Here’s one for David Shukman

I was listening to a 30 second science-bite about hurricanes from David Shukman on the BBC News website yesterday. David was presenting a ‘idiots guide’ to just how hurricanes are formed, and for once the explanation didn’t involve that ‘fast moving ribbon of air high in the atmosphere that the experts call the jet stream’. The basic premise of his explanation was that when a thunderstorm forms over the ocean in the tropics, if derives its energy from the warm seas, and if the temperature of that sea was 26°C or higher, and you added a little bit of rotation, then before you know it you would have yourself a tropical cyclone. Of course this was a thinly disguised bit of propaganda to implant in the viewer’s mind the undisputed fact that: higher sea surface temperatures mean more hurricanes, and of course it must logically follow that’s why they’ve been so many this year. 

Figure 1 – Why are they so many hurricanes? – Courtesy of the BBC

That got me to thinking about El Niño and La Niña events and how they might influence tropical cyclone development in the eastern Pacific. If you apply the same ‘Shukman’ type logic, the extra warmth of the Pacific during El Niño years, should be apparent in the accumulated cyclone energy. So I have produced a couple of graphs that plot ACE for the eastern Pacific from 1950 for both total ACE and ACE anomalies (fig 2). The pale pink and blue stripes in the lower graph are the ENSO events during that time.

Figure 2 – HURDAT2 data from the NHC

I could do further statistical analysis on the results, but I think I wouldn’t find a strong correlation between SST and the ACE index. Active years do occur in El Niño years that’s true, but they also seem to occur just in La Niña or neutral years. I personally think that the BBC should be explaining that although the warmth of the oceans is a key part in tropical cyclone development, any perceived increase in their number and ferocity is a little more complicated, rather than this glib thirty-second news item with its fancy graphics implies.


Addendum

I did find an analysis concerning El Niño and intense tropical cyclones in the Journal Nature but was unable to download it without getting a second mortgage on the house. I did find this online debate about the conclusion that the report came up with which might be of interest.

New Scientist: Thunderstorms triggered by exhaust from cargo ships

Weather buoy 42060

Figure 1 – Courtesy of NOAA & NDBC

I am always impressed when a weather buoy survives an encounter with a hurricane as did 42060 yesterday with category 5 hurricane Maria. 42060 reported mean winds of 64.1 knots (74 mph) with gusts to 81.6 knots (94 mph) at 1510 UTC yesterday (19 September) afternoon, with a minimum pressure of 955 hPa at that time (fig 1). Looking at the wind directions reported by the buoy it looked like the eye of Maria passed close by to the northeast of 42060. Although the AWS was undamaged and still reporting, 42060 According to NOAA, has now broken a drift from her sea anchors (fig 2). I still can’t understand why the same reliable AWS that are used on these weather buoys aren’t used on land stations?

Figure 2 – Courtesy of NOAA & NDBC

 

So why has September 2017 been so cool?

So why have temperatures in the first half of September 2017 been so cool across most of northwest Europe? One glance at the mean pressure chart for the first 16 days will give you the answer (fig 1). The Azores high has been +5 hPa stronger than average, and the Icelandic low has become elongated eastward, with pressure 10 hPa lower than average across the northern Isles. This has resulted in a strong west northwesterly flow across the central Atlantic across much of central Europe. I’m sure that the fast-moving ribbon of air which some people call the jet stream has something to do with it, I find that it usually does.

Figure 1 – Data courtesy of NCEP reanalysis

Here are the fine details of how the circulation has been behaving over the last couple of years with the help of some values from the objective LWT analysis (fig 2). I’ve highlighted September to show how strong and persistent the combined SW-W-NW theme has been this month.

Figure 2

It’s quite noticeable, that from the from the third week in July, maximum temperatures in the CET series have generally been rather flat and slightly below average (fig 3). If you look at the spells bar chart (the fifth chart down) there have been few if any prolonged warm or cold spells longer than 3 days or more with anomalies 2°C either above or below the long-term average, compared with previous summers.

Figure 3 – Courtesy of NCEP reanalysis

Looking over a much larger area with the 12 UTC mean temperature anomalies for the first 16 days of September, you can see that the increased westerly flow has resulted in a large -3°C temperature anomalies across central Europe, and even higher +5°C warm anomalies over northeast Turkey (fig 4).

Figure 4

What about the coming Autumn and Winter?

What does all this portend for the coming Autumn and Winter? I have got absolutely no idea. But if this kind of strong anomalous west or northwesterly flow continue like it’s been doing, I would guess that it looks likely to be cold, windy and rather wintry at times.

Hurricane Maria now close to weather buoy 42060

Figure 1

I see that Hurricane Maria is now getting very close to weather buoy 42060 at 12 UTC, it will be interesting to see just how the buoy gets on. Judging by the wind direction at 12 UTC, the hurricane is not far to the E’SE of the buoys position.

Hurricane Maria: ‘we have lost all’ says Dominica prime minister

Figure 1

The latest news of Maria is that the eye has passed directly over Dominica overnight and has caused widespread devastation. The Guardian has live updates going if you want to keep up with the latest on Maria and even more tragic news from the Caribbean. It’s reminded the world, that in Summer the islands of the Caribbean resemble a coconut shy, as each successive tropical cyclone that forms of Cape Verde tries to knock them of their perch.

As usual, apologies for the contouring in the 06 UTC plotted chart (fig 1), it can’t begin to capture the intense gradients of category five Hurricane Maria, which at the moment has a minimum central pressure of 934 hPa and winds of 140 knots, even with a the addition of a bogus observation. The next island in Maria’s sights according to the NHC, is Puerto Rico in less than 36 hours time.

