Wave Depression Watch 16th/17th November - Low Risk of Intense Storm

Deep Easterly · 13-11-2010 8:37pm #1

Couldn't find an appropriate thread post on regarding this but latest 12z model runs are continuing to show a possible potant wave depression developing and affecting Ireland during the coming mid-week period.

Maquiladora and M.T have already mentioned this possible development in other threads. The ECMWF/UKMO & GFS runs tonight continue to show the potential for a developing wave to the SW of Ireland on monday which may have an impact on Ireland later on.

GFS 12z forecast for next Tues 12:00 UTC:

UKMO 12z forecast for Wed 12:00 UTC:

ECMWF 12z forecast for Wed 12:00 UTC:

All 3 models in agreement regarding this possiblity but postioning of the feature is not. It may well come to nothing closer the time and may bring nothing more than an average wet day over Ireland. Might be worth discussing though for better or worse as there is little else of interest on the weather front at the moment!!

All images c/o Meteocentre

maquiladora · 13-11-2010 9:10pm

Something to keep an eye on alright DE. Models are showing better agreement on this now but I still feel there is a lot of uncertainty with the track and intensity.

Hi-res look at the 12Z ECM :

Centre of the depression at 978 right over Cork. Small core and fairly nice looking isobars. I'm sure that would bring gales to the south/southeast coasts and perhaps further inland depending on how it tracked?

12Z GFS develops it further west, limiting the threat of strong winds to more western/northwestern coasts:

12Z NOGAPS and CMC develop it too but as a slightly weaker system and take it up through the middle of the country.

I agree DE, worth keeping an eye on cause there isnt much else happening! Will probably turn out to be nothing special but that won't stop me dreaming of a re-run of Xmas Eve 97.

Su Campu · 13-11-2010 11:14pm

The NOGAPS develops up to 60kt mean winds with this system off the south on Tuesday, which I'm sure won't happen. The EMCWF, GFS and UKMO are pretty similar in having a closed low near or over us Tuesday, but it's notable that the FAX charts (UK MET and German) don't, so the human thinking is siding against it. We'll see if they change their minds over the next day or two.

DWD (German) for Tuesday midday.

maquiladora · 13-11-2010 11:19pm

18Z GFS deepens it more but takes the track further west than the last run. I thought the track might come more in line with the ECM/UKMO but seems to be going in the other direction. :rolleyes:

Deep Easterly · 13-11-2010 11:25pm

Indeed Su & Maq, Gerry Murphy didn't alude this either on the RTE weather tonight.

maquiladora · 13-11-2010 11:30pm

Su that chart seems to be the same the 0Z GME at 84 hours, doesn't look like 12Z models were taken into account there?

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gme&MODELLTYP=1&BASE=201011130000&VAR=pslv&HH=84&ZOOM=1&ARCHIV=0&PANEL=0&LOOP=0&INFO=0&WMO=

The later 12Z GME is a bit closer to what the other models on this thread are showing but isn't very interesting :

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gme&MODELLTYP=1&BASE=201011131200&VAR=pslv&HH=72&ZOOM=1&ARCHIV=0&PANEL=0&LOOP=0&INFO=0&WMO=

Pangea · 13-11-2010 11:40pm

Whats a wave depression and what effect has it?

maquiladora · 13-11-2010 11:42pm

18Z NOGAPS is further west too. Still looks windy though.

maquiladora · 14-11-2010 12:01am

Pangea wrote: »

Whats a wave depression and what effect has it?

Its just a secondary low. Same effects : wind/rain.

The example on this page actually looks very similar to what some of the models are showing.

http://science.jrank.org/pages/65031/secondary-depression-%28wave-depression%29.html

Su Campu · 14-11-2010 12:46am

maquiladora wrote: »

Su that chart seems to be the same the 0Z GME at 84 hours, doesn't look like 12Z models were taken into account there?

Correct, the 12Zz run only goes to 72hrs - the 00Z run goes to 108. We'll see what they say in the morning after tonight's...

There's still some uncertainty resulting from the complexity of the upper flow forecast around Monday. Like Carmen, this low will spawn from another larger low off the US east coast, and gets caught by a strengthening jetstreak formed late tomorrow by a blast of arctic airmass down Baffin Bay. But unlike Carmen, this jetstreak doesn't become that strong or longlasting, and splits up Monday night, with the upper trough digging slowly eastwards. I think the exact dynamics of this split are not fully resolved, and this is causing the uncertainty.

