Ex Katia storm thread - TECHNICAL DISCUSSION, FORECASTS AND OBSERVATIONS ONLY!

Hooter23

Poochie05 wrote: »

I found this thread extremely informative, thanks to the knowledgeable contributors. I also came across some interesting historical data in this paper whcih might interest some of you:
http://www.intechopen.com/source/pdfs/15321/InTech-The_impact_of_hurricanes_on_the_weather_of_western_europe.pdf

The paper refers to the highest recorded value of 182km/hr from Debbie in 1961 at Malin Head and Debbie also generated the highest values for sustained winds.

Its says debbie was still a hurricane when it reached here I thought we dont get Hurricanes here like the bbc weather mentioned a few days ago

Poochie05

It refers to them all as hurricanes (with the exception of 2tropical storms) but it also says that:
"It must be noted that at this stage they are no longer true hurricanes as they do not have the high wind speeds and low barometric pressures associated with true hurricanes."

Su Campu

Poochie05 wrote: »

It refers to them all as hurricanes (with the exception of 2tropical storms) but it also says that:
"It must be noted that at this stage they are no longer true hurricanes as they do not have the high wind speeds and low barometric pressures associated with true hurricanes."

That's a very weak comment coming from someone in his position. It would appear from this that he classifies a storm to be a hurricane based purely on windspeed and pressure, when in fact there are other more important factors to be considered, such as a warm core, non-frontal, a tight wind field around a central eye, the presence of upper outflow, etc. Pretty much every year we see at least north Atlantic depression with central pressures as low as 940 hPa and hurricane force winds, so based on these two factors would he classify them as hurricanes?

The fact that he doesn't mention the other factors is a big flaw in his article. Having said that, it is a very informative and useful piece.

Poochie05

Su Campu wrote: »

That's a very weak comment coming from someone in his position. It would appear from this that he classifies a storm to be a hurricane based purely on windspeed and pressure, when in fact there are other more important factors to be considered, such as a warm core, non-frontal, a tight wind field around a central eye, the presence of upper outflow, etc. Pretty much every year we see at least north Atlantic depression with central pressures as low as 940 hPa and hurricane force winds, so based on these two factors would he classify them as hurricanes? ...

I wouldn't know enough about the technical stuff to have picked up on that, so I bow to your superior knowledge. I just thought it was a useful source of historical wind speed data for comparison with those in the last few days.

M.T. Cranium

Mentioned way back in this thread that Debbie was classified as a hurricane quite far into the approach to Ireland back in 1961, but they had a different understanding of extratropical transition at that time. The NHC historical map shows Debbie as a hurricane to the north edge of the map in Donegal Bay, where it was situated at 12z 16 Sep 1961 after brushing land moving NNE across Westport.

As we have no satellite imagery from that far back, we can't be sure, but with the origins closer to the Azores, I would imagine Debbie had completed extratropical transition by about 49-50 N to the southwest of Valentia. It's all academic anyway because the hurricane force winds were still present, but looking at maps of recorded wind speeds, these strongest winds were further from the track than you would expect with an intact hurricane.

Anyway, it will probably be a long, long time until there's another Debbie, just getting a strong storm of any kind on that particular track is unusual. The Oct 1987 storm followed a somewhat similar path about 5 deg further east but then it was never a tropical cyclone.

I would suggest that someone with access to historical weather records start up a 50th anniversary thread since that's rapidly approaching (Friday).

M.T. Cranium

By the way, found this thread posted a couple of years ago.

http://www.boards.ie/vbulletin/showthread.php?t=2055661187

Map from newspaper report shows the track a little west of the NHC track with no landfall although very close to Belmullet. Strongest wind axis from about Shannon to Malin Head.

Central pressure on the map was nothing extreme, about 964 mbs but presumably it was lower at 06z when west of Valentia.

Wetterzentrale seem to have withdrawn their historical weather maps for free viewing, perhaps we should take up a collection and buy the DVD.

Su Campu

M.T. Cranium wrote: »

Wetterzentrale seem to have withdrawn their historical weather maps for free viewing, perhaps we should take up a collection and buy the DVD.

Seems to be working for me here MT, though there's nothing too spectacular shown for Debbie http://www.wetterzentrale.de/topkarten/fsrea2eur.html

M.T. Cranium

Thanks, SC, I'll have to go back into wetterzentrale and see what I did wrong earlier, the menu had changed from the last time I visited for historical maps. They've added maps for every 12 hours now which is great. You have to wonder how accurate they are comparing the 12z map with the newspaper map, as you say, central pressure on the wetterzentrale map is hardly below 980 mbs. But the upper air map tells the story, that jet stream depiction is a raging southwesterly.

