Ex Ts Katia To Hit The UK - Chat Thread

[Robbie Garrett]

Thought I'd start a topic to discuss the above title, I can't see it happening - but 80mph sustained winds gusting 100mph sounds a field day for the MetOffice.

Discuss!

[Methuselah]

Hopefully not. But, should the models all turn out to be woefully wrong at the same time (not entirely unheard of) it'll be slithering along between Shetland and Iceland. Not quite out-of-harm's-way - but near enough.

[Aaron]

I hope so. I'd enjoy a bit of exciting weather rather than the boring rubbish we have at the moment had all year.

Edited September 7, 2011 by aaron

[Coast]

Just a couple of piccies I posted over in the current Katia thread illustrating what is currently forecast by the Americans:

+ a reminder that Nick F is following Katia in the NW forecasts here:

http://www.netweather.tv/index.cgi?action=news;storyid=790;sess=

[Robbie Garrett]

Looking at this, NHC still show Hurricane Katia as a Hurricane north of Scotland, isit me or am I going blind? but it does say H??

[Coast]

Looking at this, NHC still show Hurricane Katia as a Hurricane north of Scotland, isit me or am I going blind? but it does say H??

Well technically it will be an Ex-Tropical storm I beliveve, but it may have hurricane force winds.

[Harry]

Quite right it does say H!

It does appear to be following the perfect line above the Gulf Stream, however I'd be gobsmacked if the Gulf Stream is sufficiently warm enough to fuel a Hurricane.

The white circle does show it to be 'post tropical' however (so unsure why the 'H')

[Carl46Wrexham]

Wanting "exciting" weather is one thing.....hoping that this thing has a direct impact on the UK as I have seen a few people posting such on other forums is quite another. Were this storm to directly hit us, there would undoubtedly be significant loss of life...so no thank you on this one.

Edited September 7, 2011 by Carl43Wrexham

[Robbie Garrett]

Well technically it will be an Ex-Tropical storm I beliveve, but it may have hurricane force winds.

I get it now, lol! I've just re-read the Chart and feel like an idiot

Well looking at the charts, its that High Pressure to the south which is forcing Katia northwestwards. Hopefully something changes and Katia's path changes, as that left turn it's making according to NHC NOAA is very annoying.

[Radiating Dendrite]

Yep, it will not longer be a "hurricane" by 120hrs though.

It is not unusual to have Atlantic storms with Hurricane Force winds. Remember the lowest ever recorded pressure in the North Atlantic is 916mb!

[Coast]

Interesting analysis from our friends over at Irish Weather Online:

Hurricane Katia weakened further overnight becoming a category one storm through Wednesday morning. The system is forecast to track between Bermuda and the US east coast before shifting northeast across the Atlantic, eventually tracking to the northwest of Ireland and the United Kingdom.

Later this week Katia, by then an extratropical low, is expected to move east across the Atlantic and track between Iceland and Ireland and the United Kingdom (UK).

According to iWeather Online Senior Forecaster Peter O’Donnell: “There is a moderate risk of stormy weather in the coastal districts of the north and west of Ireland as well as western Scotland.

“The trend on almost all guidance for the extratropical remnant low of Katia is slightly towards stronger wind potential in the northwest of Ireland, as a very intense low is shown within 100-200 miles of Donegal Bay. There is a spread in model solutions, with the UKMO weakest, but the leading models as well as the National Hurricane Center (NHC) predictions show potential for very strong winds as early as Sunday night (peaking Monday morning in most outlooks)”.

“Atlantic marine areas of Ireland can expect possible storm force SW winds by evening, spreading to coastal fringes by early Monday morning. For the northwest on Monday, especially Galway, Mayo and Donegal, there is potential for gales or storm force winds (SW 45-70 mph) with hurricane force winds possible around Donegal Bay and in marine areas west and northwest of the Mayo-Galway coasts. Clare, Sligo, Roscommon and Leitrim into west Ulster are also at risk of some higher gusts.”

