Weather or not?
Rhiann Marie - Round the World
Stewart Graham
Tue 10 Nov 2009 10:34
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Now the serious countdown starts to the off for the
Atlantic leg of this adventure. There are a few things that will determine the
date for the departure. Number one we have a number of family and crew arriving
who are joining for the crossing and they are arriving Friday and Saturday, so
it would be bad manners to go before then - though sailing alone is wonderful
and its always an option if the rest find me too hard going....
On the other hand Gran Canaria is chock-a-block
with boats and I am existing in a begged/stole/borrowed berth to await the
arrival of people from Discovery yachts to do a few wee bits and pieces this
week, and off course crew flights are already arranged to come here. So at the
moment I have the berth till the 13th. I would like it until the 16th so I can
get everyone aboard and basic familiarisation of the boat and safety briefings
done for the two new crew (uncles) and brushing up and review of progress to
date with established crew. Alternatively if we have to move on the 13th then we
will try to get another berth in Gran Canaria (all chocka block) , anchor (chock
a block and poor) or move to another island and the guys will have to catch
us up. So ideally I would like to leave for the transocean on the 16th and
ideally I would like to have a crew. Watch this berth!
So while I hone my grovelling, charming and
negotiating skills to maintain a berth for the rest of the week there is the
small issue of the weather to consider. The Hurricane season has in the past
been considered to have ended at the end of October. Our experiences in the
Caribbean has told us that in more recent years people have said that they
gradually see the end of the season creeping into November.
What happens with hurricanes is that "tropical
waves" small perhaps intense fronts form off the Cape Verdes and travel across
the atlantic with the prevailing gradient winds towards the Caribbean sometimes
disipating and sometimes deepening and strengthening in extreme cases into
Tropical Storms or even Hurricanes. This tends to happen over the course of
the hotter months of the year when the seawater has also has had time
to heat up to around 25 - 26deg C ( remember we are still in the Northern
Hemisphere - so June to October) with a few in the shoulder months of May but
more notably November.
While we would like a strong breeze or near
gale, anywhere between 20 - 30 knots, providing it is from the right direction -
over our quarter - we would prefer not to have a storm or a
hurricane! So looking at the statistics I see that there have been 571
Tropical Storms over the 56 years from 1944 to 2000, of which 337 have developed
into hurricanes. Notably in September, October and November over 60% of these
storms have developed into hurricanes. I believe this is due to the
build up of sea temperatures as the months go on. Of the total
occurrences of 471 tropical storms over these 56 years however only 26
formed in November and only 16 of these in November, so an average of less
than 0.3 per year and looking through the statistics it would be logical to
assume most of these occur in the earlier parts of the month.
Unfortunately I did not start sailing until 2001
and I dont have any statistics from then just snipits that in 2003 two tropical
storms developed in December, anyway this is now and we have good equipment to
get weather forecasts. We can get grib files over satellite for seven days
forward and this should give us enough warning of extreme weather to sail out of
the way of it. I have also been watching the weather for the past month and I
have been seeing a series of tropical waves developing around cape verde and
tracking across but not really come to anything. They seem to have disappeared
for the next week. I will check again tomorrow. It also seems that the trade
wind direction is settling in but I would prefer to see them more established
and a little stronger for our departure.
We have the choice to go the direct and more
northerly route from Canary Islands to the Lesser Antilles. However we will not
as this will mean that we gamble with weather and will certainly be higher than
the trade winds but more importantly it keeps us tracking north of where the
tropical waves or storms might form and they in turn tend to track west and
north which would be across our path. Also it means that should we have any
problems in the first thousand miles we eliminate the option of bolting for Cape
Verde, and finally we lose the great advantage of stronger equatorial west going
currents further south.
The South route " head south till the butter melts
and turn right" would take us by the NW side of the Cape Verdes before turning
right and west to pick up the trades and the stronger currents. The challenge
will be when to turn right but we will try to hold out for stronger trades to
avoid the frustration of lighter winds and weaker currents but we will monitor
the weather daily and make the decision. We should try to get to 20N at about
25W but we will see if the itchy trigger finger can remain under control long
enough to get south. Passage distance is probably around 3000 miles and we hope
for an 18 day passage time. Depending on winds that could be 21 days but we
would be disappointed with a slower time than that, despite the comfort aboard.
Chi sinn!
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