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The Met Office chart sequence below shows the development of cyclone Gerard, starting out (on these charts) as a warm front wave over Newfoundland early on 14th, crossing the Atlantic as an innocuous looking frontal wave feature, then deepening explosively by 37mb/24h up to 06UTC 16th, or 15mb/6h to 00UTC 15th. The former value exceeds by some margin the definition of explosive development (24mb/24h at 50N) whilst the latter ranks highly alongside other famous windstorms (see graph below). Peak intensity was reached over the western part of the English Channel. Extreme winds hit western France (ref 00UTC 16th chart below), and also western Normandy including the Cotentin Peninsular (ref 06UTC 16th chart below). There were suggestions of a sting jet (unconfirmed) which, based on the structure and evolution of fronts and mslp on these charts, would have most likely affected northern and western Brittany and western Normandy.
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16th |
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Met Office analysis charts for 14th - 16th January 2023.
Context of max 6h deepening of Gerard (vertical back line) versus other 'famous' windstorms (From Hewson and Neu, Tellus, 2015). We don't of course have, for Gerard, the ERA-Interim equivalent max deepening rate shown on the y-axis.
The plots below show HRES analyses of MSLP and 6 hour rainfall from 14 January 00UTC to 18 January 00UTC, every 12th hour.
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