But some models have it coming right up The Channel! (not likely I would suggest at this point)

AL122011 BAMD Model Track

*** Computer Models Are Not Forecasts ***

*** Please refer to the OFFICIAL forecast ***

Model: BAMD

Run: 2011090700

[Radiating Dendrite]

Quite right it does say H!

It does appear to be following the perfect line above the Gulf Stream, however I'd be gobsmacked if the Gulf Stream is sufficiently warm enough to fuel a Hurricane.

The white circle does show it to be 'post tropical' however (so unsure why the 'H')

"H" just means hurricane force winds.

[Aaron]

Wanting "exciting" weather is one thing.....hoping that this thing has a direct impact on the UK as I have seen a few people posting such on other forums is quite another. Were this storm to directly hit us, there would undoubtedly be significant loss of life...so no thank you on this one.

I'm not really hoping it directly hits us, obviously loss of life would be very sad indeed, but I can't help but feel somewhat excited about the idea of a proper storm hitting the UK. So, if it does have a direct impact on us, I will certainly make the most of it as a major meteorological event.

[Robbie Garrett]

Does anybody know what's needed to change Katia's direction towards the UK?? I understand that the High Pressure to the south is pushing her Northeastwards mid-atlantic, but what would need to change to get it going eastwards?

[Coast]

Here's an interesting comparison of all September cat 1 and 2 storms that have tracked within 2dg of Katia since 1851 and only two have come close to the UK:

Does anybody know what's needed to change Katia's direction towards the UK?? I understand that the High Pressure to the south is pushing her Northeastwards mid-atlantic, but what would need to change to get it going eastwards?

Read chionomaniacs analysis with regard to the jetstream here:

http://forum.netweat...ost__p__2129489

[Backtrack]

No, I highly doubt it will have a direct impact on the United Kingdom. It's weakening all the time as it heads towards us, and it's track looks like bringing it somewhere in between Iceland and Scotland. The far North of Scotland will see the highest winds, but I honestly cannot see this ex-hurricane disrupting us too badly. Perhaps just a repeat of yesterday's winds?

Edited September 7, 2011 by Backtrack

[chionomaniac]

Continuing on from my earlier post - it does look as if the 6Z GFS has changed little - if anything Katia is a little closer to the UK.

It appears that Katia will cross the STJ at around T+90. If anything Katia seems to interrupt the jet stream flow as much as she is influenced by it:

Secondly, once Katia has crossed the STJ, the direction, strength and angulation of the jet stream will be critical in determining how Katia will affect the UK. If the jet stream holds a little further south and keeps the jet streak in the East Atlantic, then we could see a hurricane strength extra tropical low hit our shores.

[Coast]

Hurricane Katia Discussion Number 37

the cloud pattern of Katia has become a little less organizedovernight. Cloud top temperatures have generally been warming anddry air appears to wrapping around the western semicircle of thecirculation...the latter giving the cyclone a somewhat hollowappearance. In addition...there appears to be northwesterly shearover the hurricane...as evidenced by cirrus cloud motions andconfirmed by UW-CIMSS analyses. Dvorak T- and CI-numbers from TAFBand SAB are lower...and a reasonable blend of these data gives anintensity estimate of 80 kt. An eyewall replacement cycle thatbegan 24-36 hours appears to have been interrupted...with earliermicrowave imagery showing an outer eyewall at large radius that wasnot contracting much. This structure...along with the moderateshear...suggests not much change in strength...followed by only aslow weakening during the next few days as Katia remains overrelatively warm waters. After 72 hours...Katia will quickly move along a strong gradient of SSTs and encounter an increasingly baroclinic environment...both of which should result in a rapid transition to an intense extratropical cyclone. Post-tropicalcyclone Katia is expected to be a significant weather system overthe far North Atlantic for at least a couple of days. The official NHC wind speed forecast is lowered in accordance with the latest intensity guidance and is in best agreement with the model consensus.