In any case, I can't see there being enough upper forcing to cause too much of a wind event, but it remains to be seen what we get in the way of rain from it.

maquiladora · 14-11-2010 12:57am

Here is the latest UKMO 72 hour FAX which does show the secondary low developing to our southwest. (The 84 hour chat hasn't been updated yet)

Looks like there wasn't much adjusted there from the 12Z UKMO model run.

maquiladora · 14-11-2010 9:16am

0Z ECM

72 Hours

96 Hours

maquiladora · 14-11-2010 9:31am

Looking at the other 06Z and 0Z models, there has been a very clear shift to the west on the track of this thing. Models will probably shift even further west later and right now I'd say the chances are this will end up being well out at sea. Chances of strong winds impacting us from this are falling.

Deep Easterly · 14-11-2010 5:04pm

maquiladora wrote: »

Looking at the other 06Z and 0Z models, there has been a very clear shift to the west on the track of this thing. Models will probably shift even further west later and right now I'd say the chances are this will end up being well out at sea. Chances of strong winds impacting us from this are falling.

GFS 12z run keeping up this theme also, potentially some very strong winds just off the west coast but the best worst of them missing us.

maquiladora · 14-11-2010 5:19pm

Deep Easterly wrote: »

GFS 12z run keeping up this theme also, potentially some very strong winds just off the west coast but the best worst of them missing us.

Yep, gales just touching the very edge of the west coast but its too far away from us really. Same old story...

12Z NAE, UKMO and GME take the same track too. :rolleyes:

maquiladora · 14-11-2010 7:02pm

Couple of the other models still showing something a bit more interesting though :

12Z COMAPS

12Z CMC/GEM

ninebeanrows · 14-11-2010 7:22pm

These waves are notoriously difficult to forecast as exactly when the intensification takes place can alter the end position.

Even right up until 24 hours before the event the path of these vicious wave lows can change.

Important to continue to keep and eye on it because if it did hit land could hit with some extreme winds.

ninebeanrows · 14-11-2010 8:19pm

Runs this evening really ramping up the intensity of this low, as i said before the exact positioning will be subject to big changes.

ECM throws it quite close to the western Seaboard.

A really Vicious system.

Just an unrelated warning, looking well into the ECM run may create unparalleled cold weather ramping, i advise to avoid just at the moment!:D

Su Campu · 14-11-2010 8:27pm

This one's a tricky little fecker, you'd think there's not much there to cause this to intensify, but some of the models want to spin it up all the same. It forms in the right rear quadrant of a small little jetstreak that doesn't last through tomorrow, so for Tuesday there's not much dynamic forcing remaing from above. I think maybe the exact details of this jet may be slightly different between the models and that's what has the GFS so far west and the ECMWF more to the east..... Tomorrow will tell a lot, especially sat pics later in the day and tomorrow night.

maquiladora · 14-11-2010 8:34pm

12Z NOGAPS :

And a closer look at the 12Z ECM :

Just needs to be a bit further east...

But since there is still a good bit of uncertainty with this one, who knows eh?

Deep Easterly · 14-11-2010 10:18pm

This evening's ECM run is also fairly close to its ensemble mean at 72hrs;

General intermodel consensus is for this feature to slip up along the west coast Tuesday night/Wednesday morning. Certainly a tight looking feature as others have said!

Storm 10 · 14-11-2010 10:37pm

Watched BBC weather for the week ahead and the Girl said winds would reach 60mph on Wednesday as a low pressure moves in, she also showed the chart for the weekend and it was totally at odds with Met Eireann who said the weekend would be calm and cold and BBC showed a low pressure moving up from the South. The BBC one is close to what MT is saying

Who do we trust??

Su Campu · 14-11-2010 10:43pm

There's some slight variation in how the ECMWF is handling the upper features in the vicinity of where this low will originate. Comparing its 1800Z forecast wv image to the actual, there is a slight difference in the location of moisture, aswell as the form and intensity of the dark strip just to the south. Will this difference be insignificant when it comes to the crunch? We'll have to wait and see.

For a larger view of the north atlantic, click here and toggle between WV6.2 and Psuedo WV to see the actual and forecast wv images, respectively. Note how well these match in most other areas, showing that the model's on top of things there. The only discrepancy exists in the area highlighted (and in Baffin Bay, but that could be to do with imagery issues with high latitude areas and not with the model)

ninebeanrows · 14-11-2010 10:54pm

Both NAE and GFS 18z take this low further south.

Enough to impact the west coast.

Further deviation would bring a direct hit.

Thanks alot for that very informative post Su.

Deep Easterly · 15-11-2010 12:20am

Weathercheck wrote: »

Thanks alot for that very informative post Su.

