About xmetman

An ex-metman passionate about all things to do with weather, climate and clouds

3D Clouds

Figure 1

In the first visible satellite image this morning, you can see how quickly the cold front of Brian has swept eastward overnight, leaving in its wake towering cumulus and cumulonimbus across the south and the west, which almost have a 3D look about them illuminated as they are by the dawn sunshine (fig 1). A lovely spiral of rain across central Ireland marks the position of the storm, with some very potent showers already moving eastward across Wales and the Southwest in the gale force southwesterly (fig 2)

Figure 2

Overnight gusts from Brian

Figure 1

Met Éireann might have a state amber warning in force for gusts to 80 mph, but the highest gusts overnight (as there were with Ophelia on Monday) have been in the southwest of England and the west of Wales, with gusts to 78 mph at the Sevenstones lightvessel and 71 mph at Mumbles head at 06 UTC this morning, both exceeding the 70 mph in the yellow warning issued by the Met Office yesterday. I doubt if the Met Office will update this warning, and are just hoping that the gradient doesn’t tighten anymore and there won’t be anymore gusts over 70 mph.

Brian is a stereotypical low that you get every so often in Autumn and Winter across the British Isles, but the way the threshold of the yellow and amber warnings are pitched means that we get into this situation with almost every low that comes along. Is it yellow or is it amber, which is complicated further with the storm naming. Perhaps if the thresholds were based on mean speeds as well as gust speeds, then a mean speed of 34 knots at a coastal site could be the yellow threshold, and a mean speed of 34 knots (gale force 8 or 39 mph) at an inland site amber? Well it’s just an idea.

Dangerous Brian

Figure 1

Two spiralling extratropical storms in one week as dangerous Brian moves in off the Atlantic. I notice that the pressure at 62095 (‘0’ marks the position of weather buoy 62095 in figure 1, and the inset plot grid in figure 2), which is just to the north of Brian, has started to bottom out at 975.9 hPa, but Brian will continue to deepen to 964 hPa by midnight according to the forecast chart from the Met Office. I notice that the wave height being reported from the weather buoy 62442 at 49° north are already 9.2 metres (30 feet), and the wind there has veered westerly gale force 9.

Figure 2

Storm Brian

Figure 1

Storm Brian was named by Met Éireann yesterday, and reading the news item that the Met Office issued, it looks like if it had been left up to them they wouldn’t have even bothered. As well as naming the storm Brian, Met Éireann have also issued a status amber and yellow wind warning for Saturday for gusts of up to 80 mph (fig 1), and notice that in their warning they specifically mention the expected maximum mean wind speed of 40-50 mph, which makes for a textbook warning as far as I’m concerned (fig 2), and which the Met Office refuse to do.

Figure 2 – Courtesy of Met Eireann

Arguably, the gradient on the latest T+36 from the GFS model is just as tight across the southwest of Wales as it is across Ireland (fig 1), but the Met Office are sitting on their yellow warning, but have enlarged the area (fig 3). This time the Met Office have chosen to use the old 45-55 mph but with 60-70 mph gusts around the coast ploy. I would have thought that there would be gusts to at least 80 mph on the Welsh coast on Saturday, as there were gusts to 90 mph there on Monday when they only had an amber warning for gusts of 80 mph in force.

Why take any chances?

Why not just issue an amber warning for gusts to at least 80 mph for coastal areas, and leave the yellow alert for inland areas?

Half the problem, I’m sure, of why they don’t do this is because of their reliance on hand drawing the various warning areas. If this web interface was improved by the use of a GIS system, they could then much more easily highlight an amber area at regional authority level or even postcode level around the coasts. The finished product would be more accurate, professional and directly tied to the individual grid point wind gusts from the NWP model.

Figure 3 – Courtesy of the Met Office

Whether the wind gusts will reach the yellow or amber threshold (which I guess is 80 mph) depends on when the rapid intensification of Brian occurs, if it’s later, or if it goes on slightly longer the winds will be that much stronger. The Met Office are in no doubt that it’s already underway and by the time the low reaches Ireland it will be already well occluded (fig 4).

Figure 4 – Courtesy of the Met Office

I notice that the process is already well under way at 62095 (fig 5).

Figure 5

Guardian: Ophelia’s arrival hints at a new vulnerability for Europe

My first reaction to this article in the Weatherwatch section of the Guardian was to measure the distance in miles between the Isles of Scilly and the nearest 26°C SST isotherm and then divide by thirty!

Figure 2

And so if the North Atlantic did continue to warm at this rate (with the 26°C SST moving 30 miles every 10 years), you can expect the 26°C SST isotherm to be lapping on the beaches of the Cornish Riviera in a little over 692.7 years in the late summer of 2709!

I do think Paul Brown did manage to completely miss the point with this article about Ophelia though, and instead of repeating the “hurricanes only form over water of 26°C” mantra like we’ve never stopped hearing from the BBC weather presenters of late, the question that he should have been asking was “why did Ophelia intensify to a major category three hurricane over an Ocean with marginal SST of between just 22 and 24°C“?

