August rains, past and present

Mothman

Rainfalls at Shannon and Dublin APs need to be mentioned.

6th August 2008
38.4mm in an hour at Shannon AP 16-17z.
Highest one hour fall at a synoptic station. There have been much higher one hour falls away from synoptic stations, with one mentioned on Met Eireann website

9th August 2008
76.2mm at Dublin AP. 2nd highest daily (00-24z) fall on record at Dublin AP.

Mothman

Not half way through and its the wettest August at Dublin AP since at least 1956 and probably on record.

158.8mm up to end of 13th, surpassing the 158.7mm in 1986, the H. Charley year.

Deep Easterly

Mothman wrote: »

Not half way through and its the wettest August at Dublin AP since at least 1956 and probably on record.

158.8mm up to end of 13th, surpassing the 158.7mm in 1986, the H. Charley year.

Might be interesting to keep an eye on rainfall totals for this August and to compare them to the 86 totals, as we certainly are going through a wet period that is comparable to that year:

Chart of totals for August of both 86 and 08, with deviation. Only Dublin Apt has surpassed so far, but considering it is only the 14th, not bad at all!



Dublin has broke the barrior, will be interesting to see if other stations will do this over the next couple of weeks.

Mobhi1

Deep Easterly wrote: »

Might be interesting to keep an eye on rainfall totals for this August and to compare them to the 86 totals, as we certainly are going through a wet period that is comparable to that year:

Chart of totals for August of both 86 and 08, with deviation. Only Dublin Apt has surpassed so far, but considering it is only the 14th, not bad at all!



Dublin has broke the barrior, will be interesting to see if other stations will do this over the next couple of weeks.

Shannon has too but it's a lower barrier.

Mothman

Though Shannon recorded 229.5mm in 1997, so a long way to go, though is more than half way at the mid point of month.

Mobhi1

Mothman wrote: »

Though Shannon recorded 229.5mm in 1997, so a long way to go, though is more than half way at the mid point of month.

Is that the highest ever August rainfall in the country? Another day like last Saturday (which is unlikely) or weekend and Dublin Airport would exceed it.

Mothman

Mobhi1 wrote: »

Is that the highest ever August rainfall in the country? Another day like last Saturday (which is unlikely) or weekend and Dublin Airport would exceed it.

No most other stations have had higher.
Valentia recorded 272.9mm in 1985.

I have data only from 1958 onwards.
There have been much higher totals away from synoptic stations,

Dhulough Co. Mayo 374mm Aug 1992

nacho libre

Dhulough Co. Mayo 374mm Aug 1992


I find that figure really hard to believe. There must have been monsoon conditions everyday of that month for 12 hours a day to register a rainfall total like that.

Mobhi1

nacho libre wrote: »

Dhulough Co. Mayo 374mm Aug 1992


I find that figure really hard to believe. There must have been monsoon conditions everyday of that month for 12 hours a day to register a rainfall total like that.

I don't know, Dublin Airport's had just a bit less than half that in half a month and it hasn't been monsoon conditions every day. It's been fairly wet alright but it seems to have been mostly made up of one extremely wet few hours and a couple of wet days plus a some rain on most of the other days but there were also a few dry days in there as well. Even on the extremely wet day the rain didn't really start until late afternoon and was mostly finished by late evening - just a few hours of torrential rain. And that's on the east coast.

Supercell

nacho libre wrote: »

Dhulough Co. Mayo 374mm Aug 1992


I find that figure really hard to believe. There must have been monsoon conditions everyday of that month for 12 hours a day to register a rainfall total like that.

Its easily doable, sure didnt Kippure have at least that in one day during hurricane Charley? An extreme event yes, but spread over 31 days this doesn't seem unreasonable of an exposed site in the west.

Mothman

nacho libre wrote: »

Dhulough Co. Mayo 374mm Aug 1992


I find that figure really hard to believe. There must have been monsoon conditions everyday of that month for 12 hours a day to register a rainfall total like that.

