Former Hurricane Lorenzo is now “Storm Lorenzo,” named by the Irish Meteorological Service as the powerful tempest approaches. Winds as high as 80 mph, localized flooding and travel disruptions are all anticipated as the post-tropical cyclone gets set to make landfall in Europe.
With forward speeds topping 45 mph, Storm Lorenzo is cruising — enough so that the worst of the weather will only occur over a 9 to 12 hour period. For Ireland, the roughest was expected from dinner time on Thursday overnight into early Friday morning.
A 63 mph wind gust was measured by an offshore weather buoy 300 miles west of Ireland situated over Northeast Atlantic’s Rockall Trough. Air pressure at that buoy dropped to 28.63 inches — down from more than 30 inches — indicating how efficiently the storm is evacuating air upward and outward. That powerful drop in air pressure creates a vacuum effect, drawing in air from all around and spurring the strong winds associated with Storm Lorenzo. That air pressure is commensurate with what’s seen in many Category 2 hurricanes.
Orange wind warnings are plastered over the western half of Ireland; on the leeward side, it’s a less severe yellow warning. Conditions should subside significantly by noon local time Friday.
In the tropics, the strongest hurricanes often are the ones that exhibit the greatest symmetry. That’s because there are no strong temperature gradients to jumble up their structure. But once storms move to the mid-latitudes, becoming extratropical or post-tropical cyclones, strong contrasts between warm and cool air masses help storms to grow fronts, with the system transitioning from symmetrical to more of a large comma-shape. That was evident Thursday morning on satellite imagery.
It should be noted that, as a result, the strongest winds may not coincide with the bulk of the rain. Radar from Ireland showed an initial swath of rain passing by Thursday morning, followed by a dry slot and associated clearing. However, as the low center draws even nearer, those winds will continue to climb.
That dry slot is also important in the formation of a narrow jet of strong winds at the tip of the comma’s wraparound. This occurs when cloud and precipitation matter is blown into the dry slot, undergoes evaporative cooling, descends and brings those roaring upper-level winds down to the lower atmosphere or even the surface. One surefire way to detect a potential “sting jet” in the making is to search satellite imagery for a scorpionlike stinger, possibly composed of smaller banded cloud wedges, at the apex of the comma. If one develops, it could bring localized wind gusts well over 80 mph to a narrow path near the surface.
That’s unlikely right now, but still not out of the question.
As Lorenzo crosses the Irish Sea overnight Thursday, it will weaken some, though still affecting Britain with sustained winds up to 50 mph and gusts of 55 to 65 mph in exposed locations, per the British Met Office.
The agency wrote that “some delays to road, rail, air and ferry transport are likely” in Northern Ireland, where a yellow warning for wind is in effect. That risk on Friday shifts to the extreme southern Britain, mainly over Wales and the South West.
About a quarter of all flights into and out of Dublin Airport were delayed or canceled as of Thursday morning, but that could change as the storm draws nearer.
Ireland and Britain are no stranger to being visited by post-tropical hurricanes. Seven ex-hurricanes have passed near or over Ireland in the past 25 years. Only one system — Debbie in 1961 — made an Irish landfall while still in hurricane form.