I'll just add this from Gibby in the model discussion thread:

In Summary this morning the models continue to handle the ex tropical storm next week rather differently. GFS keeps it as a very intense feature well away to the NW which benefits the UK as it pumps up warm and higher pressure from the South bringing decent weather eventually after a strong blow for a day or two with rain at times. UKMO and ECM keep it a shallower feature but closer to our shores continuing the unsettled, windy theme going. The most worrying thing of note this morning is the return later of rising pressure near Greenland and the Atlantic from ECM pulling winds round towards the Northwest and keeping the UK in increasingly cool showery conditions in response to Low pressure over Scandinavia. The GFS solution couldn't be more different.

[Ja23]

I can't understand why UKMO is not showing anything as serious to the GFS. Anyone know? I'm new to this stuff.

And at the moment I don't think it will hit the UK we may get some windy weather but I think the worse may just miss us.

[A.J]

I'll be quite happy to see the hurricane remnant to plonk itself a few hundred miles to the west off the Irish/scottish coast, and sit there and slowly fill for a few days, meanwhile the rest of us will bask in some lovely humid southerlies pumped up, tea shirt weather with the chance of thunderstorms, perfect for september!

[Radiating Dendrite]

I can't understand why UKMO is not showing anything as serious to the GFS. Anyone know? I'm new to this stuff.

And at the moment I don't think it will hit the UK we may get some windy weather but I think the worse may just miss us.

It is a seperate computer model and will have different data fed into it.

Remember the GFS run that we see is only one of 20. The other 19 runs are fed slightly different data, leading to differences occuring.

[weatherobsuk]

This was the NHC discussion on it last night. I think 'extratropical Hurricane?' may be best to describe Katia

BY DAYS 4 AND 5...BAROCLINIC FORCING SHOULD PREVENT KATIA

FROM WEAKENING TOO MUCH...EVEN OVER COLDER WATERS...AND THE CYCLONE

IS FORECAST TO BE A POWERFUL EXTRATROPICAL STORM OVER THE NORTH

ATLANTIC. THE INTENSITY GUIDANCE IS IN FAIRLY GOOD AGREEMENT...AND

THE OFFICIAL FORECAST IS MAINLY JUST AN UPDATE OF THE PREVIOUS

FORECAST."

[Carl46Wrexham]

I'll be quite happy to see the hurricane remnant to plonk itself a few hundred miles to the west off the Irish/scottish coast, and sit there and slowly fill for a few days, meanwhile the rest of us will bask in some lovely humid southerlies pumped up, tea shirt weather with the chance of thunderstorms, perfect for september!

Now that's the kind of weather I want! By all means bring that on!

[Iceberg]

Katia is definately not be tropical when it gets near our shores all analysis and forecasts show a distinct temperature gradient with a classic wedge causing the winds so very much baroclinic in nature.

IMO the extra tropical transition will either have happened or largely have happened.

Phase analysis from UKMET and GFS 06Z shows the differences as to why METO is not handling this very well at all. UK MET initialises Katia at below hurricane strength due to it's resolution this obviously has knock on impacts as to when the storm gets into the NW Atlantic as it has far less energy.

GFS brings a swave of hurricane strength 925 winds to northern England. Where the METO might be more accurate is the general path of Katia which could well be further south of the GFS set up.

ATM we are probably looking at sustained winds of 70-80 mph and gusts to 90mph for exposed areas for Scotland and Ireland and gusts to 60mph further south.

A point I would make is that we have only had a single recon into Katia due to this very little information is known as to the wind radia, strengths, or the size of the low pressure system. Far less is known than with any normal tropical storm.

How this transfers from tropical to ex tropical to baroclinic is guess work. Due to these factors the models will not have a good steer on path or intensity until T72 to T48.

[Radiating Dendrite]

I think we can safely say it will be strong!

It is the track that will be the interesting thing. Even sustained winds of 40-50mph could do significant damage to inland locations!