I don't know the location of Dhulough, and whether it is another name for Doolough.
Perhaps our Mayo man on the spot can shed some light.

As for that total. 72mm fell on the 22nd, leaving 300mm over 30 days, an average of 10mm a day, quite believable.

Maam Valley Co. Galway, recorded 370.3mm same month, Aug 92. Difference being "only2 65mm on the 21st.

A few hills can make a huge difference to rainfall. Supercell is proving that. 13k west of me, but sometimes recording double or more rainfall

Mothman

August 97 has to be mentioned.
4 day totals of up 250mm were measured over many parts of the southern half of the country between the 3rd and 6th.
Daily total of around 150mm was recorded at some locations in Co. Wexford on the 3rd.

Thinking back, I think all this was not forecasted. A sunny bank holiday weekend was forecasted. Hay was cut, grain harvesting put off.....what followed was a deluge not matched yet in 2008.
Totals for month included 295.7mm at Johnstown Castle
261.2mm at Rosslare, wettest month on record there until exceeded in Oct 02.

Deep Easterly

Mothman wrote: »

Big rainfalls in Galway and Mayo in August 1992 (paraphrase)

Budge over Nacho, and make room for Supercell. He's on his way..:D

Edit: Mothman, do you have rainfall figures off hand for all the months of the last few years? It might be interesting to do up a table representing each Station's absolute wettest month. (regardless of time of year). Just might be handy to have a quick reference to compare other wet months with down the line.

(That's not a forecast by the way)

Mothman

Supercell wrote: »

Its easily doable, sure didnt Kippure have at least that in one day during hurricane Charley?

The Kippure fall was estimated to be 280mm

Mothman

Deep Easterly wrote: »

Edit: Mothman, do you have rainfall figures off hand for all the months of the last few years? It might be interesting to do up a table representing each Station's absolute wettest month. (regardless of time of year). Just might be handy to have a quick reference to compare other wet months with down the line.

Overall since 1958 and highest during noughties
Belmullet 259.5mm Oct 89, 257.7 Oct 00
Birr 179.9 Dec 59, 145.2 Aug 07
Valentia 319.5 Dec 59, 302.4 Oct 00
Casement 178.9 Oct 02
Cork AP 340.9 Jan 74, 242.4 Jan 02
Dublin AP 217.0 Dec 78, 186.3 Nov 02
Malin Head 250.4 Oct 90, 188.8 Jan 08
Mullingar 205.1 Nov 65, 177.9 Feb 02
Shannon AP 239.8 Dec 59, 220.7 Jan 08

Mothman

BTW, and off topic
Maam Valley 590mm Dec 06

Supercell

Good heavens, 590mm, even I might start to get a bit bored of it

This month could yet be a record breaker, I wouldnt be in the slightest bit surprised to surpass 200mm which is going to take some beating here.

I'm in a bit of a dry spot here for this elevation, Laragh and Roundwood get considerably more and Calary far far far more, wouldn't be surprised if Calary totals are already in excess of 300mm for the month..they also get a lot more snow there..no prizes for guessing where I will some day own a house )

Deep Easterly

Mothman wrote: »

Overall since 1958 and highest during noughties
Belmullet 259.5mm Oct 89, 257.7 Oct 00
Birr 179.9 Dec 59, 145.2 Aug 07
Valentia 319.5 Dec 59, 302.4 Oct 00
Casement 178.9 Oct 02
Cork AP 340.9 Jan 74, 242.4 Jan 02
Dublin AP 217.0 Dec 78, 186.3 Nov 02
Malin Head 250.4 Oct 90, 188.8 Jan 08
Mullingar 205.1 Nov 65, 177.9 Feb 02
Shannon AP 239.8 Dec 59, 220.7 Jan 08

Cheers MM. Will do up some tables with percentages etc for prosperity over the next few days and post them in a seperate thread for future comparative analysis.

