Eye of Storm Eowyn will settle over Caithness at noon with some ‘quirky’ effects, predicts local weather watcher
A local weather pundit predicts that the centre of Storm Eowyn is expected to pass over Caithness around noon today with some “quirky” effects you may notice.
Wick weather watcher Keith Banks describes the benign impact of the exceptionally low pressure that will be associated with storm Eowyn as “quirky”.
”At midday, Eowyn should be sitting slap bang over Caithness and Sutherland,” reports Keith.
“Even by North Atlantic winter storm standards, Storm Eowyn is a true behemoth and classified as an extratropical depression by meteorologists.”
He pointed out some unusual effects brought on by the storm as the pressure drops to a possible low of 945mb. “That's very low indeed for an Atlantic depression, even during the winter.
“Setting aside the impacts, and they will be severe, a benign consequence of the very low atmospheric pressure will mean that you can have a cuppa quicker than is usual on Friday.
“This is because the boiling point of water at lunchtime and the early part of Friday afternoon will be a couple of degrees Celsius lower than usual. If the pressure gets down to 945mb then kettles will boil at 98.0C instead of the usual 100C. Average pressure at sea level called the MSLP is 1013mb.
“Crucially, bubbles can form inside the liquid only when the pressure just exceeds the pressure exerted by the atmosphere. The liquid is now said to be 'boiling'.
”When the atmospheric pressure is below normal, boiling will occur at a lower temperature. Mean sea level pressures MSLPs below 950mb over the UK are unusual events. Wick's lowest MSLP is currently 942.6mb recorded on December 20, 1982.
He noted that the British Isles record lowest MSLP is currently 925.6mbar recorded in Crieff, Perthshire on January 26, 1884 but that Storm Eowyn will not challenge the record.
“On December 24, 2013 Storm Dirk had a central pressure of 927.0mb as it passed close to NW Scotland. On this date the pressure in Wick bottomed out at 944.6mbar. On January 3, 1984 the town witnessed a MSLP of 943.6mb.”
The deepest North Atlantic depression on record had a central pressure of 912mb-915mb as it passed the south of Iceland on January 10, 1993.
“Eowyn underwent an extraordinary explosive cyclogenesis as it was catapulted across the Atlantic with its central pressure falling by a remarkable 51mbar in 24 hours-more than double the rate to satisfy the established criterion for the phenomenon of explosive cyclogenesis.
“Extratropical winter depressions like Eowyn typically form along sharply demarcated boundaries that can develop between high and low atmospheric temperatures. Displacement of the warm sub-tropical air creates a low-pressure centre that is subsequently propelled north-eastwards across the Atlantic by a powerful 'zonal' jet stream.
“Jet stream velocities above the NE Atlantic are currently in excess of 250mph. Prominent 'jet streaks' embedded within the jet stream core will readily facilitate the development of further vigorous depressions in the wake of Storm Eowyn.
“Further intensification of so-called 'weather bombs' are fuelled by feedbacks from air temperature and humidity gradients and associated violent winds and precipitation.
“In the case of Storm Eowyn a plunge of cold dry air from the stratosphere called a 'sting jet' will enhance deepening and cause winds to gust in excess of 100mph across western parts of Eire, Ulster and possibly the most exposed regions of the west of Scotland.
“In Caithness, the initial impacts will occur during the breakfast to late morning period when east-south-easterly winds will increase to mean velocities of gale force 8 perhaps severe gale force 9 at times, gusting up to storm 10 to violent storm 11 before veering southerly and moderating as the centre moves across Caithness.
“However, a more violent spell of wind is likely to develop across Caithness and other parts of the far north during the late evening and continue into the early hours of Saturday after Eowyn moves away to the north of the Orkney Isles towards Norway.
“When this happens west-south-west to westerly winds are likely to increase again to a sustained gale force 8 or even severe gale force 9, with violent and destructive gusts in the violent storm 11 and hurricane force 12 categories probable. The gusts may reach 80mph in exposed locations.”
Keith says that the aforementioned factors coupled with a sharp contrast in temperatures and moisture at the ocean's surface have created optimal conditions for Storm Eowyn to have the potential to become one of the “most notorious and dangerous storms” to have affected the British Isles.
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