Hurricanes

[Selina]

I'm a real novice at all this so please be gentle with me!

I've got a really bizarre question:

I've heard many times that Britain gets the "tail end" of hurricanes a few days after they've happened, if they track in the right direction obviously. Is this true? And if so, and I'm really sorry if this has been asked before, then how come they don't build back their strength when coming back across the Atlantic?

And this leads on to my next question, does anyone have evidence or information that backs that the "hurricane" in the 80's was actually a hurricane? I watched the programme when it was on where they were talking about what happened and that it was just a really bad storm, but then there are the people that still stand by the fact that it was hurricane, and was wondering what people on here think and if it WAS a hurricane then how come it happened and if it can how come we don't get more of them or does it just depend on the storm's journey across the Atlantic?

Thanks for listening and sorry again if these questions have been posted before!

Thanks

Selina

[Greyowl]

The winds in 1987 were Hurricane force cat3 but not a Hurricane.

This article on WIKI will give you some more info.

http://en.wikipedia.org/wiki/Great_Storm_of_1987

[Coast]

Had a quick trawl of the net as I wasn't certain either. Hurricanes being from warmer climes, don't as such make it to these shores but this paragraph gives some clues as to what we might expect:

'Some hurricanes, however, veer back out into the Atlantic. The cooler northern waters cannot sustain a hurricane and so it rapidly weakens to become an Atlantic cyclone - like the dozens of windy, rainy depressions we see in the UK every year in many ways. The difference however is the amount of warm, moist air still entrapped. Hence the very heavy rainfall that the remains of such systems can bring along with them'

Source: http://www.geologywales.co.uk/storms/hurricanes.htm

The Met Office say:

Strictly speaking, tropical cyclones do not occur over the British Isles. However, we are sometimes affected by deep depressions that are the remnants of tropical cyclones. Intense mid-latitude depressions, even those which do not originate from a tropical cyclone can produce winds of a strength equivalent to a tropical cyclone.

Source: http://www.metoffice.gov.uk/education/seco...l_cyclones.html

[Jack Wales]

Yes we do get the tail end of hurricanes, so in a nutshell...

Atlantic hurricanes form in the tropics and generally head east to west across the Atlantic towards the USA/Caribbean under the mid Atlantic ridge. As they reach the western side of the tropical Atlantic sometimes they curve northwards skimming or missing the US Eastern Seaboard. By this point the hurricanes are over coolers seas so are unable to maintain their energy levels plus they also tend to merge with frontal systems and get picked up by the Polar Jet stream sending them back on a westward course towards us. Although by this point the hurricanes have turned extra-tropical (lost their tropical characteristics i.e. eye-wall, warm core et al) they can still develop into potent low pressure systems.

As for October 1987, this was not a hurricane in any way shape or form, the winds were not hurricane strength (sustained at 74mph for over a minute). In fact Britain is exposed to strong winds regularly during Autumn/Winter equal to the 1987 event however such synoptics normally hit the west/north where the landscape is more attuned to such conditions or it is deemed less newsworthy.

[Radiating Dendrite]

Hurricanes form in the tropics and gather their energy from the warm seas (27 degrees and warmer) that they travel over (between 5 - 30 degrees north and south of the equator, except in the S. Atlantic where they do not form). They have a warm core and need a relatively stable atmosphere (moist and with low wind shear) in which to grow and survive.

Once they move out of this trpical zone (i.e. into the North Atlantic) they loose their energy source (the warmth of the sea) and atmospheric conditions become too unstable for them to maintain their form and tropical origins.

They then become extra tropical and their remenants can go on to merge with low pressure systems (which have cold cores) that can effect the UK.

[Greyowl]

From the MET Office website.

It's worthwhile to consider whether or not the storm was, in any sense, a hurricane - the description applied to it by so many people.

In the Beaufort scale of wind force, Hurricane Force (Force 12) is defined as a wind of 64 knots or more, sustained over a period of at least 10 minutes. Gusts, which are comparatively short-lived (but cause much of the destruction) are not taken into account. By this definition, Hurricane Force winds occurred locally but were not widespread.

The highest hourly-mean speed recorded in the UK was 75 knots, at the Royal Sovereign Lighthouse. Winds reached Force 11 (56-63 knots) in many coastal regions of south-east England. Inland, however, their strength was considerably less. At the London Weather Centre, for example, the mean wind speed did not exceed 44 knots (Force 9). At Gatwick Airport, it never exceeded 34 knots. Force 8.