Ps, you have no figures for Claremorris by any chance?

redspider

Mothman wrote: »

Belmullet 259.5mm Oct 89
Birr 179.9 Dec 59
Valentia 319.5 Dec 59
Casement 178.9 Oct 02
Cork AP 340.9 Jan 74
Dublin AP 217.0 Dec 78
Malin Head 250.4 Oct 90
Mullingar 205.1 Nov 65
Shannon AP 239.8 Dec 59

The problem with rain mm values in a given period is that it is a statistical sampling, and rain by its nature is a very sporadic and concentrated phenomenon. Thus small sample times (daily, even one month, or a year) do not produce a long-term average amount.

For example, the daily figures of any measuring point does have its daily amount affected hugely by when the rain actually falls, eg: a 6 hr burst of rain could be spread over 2 days if it started at 21:00 but would occur within one 24-sampling period if it started at 18:00 or earlier. Thus many many sample points are needed to generate averages. Met Eireann state here ( http://www.met.ie/climate/rainfall.asp ) that approx 66% of all measured hours are dry. Ireland, hard to believe is actually more dry than wet! Fact.

With such a scenario and with "large" 1 hr rainfall of 100mm possible, even monthly averages as posted above will be affected by the sampling. Perhaps by measuring over 1000 years or so, we would have more definitive values of monthly peaks.

Mothman, what are the values for 2-months per station, or 3-months per station, etc? These would likely show a levelling off and values for each station becoming closer together, percentage wise, standard deviations, etc. 12-months is of course the yearly average. And 24-month averages would be better again.

Another aspect about rain, is that for many people in the modern era (although clearly not many of the engineers and planners that have designed areas of Ireland's drainage network), its not the amount of rain that falls that matters but the amount of time the rain is falling. And it becomes subjective, when does very light drizzle really become rain. The differences in 'traces' are hard to measure. Are there any stations anywhere that measure the time that rain falls?

By the way, Ireland is a relatively dry place compared with Reunion, where within 48 hrs on April 8-10 in 1958 a World record (for 48 hours) of 2,467 millimetres fell. Think Dublin's recent 76mm day x 16, and for 2 days in a row!

By the way, any jetstream weather predictions going around?
Are these Low depressions gonna stop rolling in soon?

Redspider

Mothman

Deep Easterly wrote: »

Ps, you have no figures for Claremorris by any chance?

No data for Claremorris since 1996
Up till then 258.6mm Aug 85

nacho libre

Supercell wrote: »

Its easily doable, sure didnt Kippure have at least that in one day during hurricane Charley? An extreme event yes, but spread over 31 days this doesn't seem unreasonable of an exposed site in the west.

Yes, you're right. I don't know what i was thinking. Let's just hope this sort of woolly thinking is not in evidence when it comes to my predictions for September in the weather league
by the way how have you been sleeping lately?:pac:

nacho libre

Mothman wrote: »

I don't know the location of Dhulough, and whether it is another name for Doolough.
Perhaps our Mayo man on the spot can shed some light.
/QUOTE]


if i'm not mistaken Doolough (Dubh Lough or Black Lake) is on the road from Louisburgh to Killary Harbour and Leenane.

there is also Doolough Strand, Gweesalia, Blacksod Bay.
This beach is on the eastern side of Blacksod Bay, Co. Mayo, on the Doolough Peninsula, north-west of Gweesalia.

Mothman

nacho libre wrote: »

Mothman wrote: »

I don't know the location of Dhulough, and whether it is another name for Doolough.
Perhaps our Mayo man on the spot can shed some light.
/QUOTE]


if i'm not mistaken Doolough (Dubh Lough or Black Lake) is on the road from Louisburgh to Killary Harbour and Leenane.

Yes this is the one. Dhulough pass road is on the OS map.

Smack between two mountains, so not surprising to see high rainfall.