Tropical cyclones that form close to the Azores [1851-2017]

Figure 1 – HURDAT2 data courtesy of the NHC

I’ve spent sometime writing new code to allow me to rubber-band any area in a map, and plot the tracks of all the tropical cyclones that originated within this area. I did it to confirm what I thought was happening, and that is that most tropical cyclones in the central Atlantic would end up migrating northeastward towards the British Isle. I don’t know why I thought that, and once I got the program working I could see clearly how wrong I was (fig 1). As you can see from the results there is more of a Catherine-wheel effect going on, and if a tropical cyclone does form in that area of the central Atlantic, it seems that it can end up flying off in virtually any direction.

Ophelia is clearly visible as is ex-Hurricane Charley (1992), the other one I notice is ex-tropical storm Grace (2009) which I can’t remember at all, but apparently was at the time the northeastern-most forming Atlantic tropical cyclone on record.

Obviously I was motivated by the recent hurricane Ophelia to investigate where hurricanes that start their lives in the central Atlantic end up, especially where the SST are marginal, as was the case with Ophelia. It does make you appreciate just what an unusual hurricane Ophelia was, because although there have been tropical storms in past years, Ophelia is the first tropical cyclone to have formed in the central Atlantic and to make for the British Isles as a major hurricane.

The application is pretty flexible and as well as allowing you to rubber-band any area of the map with your mouse and find where all the tropical cyclones that originated in a selected area ended up, it also enables you to use in reverse, and what I mean by that is you can use it to find where all the tropical cyclones that terminated in a selected area started from. These are all the hurricanes that terminated over an area of southern Texas and northern Mexico since 1851, it’s a bit cluttered but it does seem to work (fig 2).

Figure 2 – HURDAT2 data courtesy of the NHC

I don’t know if there would be any call for this kind of functionality, but if there is I can now do it! I suppose the next query I should write is to find all tropical cyclones that reported a track point in a selected area. That would be an impossible task using 6 hour track points alone, and you would have to test if a track of a cyclone intersected with a selected area. I would have to be very desperate to take on a piece of coding as sophisticated as that.

Late fog warning from Met Office

Figure 1

A late warning of dense fog for parts of England was issued by the Met Office early this morning. As far as I can see the warning wasn’t issued till 0540 AM when most affected stations, at least in eastern England, had been in fog since midnight. I can’t for the life of me see why this warning wasn’t issued much earlier.

Figure 2 – Courtesy of the Met Office

Saturday advisory from the Met Office

The Met Office have issued a yellow ‘advisory’ warning today for storm Dietrich this coming Saturday. These ‘advisories’ seems to be the way they’ve started doing things these days, which I must say is a vast improvement on last year, when they almost seemed to wait until the last-minute to give the general public a clue about what they were thinking. They’ve chosen to use a brand new ploy in this strong wind warning, the 50-70 mph ploy, and lucky us they even managed to mention the wind direction in this one! Now all that we’ve got to get them to do is to include the maximum mean wind speed that they expect, and we’ll have a proper warning, just like those issued at RAF outstations for the last 70 years. I suspect a big part of the problem is that many Chief Forecasters have never spent any time on an RAF outstation, or ever issued a warning come to that.

Figure 1 – Courtesy of the Met Office

Autumn warmth continues

Figure 1

The current warm spell of weather across Central England, and rather spookily ushered in by the start of the astronomical Autumn, seems to be running on and on, and there doesn’t seem to be any sign in the latest NWP forecast charts that it intends to stop! The above chart clearly shows the warmth of the last four weeks or so (fig 1).  The maximum temperature on ‘Ophelia day’ (the 16th of October) of 19.5°C, broke a record that had stood since the great Autumn of 1959,  no mean feat.

Figure 2

Autumn mild spell continues into start of November

The low pressure area that’s currently over the northeast of Russia; as forecast by the latest run of the GFS model; is set to be replaced by a large anticyclone with a central pressure of 1040 hPa or higher by this time next week. This will in effect stem the flow of cyclones from tracking from the Atlantic across Scandinavia and into Russia as they have been doing of late, as pressure rises over Scandinavia and a block forms. This in turn will back the flow across the eastern Atlantic as it becomes progressively more meridional. This in turn will ensure the continuation of the autumn warm spell, and if anything we could see even higher anomalies both by day and night as we move into Autumn.

There’s quite a bit of conjecture in that last paragraph, so take it with the pinch of salt it deserves, but remember that you read it here first.

Firming up the forecast for Saturday

Figure 1

The forecast for Saturday is starting to firm up now with the latest T+84 products from the UKMO and the GFS. The tightest gradient at 12 UTC on Saturday look to be across south Wales and the Southwest, all though truth be said, it looks a pretty stormy affair anywhere south of 54° north across the British Isles, as the low itself tracks across central Ireland and across the Irish Sea, exiting across the southeast coast of Scotland by midnight.

By the time Dietrich; as I think it will be called by the Berlin Meteorological Institute; reaches the British Isles on Saturday it’s already a well occluded low, because it peaks as early as Friday at 20° west in the central Atlantic, when its central pressure is much lower at 960 hPa. So I suppose if the cyclogenesis took place later than forecast it could arrive in an even more angry mood than this forecast. Don’t you just love the British weather?

And please rest assured as Darren Bett has just reminded us

This IS NOT a hurricane!