The Great Storm of 1987 did not originate in the tropics and was not, by any definition, a hurricane - but it was certainly exceptional.

75Knts = 86.4 mph

[SnowBear]

It is worth while reflecting for a minute here on true hurricanes while we are on the subject.

As GreyOwl's post says above, in the 1987 storm (which I remember very well and yes it was a case of "ne'er known a night like it"!) we had winds of approx. 85mph sustained winds.

A Cat5 hurricane in the tropics can have winds sustained of 155mph or higher with gusts a good deal higher closing on 200mph. Well over double the speed of the 1987 storm we had here.

I seem to remember somewhere when assessing damage for hurricanes that the damage caused by a hurricane as it increases in strength increases exponentially. The wind pressure on say a blank brick wall increases four fold in relation to the air speed. I think this is right, someone else please do correct if it is not. So this means that a Cat5 hurricane is vastly larger in strength than say a Cat3, which is why hurricanes such as Katrina, where Cat5 was reached, even the drop to a Cat4 and Cat3 statuses as it made landfall made a lot of difference to the damage on land. If it was a full Cat5 when it made landfall and moved onshore the damage we saw would have been immensely more, probably to the point of New Orleans wiped off the map completely.

So yes we had our "hurricane" although not in the strictest of terms, lets just be glad we do not have the real thing on these shores! lol

[Selina]

Thank you all very much for your replies!

[Gray-Wolf]

And what of the 'hybrids' that we were treated to a few years back?. As the planet warms are we ever more likely to cop for a north tracking hybrid?

[smich]

And what of the 'hybrids' that we were treated to a few years back?. As the planet warms are we ever more likely to cop for a north tracking hybrid?

Yes GW, the most interesting of which, would perhaps be Vince in October 2005, which never headed West atall!

Steve M

[Roger J Smith]

Hurricane Debbie tracked from the Azores to a point near Donegal on 16 September 1961 and then merged with a deep low which had been moving slowly east to the south of Iceland. This storm is shown in the official storm tracks as a hurricane right to the point where it moves north of Ireland on the 16th. Whether this is an error by NOAA or the official decision on this storm, I am not certain. However, I did read somewhere that this storm was strong enough to produce wind gusts over 100 mph in Northern Ireland where damage included tearing the roof off a school building.

So this would appear to be the one case where a North Atlantic hurricane reached any part of the British Isles and the U.K. in particular before going extra-tropical. That normally happens after about a day over sub-25 C ocean temperatures, or two days in extreme cases.

This storm is not well depicted on the wetterzentrale archive maps, in fact it must have been a marginal hurricane that ran along a cold front associated with the deeper low. It only shows up as a separate feature on these maps on the 15th but the NOAA track matches the wave shown on the front, only there must have been 20-30 mbs of low pressure not analyzed on these maps on the 13th and 14th.

A hurricane remnant also caused severe damage (including losses to the fishing fleet near shore) to western Ireland in the autumn of 1927 according to some historical records I was reading on another forum.

[Radiating Dendrite]

Found this about Hurricane Faith (1966):

"When the storm passed Newfoundland, not only was it still a tropical system, it was still a Category 2 hurricane. Faith struck the Faroe Islands on September 5 with sustained winds still over 100 mph and only then did the storm cease to be a tropical system. The new extratropical storm went on to strike Norway with winds as high as 60 mph. Faith weakened to an extratropical depression over Scandinavia and was tracked over Russia, later degenerating into an extratropical low and swerving north".

Taken from Wikipedia lol, but they do have a great deal of information when it comes to Hurricanes and different seasons in particular!

[Somerset Squall]

Found this about Hurricane Faith (1966):

"When the storm passed Newfoundland, not only was it still a tropical system, it was still a Category 2 hurricane. Faith struck the Faroe Islands on September 5 with sustained winds still over 100 mph and only then did the storm cease to be a tropical system. The new extratropical storm went on to strike Norway with winds as high as 60 mph. Faith weakened to an extratropical depression over Scandinavia and was tracked over Russia, later degenerating into an extratropical low and swerving north".

Taken from Wikipedia lol, but they do have a great deal of information when it comes to Hurricanes and different seasons in particular!

Righty from the horses mouth, saying Faith was only declared extratropical near the Faroe Islands (north of Scotland):

http://www.nhc.noaa.gov/archive/storm_wall...6-prelim/faith/

Very interesting this one. However, it simply could be an error. We all know that technology was more primative back then but i agree it doesn't entirely explain why Faith was tracked as tropical that far north. No explanation is given.