WINTER 2007-8
part 6: Significant windstorm, March 10th 2008? The outcome.
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After writing up the
Sunday 9th of March update in the lead-up to the storm I headed over to
Borth for low tide, the aim being to get a few photos of the "Fossil
Forest" since the light was especially good. It was a beautiful
afternoon down there with the peat-beds and stumps well-exposed between
Borth and Ynyslas:
However,
not long after arriving there a cloud that had been building up over
the bay moved over me and gave a short downpour of heavy rain and
little hailstones. I was thoroughly drenched and the cameras went
quickly back into the bag. But afterwards, the sun came out and the
reflections on the rain-drenched sand were beautiful:
....and as the water drained away, ripple-marks on the sand made
eyecatching patterns:
Just
twelve hours later the storm would be moving in!
I got up just before 0300 on Monday 10th March with heavy rain and
gusty winds lashing the street outside. Observations and travel reports
confirmed the worst of these winds were hitting southern areas with an
82mph gust recorded at Mumbles in South Wales and roads blocked by
fallen trees in most counties south of a line from Fishguard to Dover.
The low was crossing central Ireland and, with again a slightly more
southern track, its centre was heading straight towards Mid-Wales.
The winds
accompanying the cold front eased by first light and I got ready to
head to Aberystwyth,
leaving just before 0730 with a view to avoid the morning traffic which
can be bad. By 0800 I was set up in a layby looking NW over the Harbour
and its outer breakwaters. Although the wind had dropped to just a
force 4-5, the ground-swell was big and I became absorbed in shooting
images of the huge waves that were breaking over the end of the Prom:
As high
water approached, the Prom became deserted as the police wisely
closed it. The tide rose and rose until it was less than a foot off the
top of the Town Quay whilst water cascaded over the Prom into the
Harbour:
Note the
red boat below - and then again in the next image...
The unusual water height in the Harbour is evidence for the storm-surge
that
accompanied this system. A storm-surge is basically an extensive bulge
of water that forms offshore under the centre of a cyclonic storm,
whether tropical or extratropical. Water-levels in this bulge are built
up by two factors - sustained strong winds and the low air pressure.
They can result in higher-than-usual tides especially if the timing of
the low pressure system moving through and high tide are coincidental.
I then headed out of Aberystwyth to Borth,
finding a couple of vantage
points below the War Memorial on Borth Head that faced north - away
from the heavy rain showers that were
getting going again. Again the scene was spectacular, but because I was
some
distance away, the shots needed a telephoto lens:
What was weird was the lack of wind as the centre of the low started to
move in! The sea had an unruffled appearance but huge rollers were
breaking against the sea-defences. Imagine if there had been a force 11
gale behind these waves, as there would have been had last Thursday's
GFS forecast runs been correct with the low tracking much further
north! Severe structural damage and flooding would almost certainly
have resulted.
I left
Borth and headed home, stopping on the way to photograph the
Leri estuary and then the Dyfi
at Glandyfi. Both had extremely high
water levels, not far off those seen in the Burns' Day Storm. The Leri
is in the photograph below: it is contained in a levee-like embankment
here and the water level is a good couple of metres above the land
around, out of sight to the L of the field of view. The crossing in the
distance is the Cambrian Coast line. Some years ago, the LH bank here
breached, causing extensive flooding.
After
getting some food down me I headed back out to the coast at
lunchtime and, on the hills above Borth, basked in warm sunshine with
blue skies overhead and absolute calm, despite the angry-looking dark
grey shower clouds that occupied the sky in all directions. This really
was the "eye of the storm" - not a true eye as hurricanes have, but the
calm conditions indicated I was very close to the centre of the low.
Back in
Aber, the Prom was open and I had a drive along it:
Some debris but I have seen a lot worse! Another storm of almost comparable
strength went on to affect more northern areas of
England and Wales and S Scotland/Northern Ireland overnight on Tuesday
11th and into
Wednesday 12th March, but the tidal cycle had peaked and the severe
damage threat to coastal communities had receded. No comfort, however,
to the molluscan inhabitants of the underwater sandbanks off Borth
Beach, as I found on a beachcombing trip on the following Thursday:
Hundreds
of bivalves had been ripped up out of their seabed burrows and were
strewn all over the beach, particularly these sand-gapers (Mya sp.) and
the more rounded Arctica (pretty much in the middle of the above pic). Here's a close-up showing
their shells broken or damaged in many cases....
Seabirds were there
in droves, tearing into the defenceless clams. By the time I arrived
hundreds had been eaten or part-eaten (below) but I rescued a few for
the freezer (they make
good baits for bass) - share & share alike!
The
flotsam that came ashore
was staggering and unfortunately most of it was smashed although I
picked out a couple of serviceable fish-boxes (below) and even found a
fishing-rod tangled in a mass of old netting - apart from needing a
couple of rings it appears to be serviceable!
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In the
aftermath of these storms, I mused on what a close escape this had
been. If the original,
more developmental scenario as
suggested by the GFS on Thursday 6th
March:
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had occurred, with the centre of the Low much further north, that
abnormal high tide would have been accompanied by severe gale or
storm-force westerly winds. The result would have been utter chaos,
with major flooding of low-lying coastal communities in Mid-Wales.
Watching how the
forecast models have handled this storm has been a
fascinating exercise. Small changes in upper air patterns affected the
low's timing, the point at which it started to fill and its track. All
were predicted fairly well: by Sunday it was clear that what actually
happened on Monday was pretty much going to happen. The significant coastal
flooding was restricted mostly to SW England and the Channel Islands.
I hope these two pages serve to demonstrate how weather forecasts
involving severe
storms evolve in the days that lead up to the event. Forecasting
involves applying scientific principles to a natural system in which
many variables are intereacting to produce the final outcome. Often,
these variables can fluctuate in a subtle manner independantly of one
another, but these subtle fluctuations can have a significant effect on
that outcome. The charts produced by each successive run of model
output reflect attempts to address how such variables are interacting:
in turn this explains why forecasts are updated on a daily basis, any
why anybody doing activities that are weather-dependant has to follow
these updates carefully in order to obtain an accurate picture of what
is going to happen.
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