Atlantic update/St. Jude Storm

Possible paths for the St. Jude storm of 2013.  (Met Office by way of the Telegraph)

Possible paths for the St. Jude storm of 2013. (Met Office by way of the Telegraph)

Note that I didn’t even use the word “tropical.” Lorenzo is long gone, and the GFS just isn’t showing anything in the next several days.

However, a storm doesn’t have to be tropical to cause damage, and the entire southern region of the UK is getting set for a big one. They’ve already christened it the St. Jude Storm (because its hurricane-force winds will arrive on that saint’s feast day). Some forecasters say that it could be as bad as one in 1987 that killed 13 people, while others believe that a storm in 1990 that killed 47 people and caused a lot of damage might be a more appropriate comparison.

This storm hasn’t formed from an Atlantic hurricane (there haven’t been any in the right position).  Rather, say meteorologists, it’s the result of a very low-pressure Atlantic extratropical cyclone combined with two strong low pressure systems that originated over North America.

Will update below as things develop. Good luck, UK, and stay safe tomorrow!

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Current infrared imagery of St. Jude Storm.  (Met Office)  Click to enlarge.

Current infrared imagery of St. Jude Storm. (Met Office) Click to enlarge.

October 27, 12:13 a.m. Eastern: Here is the Met Office’s weather observations page. The vectors are tightly clustered and difficult to sort out, but by just randomly picking sites, I’ve found a low wind speed of 3 mph in Waterford City, Eire (pressure 989.9) and, so far, a high of 40 mph on The Cairnwell in the Eastern Highlands. That’s at 3000 feet, but Aberdaron in Wales has an elevation of only about 300 feet, and it’s currently experiencing 39-mph winds, per this chart. Also, here is the satellite imagery page in IR (because it’s dark there now). You can switch the view over to visible at any time.

Here is a page with recent buoy data. A ship in the area of station 64045, waaaay off the northwestern coast of Scotland, has reported a wind speed of 31 knots (36 mph) and wave heights of almost 28 feet…however, the other ships in that general vicinity report lower wind speeds and wave heights.

People generally react to data like this in a polarized way – they’re bored to tears, or else they’re addicted. I fall in that latter group, but won’t post more details for the sake of readers in the former group.

October 27, 12:11 p.m. Eastern: Here’s a news update, including a note that “[t]he intense low pressure system is expected to begin pummeling parts of Britain’s exposed coast from late Sunday local time, before strengthening overnight and into Monday morning.”

Just a few general bits of information gleaned from the various sites: The winds are already in the 40-mph range along parts of the southern and western coast, per current posts on this Met Office map, including winds of 44 mph at Chichester, gusting to 50 mph, and also 44 mph in Wales at Mumbles Head (wind gusts 61 mph) and Pembrey Sands Samos (57 mph gusts). Wave heights at Pembroke Buoy range from 5.9 to 22 feet.

Here is the current satellite imagery (visible, not infrared) at the Met Office page.

Such storms are seldom as visually striking as full-blown tropical cyclones, but they're dangerous, nonetheless.

Such storms are seldom as visually striking as full-blown tropical cyclones, but they’re dangerous, nonetheless.

Best tweet at this moment:

Some webcams:

Dawlish Sea Wall on the Exeter-Penzance line. (Live, with text updates here.)

Langland, Wales/Oystermouth (Still image, ? hourly)

Exmouth Seafront. (Live)

Update, October 27, 2:53 p.m. Eastern: I think the center of low pressure is between the Scottish coast and the Faroe Islands. The K7 buoy in that general area is reporting a respectable 970.7 mb (28.66 inches).

So why are the strongest winds expected in coastal southern Britain and not northern Scotland? Because air moves from an area of high pressure towards a low-pressure area. Air movement is just another way of saying “the wind.”

The steeper that pressure gradient, the faster the winds blow, increasing sort of like water speed increases when it goes from flowing in a plain to flowing down a very steep slope.

This means that right now, given that low pressure off coast of northern Scotland, the higher pressure should be far to the south, sandwiching coastal/southern Britain in between. And indeed, a quick look shows that pressure near the Gascone buoy in the Bay of Biscay is 1012.7.

I just picked that point randomly; it’s not necessarily the highest pressure point currently. However, a pressure difference of 42 mb seems very respectable to me!

So, why isn’t the entire island getting blasted, south to north? I suspect friction from contact with the land surface has a lot to do with that. It slows part of an air parcel down, which tends to break it up. The wind speeds above the ground and over England and Scotland are probably quite fast, but the lower levels in contact with the ground are much slower.

I experienced this effect first-hand, by the way, in 2005, when I was living in West Central Alabama. Hurricane Katrina hit the Louisiana coast and came straight for us, causing a lot of damage along the way. The damage did lessen as the storm weakened during its overland journey, and by the time it got to us, it was a high-end tropical storm/low-end Category 1 (still very unpleasant and damaging, but in an extreme thunderstorm/wind storm way, not as a major calamity).


Update October 28, 11:03 a.m. Eastern:
Things are calming down for Britain, where three people have died and there is much damage and transportation disruption, but the storm continues over Europe, where it’s called Christian. Here is more information. The European Severe Weather Database also has a graphic of selected data here.

Here is a look (without a legend, unfortunately) at current weather warnings in Europe:

At least 35,000 homes are reportedly without power in Brittany and Normandy, France.

Update, October 29, 9:48 Eastern: Per this news report, 6 people died in Germany, 5 in Britain, 1 in the Netherlands and 1 in Denmark, with 1 woman lost in France after being swept out to sea. This storm caused massive transportation and power disruption, as well as a lot of damage along its path.

So…even though the tropical Atlantic has been very quiet this year, its overall stormy character still comes through occasionally, loud and clear.



Categories: Weather

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