We don't seem to get these full-latitude troughs as often in recent years as "back in the day." I've noticed this in North America also, storms like the 1938 hurricane or Hazel (1954), the superstorm of Jan 26, 1978, come to mind as examples of storms that were captured in full-latitude troughs and drawn NNE or even due north. That's the killer direction for windstorms, it seems, because of the rapid energy transfer that can develop.

dsmythy

M.T. Cranium wrote: »

Thanks, SC, I'll have to go back into wetterzentrale and see what I did wrong earlier, the menu had changed from the last time I visited for historical maps. They've added maps for every 12 hours now which is great. You have to wonder how accurate they are comparing the 12z map with the newspaper map, as you say, central pressure on the wetterzentrale map is hardly below 980 mbs. But the upper air map tells the story, that jet stream depiction is a raging southwesterly.

We don't seem to get these full-latitude troughs as often in recent years as "back in the day." I've noticed this in North America also, storms like the 1938 hurricane or Hazel (1954), the superstorm of Jan 26, 1978, come to mind as examples of storms that were captured in full-latitude troughs and drawn NNE or even due north. That's the killer direction for windstorms, it seems, because of the rapid energy transfer that can develop.

Maybe this just means we are way over due such an episode on either side of the Atlantic

Hooter23

M.T. Cranium wrote: »

By the way, found this thread posted a couple of years ago.

http://www.boards.ie/vbulletin/showthread.php?t=2055661187

Map from newspaper report shows the track a little west of the NHC track with no landfall although very close to Belmullet. Strongest wind axis from about Shannon to Malin Head.

Central pressure on the map was nothing extreme, about 964 mbs but presumably it was lower at 06z when west of Valentia.

Wetterzentrale seem to have withdrawn their historical weather maps for free viewing, perhaps we should take up a collection and buy the DVD.

What I dont understand is how the pressure is not that low really but yet the winds were so strong is it different because these storms originated in tropics also why is there not that many isobars on that chart if it was so windy?

Su Campu

Going on the GFS reanalysis - for what it's worth - the storm is moving northwards at around 30-35 knots, so this motion would be added to the winds to the east of the centre, i.e. the exact area from Shannon to Malin that did in fact get the strongest winds.

Deep Easterly

Hooter23 wrote: »

What I dont understand is how the pressure is not that low really but yet the winds were so strong is it different because these storms originated in tropics

One reason is that it isn't so much to do with how low the MSLP value is but what its value is relative to surrounding high pressure zones. Storm Udo back in May for example was a stronger system than the one we got a couple of days back yet MSLP values were not exceptionally low:



Mean sea level pressure values did not fall below 976mb in the storm center as it passed to the north of Ireland on the 23rd May but with intense high pressure zones over nearby Europe, the Azores and south of Greenland (with MSLP values between 1027-1029mb) this helped to increase or 'squeeze' the isobar/ pressure gradient substantially between these ridges and the low center, which in turn helped to increase windspeeds to the south and west of this depression especially.

Su Campu

Strange that it was analysed as 976 hPa when ship BATFR04 reported 974.1 hPa near the centre!

http://www.ogimet.com/cgi-bin/gsynop?lang=en&zona=eur0&base=bluem&proy=orto&ano=2011&mes=05&day=23&hora=06&vwi=Wi&vpr=Pr&Send=send




EDIT: Just zooming in on that map I see that buoy 64049 just west of Belmullet reported mean winds of 68 knots :eek::eek::eek:....I wonder if that can be right??!!! It was 44 knots 3 hours before. Waves were reported as 7 metres, which seems a bit low for such a speed.

Click and hover over the wind barb west of Belmullet.
http://www.ogimet.com/cgi-bin/gsynop?lang=en&zona=uk&base=bluem&proy=orto&ano=2011&mes=05&day=23&hora=06&vwi=Wi&vpr=Pr&Send=send

Elmer Blooker

Hooter23 wrote: »

Its says debbie was still a hurricane when it reached here I thought we dont get Hurricanes here like the bbc weather mentioned a few days ago

Morning Ireland on RTE radio did an item on "Debbie" - today being the 50th anniversary. Gerry Murphy said it was a category 1 and the only hurricane ever recorded in Ireland. Sixteen people died in Ireland including four from one family in Co. Cavan. There was only one death from Katia and that was in Durham, NE England so it shows how severe Debbie was.

Su Campu

I heard that too, he said it's the "only intact hurricane that's reached Ireland". I don't agree with him, and here's why.

As MT said above, things were different back then, and while hurricane force winds were recorded in Malin Head, the storm's motion had a lot to do with that. The US Weather Bureau (as it was then) said it was not a hurricane, even Met Eireann in their article on it said so too. Plus this chart shows it's extratropical.

