo (around 500 km) at 21:00 UTC on the 28th, further west than initially forecast. The main threats were the wind gusts, and IPMA-Azores issued several warnings, including a red wind warning for Corvo and Flores islands. The highest wind gust of 110 km/h was registered on Flores island at 03:00 UTC on the 29th, just after the cold front had passed. Between later in the afternoon of the 28th and early morning of the 29th the wind gusts were between 90 km/h and 110 km/h.

On 27 January, in the early stage, Justine was seen by scatterometer sensors. At 13:30 UTC both ScatSat-1 and ASCAT-A overpassed the low centre (Figure 4) and in the southwest quadrant winds were already 30 to 35 kt.

Later on the same day, at 22:30 UTC Justine's centre was again seen by ScatSat-1 (Figure 5), and the winds were already higher in the southern part of the storm, reaching 35 to 40 kt.

Along with the wind gusts there were also high seas threat that lasted longer and would also affect western Europe (Figure 6).

The storm was forecast to affect north Iberia, and in Guarda, a weather station in central Portugal, 99 km/h wind gusts were registered on 30 January.

On 27 January at 15:00 UTC, both the GOES-16 Airmass RGB and Cloud Phase RGBs (Figure 7) showed the rapid deepening phase of the storm, starting approximately at this time. In the Cloud Phase RGB thick water clouds with small droplets appear yellow, and thick water clouds with large droplets appear pink. Blue shades are related to ice clouds on top of the storm. Convective clouds embedded in the system can be recognised.