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

At 72 hours a significant storm in our southwest approaches.

And a significant remnant of a hurricane

cross-posted from Hurricane Katia thread

I have the feeling that reader interest will swing from this thread to the "Monday threat" thread so I plan to post forecast discussions related to Ireland in that thread from now on.

Katia came very close to ocean buoy 41044 last night and at one point around 06-07z the buoy was in the eastern eyewall and reporting wind gusts to 93 knots or 107 mph.

Katia seems to have regained a bit of strength in the past 18 hours and looks to be heading slightly east of due north near 70 W, about to be swept into the fast flow extending from south of Nova Scotia to north of Ireland.

The NHC gives a Monday 12z position at 59.5N 10W on its latest outlook which would place the strongest winds around 57N 8W but the GFS has the centre just about in that position which would place the strongest winds over Donegal. Since the GFS depiction may be slightly weaker than the NHC's implied map intensity (from their maximum winds) I would estimate the GFS 12z charts to be predicting sustained winds near 55 mph and gusts near 80 mph or 70 knots from 0600 to 0900 Monday. A storm as strong as the NHC forecast in the GFS position would give sustained 60 mph, gusts 90 mph or near 80 knots.

Will be making more extensive model comparisons later on this thread.

GEM shows an intense storm heading across Donegal Bay on a track about 1-2 deg south of the GFS. If it verified, it would create a severe storm across almost all of Ireland on Sunday night into Monday. Winds could gust as high as 80 mph in many regions and to 100 mph in coastal west and northwest as well as exposed higher inland sites, from the map depiction. The key element is a very strong jet stream forced south by phasing of an arctic vortex dropping southeast towards the Rockall marine zone at storm time. With the recent good form of this model, and with the GFS trending in a similar direction, the situation looks very ominous to me. Bear in mind also, comparing RGEM to GGEM (regional 48 hour on a finer scale, global on a coarser grid) the 48h pressure difference near Newfoundland is 5 mbs, meaning the actual storm captured on a finer model grid is then 5 mbs deeper. So the depicted 966 mb low for Monday 12z could be closer to 960 mbs. (position on that about 56N 7W).


UKMO due around 9 p.m.

ECM due around 9:30 p.m.

NOGAPS due around 10 p.m.

Will edit this post for GEM results but anticipating a number of other posts will post the UK, ECM and NOGAPS input together around 10 p.m.

12Z GEM...

The GEM would bring a really strong core of winds to much of Ireland and of particular note, the capital would be struck very hard.

Its position and movement is almost ideal for intense winds in the greater Dublin region.

Just one run of one model and at T+96hrs, a long way to go before it could come off.

Some people I talked to today didn't even hear about the storm coming.
If it is going to be dangerous I hope people will be aware and with the uncertainty the media might not like to put themselves out for criticism.

Somebody just said to me that there will be snow from October onwards though :rolleyes:

Damaging winds would still result from that ECM 96hr.

I would anticipate gusts to max 65mph overland and max 75mph on west coast.

An important thing to note as this system appears it will take a closer hit at the country
is that trees are still fully covered. There will be significant numbers of fallen trees even
if a weak system pushes through.

A few days ago, a number of large branches fell in the high winds. The max gust recorded
at DUB AIR was 43 knots or circa 47mph.

well there goes my plans for staying in youghal next week.

cherryghost wrote: »

It'll probably be reported on the RTE Weather tonight or tomorrow. Met Eireann have already forecast severe or damaging gusts countrywide for Monday.

There was a warning on Jean Byrnes forecast before 7.
She said very strong winds but didn't elaborate really.

High tide is 6.30am Monday for Donegal Bay. What can we expect as regard as storm surge ?

My take on the ECM is that the intermediate position between Sunday 12z and Monday 12z maps would suggest concern even if the storm weakens as depicted by 12z. The implied 06z position in Donegal Bay is similar to GFS-GEM composite. The UKMO seemed to lose the storm again after locating it briefly on the Sunday map.

In general, the trend has me very concerned and I have upgraded the wording of the Boards forecast in the form of an advance alert.

cherryghost wrote: »

It'll probably be reported on the RTE Weather tonight or tomorrow. Met Eireann have already forecast severe or damaging gusts countrywide for Monday.

Saw RTE weather tonight and no sense of impending danger at all! Reading this thread I am much more concerned and excited :eek: but if there is a potential for damage I can't believe ME didn't allude to it.

Media "Batten down the hatches" has begun.

http://www.herald.ie/news/hurricane-katia-heading-our-way-2870989.html

BATTEN down the hatches -- gale force winds are expected to batter Ireland as the tail-end of Hurricane Katia (circled) hits.

Winds of up to 90mph are expected out to sea off the west coast and will still be running at 70mph when they hit land.

The Category Two hurricane is now off the coast of Bermuda, but is heading for Ireland on Monday

The gales may begin as early as Sunday night and will peak on Monday morning with the coasts of Donegal, Mayo and Galway bearing the brunt.

The news comes as it was revealed Ireland is set to be under a blanket of heavy snow within weeks.

Forecasters say temperatures matching last year's record lows of -17.5C are just around the corner.


Love the bit at the end. WHO says this!? :rolleyes:

Very interesting few days ahead no matter what happens, Oh i love a bit of good weather watchin i do