Deep Easterly

This is a reply to a question put forward to met eireann's Climate Enquiries Office a couple of years back when this same debate was going on on some other thread:

Met Eireann wrote:

Patrick,
“The dynamic nature of tropical storms and mid-latitude cyclones differ. Tropical storms are warm core, mainly closed cell systems, requiring a sea surface temperature (SST) of at least 26 Celsius and high humidity, the latent heat released as warm, humid, air rises and condenses is converted to kinetic energy as wind if the right conditions exist. Mid latitude (30-60 N) cyclones form under the jet stream where warm and cold air masses meet, resulting in the formation and development of low pressure areas at the surface.

Tropical storms become extratropical as they move Northwards and the SST decreases, at this stage they also come largely under the influence of the wider atmospheric circulation, including the jet stream. The rapid cyclogenisis in the ‘Debbie’ case is a clear mid-latitude extra tropical phenomena. We would not consider ‘Debbie’ to have been tropical storm when reached in Ireland, although it retained many hurricane characteristics”

I too heard Evelyn Cusack and Gerry Murphy refer to Debbie as a 'tropical storm' and 'hurricane' respectively on the radio this morning. I seriously doubt though that either Evelyn or Gerry were basing their comments solely on the technical side of what defines a hurricane but what the actual experience of ordinary people was or would have been during the height of Debbie. In the same way, professional meteorologists in Ireland often describe conditions as 'stormy' when actual mean windspeeds are no where near storm force, such as when 'Katia' hit last week.

Anyway, whether technically a hurricane or not, mean wind speeds did reach hurricane force at Donegal's Malin Head during a 2 hour period :eek: between 1pm and 3pm as Debbie's storm's centre skirted along the northwest coast.

Below is a chart showing hourly maximum 10 minute mean windspeeds on the 16th September 1961 at Malin Head. Also included is the hourly wind direction recorded at that station in the horizontal axis:


Data C/O International Journal of Climatology/University of Ulster.

The strongest winds began at Malin Head when when wind direction suddenly veered from a SE to SSW direction during the afternoon which suggests that the most severe winds occurred once the main frontal zone passed over. Wind direction remained from a SSW direction during the height of the storm and only eased a little once winds veered further to the SW during the late afternoon and evening.

No place in Ireland escaped these winds however, but without a doubt the western half of the island bore the brunt as the chart graphing mean and max windspeeds at recording met eireann stations shows:


Data source: Met Eireann

From what I can gather from listening to stories and researching old newspaper reports the storm seemed to peak in Connacht and Leinster sometime between 10am and 12am, and somewhere between 9am and 11am in Munster.

Interestingly, there was not much rain contained in the frontal zones ahead of the storm. Although Valentia recorded 20mm on the 16th, most stations, including Malin head, did not record rainfall totals above 2 or 3mm for the entire day! (the 15th was a wetter day in places).

Headline in the Irish Times on the 18th September 1961:



The tragic consequences of Debbie's infamous visit to Ireland 50 years ago today.

sdanseo

Strange that those figures use a 10-minute windspeed, the NHC use 1-minute sustained. Any reason for this?

Pangea

http://www.rte.ie/news/2011/0920/cork.html

It looks like this yacht may have got caught up in the Hurricane.

gbee

Pangea wrote: »

It looks like this yacht may have got caught up in the Hurricane.

A spokesman for the coastguard service in Bermuda said the yacht would have been sailing through an area of the Atlantic where the tail end of Hurricane Katia was still active.

This summation cannot be very accurate, or the map showing the 'route' is garbage ~ Katrina remnants were quite far northerly.

There were other fish TDs that the yacht might have encountered for sure.

Pangea

Katia was on route from Bermuda to Ireland, its possible the yacht was caught up in the middle of it.

gbee wrote: »

This summation cannot be very accurate, or the map showing the 'route' is garbage ~ Katrina remnants were quite far northerly.

The map shows the yachts route not Katias.

gbee

Pangea wrote: »

The map shows the yachts route not Katias.

Absolutely, why do think I said what I did. I know very well it's not Katia's route, we don't know if it's the yacht's route ~ in fact I say it's not, they would tend to go more northerly or southerly, they hardly ever cross in a bee line like illustrated.

It's possible she took a northerly route and then intercepted Katia's remnants while they were still strong.

If she took the more southerly route, we do have TD's she'd have met.

gbee

Katia's route

http://www.stormpulse.com/hurricane-katia-2011

Pangea

By 'TD' I take it you don't mean the guys in the Dail. :pac:
What's a TD?

gbee

Pangea wrote: »

By 'TD' I take it you don't mean the guys in the Dail. :pac: What's a TD?

Tropical Depression

Su Campu

This is the great circle route (i.e. shortest) from Bermuda to Cork, which is nearer to Katia's path than the RTE map shows. The yacht left on August 21st, so it could have been caught up in Irene too, which was in the area around that time.

In any case, heavy swell can be felt many hundreds of miles away from a storm