Tight Gradient Between Ex-Leslie & Azores High To Bring ‘Stormy’ Weather To UK Late Week (Includes Video!)

Written by on September 10, 2012 in United Kingdom & Ireland with 0 Comments

Image off Charles DarwinBeagle Diary

It’s been a pretty remarkable hurricane season this year when you think that there’s been a significant struggle for any tropical storm to organise and become a hurricane within the traditional breeding grounds. Joe Bastardi has alluded to this frequently on this. Each system has fought near constant dry air and or shear and Leslie has been no exception. The dry air, shear and even upwelling has meant that Leslie spinning on the spot day after day has looked very unimpressive and rather shabby.

Now that the system is moving and north after doing very little on Bermuda. It will get away from those cool, upwelled waters and should intensify into a Category 1 hurricane once again as she sets her sights on Atlantic Canada. A front sweeping off the US coast is causing excelleration in Leslie’s forward speed and this will increase dramatically as she gets further and further north.

NCEP GFS surface/precip chart courtesy of WeatherBELL Models

The reason Leslie is expected to be a Cat 1 storm even at Newfoundland’s latitude is due to the fact that there will be a window of oppertunity over the next 36 hours with waters well above normal as well as a warmer than normal Gulf Stream. The eventual forward speed (likely to top 30-40 mph), combined with much higher than normal heat content means that Leslie likely runs out of time to weaken before striking eastern Newfoundland with the Avalon likely to be impacted the most.

This storm could pack quite a punch, not only because it should support Cat 1 intensity with winds sustained at between 75-80 mph but factoring in higher gusts likely with a fast moving system means impacts can be worse.

Flooding is also likely going to be high on the impact list as well as intense winds.

Leslie will undergo two types of intensification over the next 3 days

Later tomorrow is when Leslie is expected to impact Newfoundland and will rapidly push out into the North Atlantic where it will make that transition into an extra-tropical system. I expect it to either be making that transition as it speeds across eastern Nflnd or as it moves away simply because the shear will have greatly increased and waters will be cold here. There will also be a thermal contrast between warm air to the south and cold air to the north with this system riding along the boundary (jet stream) and so the warm core is lost and a fully cold core develops, so baroclinic properties kick in as this system pushes NE towards the southern tip of Greenland and then shoots due east towards southern Iceland. This is where Ex-Leslie deepens for a second time in her life, thanks to warmth surging north from the mid-Atlantic ridge and frigid air flowing south off Greenland. Pressure should drop into the mid-970s, a very different type of deepening from what is expected to occur within a very different environment between Bermuda and the Canadian Maritimes over the next 24 hours.

Check out the below GFS surface chart for Wednesday. Notice it has a 978 mb storm near Greenland. Amazing to think that system is what will strike eastern Canada tomorrow as a potential hurricane and it will take barely a day to have travelled nearly 1,000 miles. Just shows you how fast the air above our heads travels doesn’t it.

NCEP GFS surface/precip chart courtesy of WeatherBELL Models


So what could Leslie mean for us here in the UK late week?

What’s interesting for us here in the UK, especially Scotland and northern England as well as Northern Ireland is that while Leslie may be nothing more than a classic low taking aim at Iceland with no lower pressure than what we’ve seen in storm centres all summer, it’s the fact that we’re going to have a pretty strong Azores high building north towards the UK at the same time ex-Leslie tracks across or just south of Iceland by as early as Thursday.

A tightening of the pressure field means we may get some very strong west winds here and depending upon just how close the centre of circulation gets, the tighter the pressure field between the low sub-980 low and strong 1028 high pressure will be. Keep in mind that we still have leaved trees and so damage is possible with this scenario.

We certainly keep a close watch on this situation in coming days.

NCEP GFS surface/precip chart courtesy of WeatherBELL Models

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