Storm before the Storm: The satellite clues that reveal Cyclone Harry

Storm before the Storm: The satellite clues that reveal Cyclone Harry
Prof. Charles Galdies
Institute of Earth Systems

Information is now available that allows the full analysis of Meteosat SEVIRI Water Vapour imagery at 6.2 μm (WV6.2) between 18 January and 20 January 2026 (12:00 UTC). This satellite channel doesn’t show rain directly but instead patterns in the upper atmosphere (roughly 5 to 12 km up), where much of the steering and intensification of storms happens. The whitish areas mark higher, colder cloud tops and rising air, while dark areas frequently indicate drier air aloft and sinking motion. This is often the fingerprint of strong upper-level atmospheric dynamics.

On 18 January, we can already see a broad atmospheric disturbance over the eastern Atlantic begins to lean toward Europe. Over time it sharpens into an upper-level ‘dip’ in the flow west of Spain. This is important because Mediterranean cyclones often start higher up: the atmosphere first sets up a powerful swirl in the upper levels, and only later does a surface low fully form and intensify.

By 19 January, a striking dark ribbon of dry air pushes toward the western Mediterranean. Meteorologists call this a ‘dry intrusion’. This is like a wedge of descending air that helps tighten the storm’s structure. At the same time, a bright, expanding cloud shield can be seen spreading across the western basin and North Africa, signalling widespread uplift and growing organisation of the weather system.

The clearest triggering moment appears around 19 January 16:45 UTC when the water vapour patterns begin to curl cyclonically, with a developing comma-shaped structure. The storm’s ‘engine room’ is visible in the annotated image below where dry air is wrapping in on one side, moist rising air strengthening on the other. This contrast helps energise the system and supports the severe impacts that we all know about.

This is why atmospheric remote sensing matters. Satellite channels like WV6.2 allow us to watch these dynamics, improving how we diagnose, anticipate, and explain extreme events, especially over the sea where conventional observations are sparse. Atmospheric dynamics and remote sensing are taught as a core element of the BSc Earth Systems course of the Institute of Earth Systems.