+1

Latest Hirlam has a very narrow line of 24m/s + windspeeds occurring in a tight gradient south of the low as it moves up along the coast:

with some strong winds for s and e coasts as well. Will be interesting to see how later runs manage this.

maquiladora · 15-11-2010 1:20am

Yeah 18Z is a slight upgrade. Charts below show highest gusts from the 18Z and 12Z over a period of 5 days.

18Z:

12Z:

maquiladora · 15-11-2010 2:14am

48 hour OPC chart issued at 9pm...

Deep Easterly · 15-11-2010 8:31am

Just a quick sum up of this morning's runs (00z). Main models this morning have this tight little low just far enough to the west for us to escape the worst effects of it. However, it may still need watching just in case as this fairly deep wave depression is forecast to be forced up against rapidly rising pressure over Scandinavia by a destabilising airmass rushing beneath it from the Atlantic, which is just one of the factors I think as to why the models are are keen to keep the isobaric gradient tight around its center as it passes close to Ireland:

Whether or nay, still looks like it could be blustery/windy enough tomorrow evening as the frontal zone makes it way up over the country.

maquiladora · 15-11-2010 9:38am

Yeah I don't see any upgrade on the 0z models, there seems to be pretty good agreement now on the track. Looks like it will be wet and windy, but not stormy...(if it turns out like the models now show)

Met Eireann is going for "strong to gale fore and gusty south to southeast winds".

Meanwhile, the latest OPC 48 hour chart has :

Su Campu · 15-11-2010 10:44am

Tomorrow's system could be given the name Felice or Gundula. I'd prefer Gundula because cos it's so.....Irish sounding! :rolleyes:

http://www.met.fu-berlin.de/adopt-a-vortex/tief/

maquiladora · 15-11-2010 11:19am

06Z NAE has the low a bit further south and east from 33 hours on.

06Z GFS seems to have very little change from the 0Z over the next 48 hours.

Su Campu · 15-11-2010 2:44pm

Looking at the marine observations at midday I wonder if the low centre is a little further south than the models are predicting. There are two important ships in the area - A8SF8 at 42.3N 34.6W and A8HJ8 at 40.4N 39.7W (both down the bottom of the chart). The nearest one to the centre is A8SF8 at 1001.0hPa, and is reporting a wind from 130° (SE) and the other is at 1004.3hPa and reporting a westerly wind (270°). These wind directions would put the centre somewhere between the two, at around 42N 38W, nearest to A8SF8. But the GFS has the centre further north than that, at around 44N 37W, which is around 120 miles of a difference. It will be interesting to see if there's a southward shift in the 12Z analysis.

200motels · 15-11-2010 3:18pm

An interesting few days ahead, my gut feeling is that it won't surmount to anything major.

maquiladora · 15-11-2010 3:31pm

I think you might be right Su. I took this grab of the sat loop on the 12:15 frame with the LatLon overlay on. I put a red dot where on the animation the centre of the low appears to be. Looks spot on with your co-ordinates for 12:00.

maquiladora · 15-11-2010 4:25pm

Hmmm, 12Z NAE has shifted it slightly north rather than south though...

maquiladora · 15-11-2010 5:18pm

12z gfs has gales/strong gales for exposed coastal areas from the southwest to the northwest with storm force winds just offshore in places.

Su Campu · 15-11-2010 6:45pm

The GFS 12 run has analysed the centre a little to the south, as I though it would. This takes it slightly further away from the jet and the divergence aloft, which could weaken and slow it down. Whether it's enough to cause a larger change come the time we'll have to wait and see. The output for tomorrow 12Z does have it a little further west

maquiladora · 15-11-2010 7:02pm

Based on the 12z GFS

Quite windy in the west/northwest tomorrow evening :

Gusts of 100 / 110kph extending inland a bit in places :

Quite heavy rain in the south :

M.T. Cranium · 15-11-2010 7:03pm

Looks to me as though western coastal counties could see a brief period of strong winds with gusts to 60 mph or so, and potential for somewhat higher, CMC or GEM has a more aggressive solution than GFS and brings the low to within 3 deg of the coast. This is almost ideal for maxing out gusts at Valentia and Belmullet. Storm begins to remind me of that intense windstorm in Kerry last January. Given the short life cycle and current formative stages, probably won't get much clarity on this until the 00z model runs. Have it covered in forecast for this range of outcomes.

Su Campu · 15-11-2010 7:55pm

Here are today's 12Z winds for 18Z and 21Z tomorrow, showing some pretty intense conditions along the south and west. They could be almost as strong as Carmen but for a much shorter period.

maquiladora · 15-11-2010 10:07pm

ninebeanrows · 15-11-2010 10:48pm

Update 18z data would renew concern that is certainly still possible for this vicious feature to hit land.