Hints of an easterly by start of next week

Figure 1

I realise International Science Fiction Day is still a few months away, but the latest few runs of the GFS model have built a large anticyclone over Scandinavia by early next week, at the start of what could be a run of easterlies across the UK. It also keeps the deep low formed from the remains of Hurricane Jose in mid-Atlantic, and it could be the strong southerlies ahead of this intense low of Friday that helps in the formation of a blocking pattern.

Last nights forecast minima from the BBC

Figure 1 – Courtesy of the BBC and Twitter

I find it almost impossible to access a BBC weather forecast from the previous day on the BBC iPlayer. If I wasn’t such a trusting person, I would say that it’s to prevent people like me reminding them of a poor forecast. It’s similar in a way to the reluctance of the Met Office to archive the warnings that they issue, presumably this is to prevent any possible future litigation against them. It seems that the BBC presenters accepted the minimum temperatures from the model for Sunday night, even after it got things wrong on Saturday night for the very same reason, too much wind and cloud, particularly in eastern regions. I wonder if in the state-of-the-art graphics engine that MeteoGroup are poised to introduce will allow the presenter to edit these values?

The forecast temperature extremes across the UK are quite important to the Met Office, they are used at a selected number of places as a metric to calculate their annual bonus. If I remember correctly, they get full marks in verification if the forecast is within +/- 2°C of the actual value. Presumably, they will now use the temperatures that they publicise in their National video forecast, rather than the one that will eventually be provided by MeteoGroup for the BBC, from whatever model they choose to use.

What exactly is going on with the BBC’s weather service?

Its been over a year now since MeteoGroup won the bidding process to take over the running of the Weather forecast on BBC radio and television. In August 2016, Nigel Charters, a project director at the BBC promised that these services would ‘hit your screens, from mobile to television, in Spring next year’ (fig 1). Well, Spring has gone, and so has summer, and now we’re in ‘meteorological’ Autumn, but we are still stuck with the same old BBC graphics, and not the state-of-the-art graphics system as promised by MeteoGroup, and as far as I can see we are still using forecast model data supplied by the Met Office.

Figure 1 – Courtesy of the BBC

So what’s gone wrong?

It’s impossible to say with any certainty, because the BBC and MeteoGroup are both keeping schtum about:-

  • What the new graphics will look like.
  • When the new graphics will start.
  • Who exactly will provide the ‘multiple sources of meteorological data’ (see (2) in fig 1).

If you take a look at the MeteoGroup website they have remained tight-lipped about the whole subject since the news that they had been awarded the contract (fig 2).

Figure 2 – Courtesy of MeteoGroup

Graphics System

MeteoGroup seem keen to get started with their own graphics system, which I understand is not an in-house solution, but one that they buy in from WeatherscapeXT from MetraWeather in New Zealand, although I am not even 100% certain about that. As far as I know MetraWeather provides the current graphics system that the BBC have been using for the past 10 years or more. If that’s so, I can’t see that the slowness in switching is down to the new graphics system itself, but more likely to do with the sourcing of the model data that it uses, and what exactly the visualisation of that data will look like, in particularly the mapping. I hope that we have seen the end of 3D fly throughs, which pardon the pun, never really took off in my opinion.

Forecast model Data

MeteoGroup promise ‘better weather forecasts and solutions’, which to me is the most interesting feature of this whole debacle. If they are not going to use UKMO data, and as far as I know can’t use the ECMWF model commercially, that would just leave the ubiquitous American GFS model. I suppose it’s not outside the realm of possibility that MeteoGroup could decide to buy in some cut-price model data in a deal with the French or Germans. The strengths of the various models was recently put to the test in the Caribbean, forecasting the tracks of hurricane Harvey and Irma, some models perform much better than others. The GFS is primarily built to serve North America, and unlike the UKMO model is not tweaked for an island in the eastern Atlantic. So what happens in the future if the GFS model fails to deepen a low as markedly as the UKMO model does, and on the strength of which, the Met Office issue Amber alerts for storm force winds?

So has anything actually happened?

Well, I suppose that all the weather presenters are now no longer working for the Met Office but the BBC, and some of the old lags have been replaced by women presenters to balance the male-female ratio. I did write back in April that the takeover was imminent, and I suppose that it has happened. But rather awkwardly both for the BBC and MeteoGroup nothing visually has changed, if anything the Met Office have come out of this rather well even if they did lose the contract, their recent national weather video service that’s produced using their new VisualEyes graphics system, which they push out on their website and over social media is rather good.

Next week’s developments in the Atlantic

Another interesting week in the Atlantic coming up.  The GEFS model takes the long-lasting hurricane Jose (1)  finally northward, and just skirting the east of the American eastern seaboard (fig 1). Of the two new tropical storms that have recently formed, Lee and Maria (3), it looks like Lee will perish but Maria is forecast to flourish into a category four hurricane by Wednesday. Maria looks likely to follow a similar track to that of Jose, but maybe come a little further west and cause more problems to the Lesser Antilles, before turning northward as Jose did (fig 1). Further north in the Atlantic, the warm air associated with the remnants of Jose looks like it may trigger the formation of a major extratropical cyclone in the central Atlantic by next weekend (3). This is probably science fiction, but the T+156 from the latest GFS run has an intense low of 959 hPa at 60° north and 21° west by Saturday (fig 2). This

Figure 2 – Courtesy of OGIMET

If this does come about, the southwesterlies ahead of this intense low, could pump up some warm air across the British Isles for the first time this month.

Figure 3 – Courtesy of wxcharts.eu