A definite movement southward and delayed intensification is forecast.

If this signal is built upon in the Morning, some western districts should prepare for the poss of >70mph gusts while Irish sea coasts could see some gusts approaching 60mph.

ninebeanrows · 15-11-2010 10:56pm

I'd say the Met will watch this one overnight.

ECM earlier stalled it to our west before pushing it south and east during Wednesday.

I say the position of this LOW in 24 hours time is uncertain upto 75 miles.

maquiladora · 15-11-2010 10:56pm

18Z GFS has the storm a littler further south and east tomorrow evening, as a result, its a slight upgrade for the west/northwest coast on this run.

55 knots over Belmullet there.

maquiladora · 15-11-2010 11:00pm

Any guesses for top gusts tomorrow? Im going for 120kph at Belmullet. :pac:

Iancar29 · 15-11-2010 11:03pm

Lads , i dunno bout this one.... i still havent recovered from chasing Carmen! .... Whos gonna tag in for me and Winger_pl for this one!? ha

Looks good! , wouldnt be surprised if it gets a bit stronger even.

JanuarySnowstor · 15-11-2010 11:03pm

This little fella is going a tad un-noticed with all the talk about the weekend Easterly.
However a slight nudge East and a slight strength increase and it's a full blown storm!

ninebeanrows · 15-11-2010 11:20pm

Just looking at some SAT imagery, haven't been able to check comprehensively but the system does to me appear to be moving further south, possibly a delay in intensification?

Thoughts?

Su Campu · 16-11-2010 12:19am

ESTOFEX have a Level 1 out for Ireland for strong/severe wind gusts and tornadoes.

showforecast.cgi?lightningmap=yes&fcstfile=2010111706_201011151958_1_stormforecast.xml

showforecast.cgi?lightningmap=yes&fcstfile=2010111706_201011151958_1_stormforecast.xml

Storm Forecast
Valid: Tue 16 Nov 2010 06:00 to Wed 17 Nov 2010 06:00 UTC
Issued: Mon 15 Nov 2010 19:58
Forecaster: KOROSEC

A level 1 was issued for Ireland and areas towards extreme NW Iberia mainly for strong/severe wind gusts and brief tornadoes.

A level 1 was issued for much of central Mediterranean mainly for strong winds, excessive convective rainfall as well as a couple of waterspouts.

SYNOPSIS

A well defined upper cut-off low over northern Mediterranean slowly makes its SE-ward progress. Associated with this upper low, a frontal system will be the focus for convective activity along the surface cold front across Italy and surrounding areas.

Another feature of interest will be rapidly deepening surface low beneath the robust slowly negative tilting upper trough west of UK. Strong surface cyclone moves towards NE just west/near Ireland during the forecast period.

Upper ridging builds up over North and East Europe and western Russia.

DISCUSSION

... Ireland ...

During the morning hours, rapid cyclogenesis takes place just west of Ireland and moves towards NE during the day. A strong cold front extends from its center towards SW and will be moving east towards UK, France and NW Iberia. With rather strong WAA ahead of the front and coming steep lapse rates aloft, some destabilization and convective cells/line is likely to occur along the surface frontal convergence. Mostly, strong to severe wind gusts will be the primary threat. Closer to the low, better veering profiles suggest enhanced SR helicity which could bring some organized rotating convective cells as well. A couple of funnel clouds or brief tornadoes cannot be excluded there either. Behind the front, strong CAA moves towards the continent with numerous shallow convective cells.

... central Mediterranean ...

Beneath the rather well organized upper low, surface cold front moves across Italy during the forecast period. Well mixed BL airmass ahead of it suggest that at least marginal instability will be available and some hundreds of MLCAPE should release. At mid-levels, moderately strong jet wraps around the vort-max with 20-25 m/s of deep-layer shear, which will be favorable enough for locally organized storms. Current thinking is that organized convection will be more likely over open seas and affect coastal areas with some strong winds and intense rain. Excessive (partly convective) rainfall is also expected around northern Adriatic sea where again a rather high precipitation sums are suggested by the models.

In the wake of the core, cold air advection will overspread the Tyrrhenian sea and where quite high LL buoyancy enhances threat for a couple of waterspouts, as wind field will be rather weak.

Iancar29 · 16-11-2010 12:30am

Su Campu wrote: »

ESTOFEX have a Level 1 out for Ireland for strong/severe wind gusts and tornadoes.

OHHH!...

Winger_PL · 16-11-2010 12:43am

If it wasn't for he fact that it'll be dark when this comes I'd consider driving out again as I just got a new camera this weekend...

Wave Depression Watch 16th/17th November - Low Risk of Intense Storm

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