Weather Briefing
Spindrift
David Hersey
Mon 25 Feb 2008 00:31
received prior to departure across The Drake:
Hi David
The outlook has inmproved since I last sent you an indication of the
weather
for your passage.
Current Situation and Synoptic Outlook
At present there is a fairly stationary low centred at 70S 100W. The centre
of this low will fill gradually and combine with another low further west,
currently centred at 69S 125W. The movement and development of this low are
the
main factors influencing your weather
A low south east of you will move east which, when taking into account the
movement of the low above, enable a ridge of high pressure to develope along
your track tomorrow morning.
Through Monday 25th, the primary low will be slow moving, principly being
blocked by a high pressure ares off south east Argentina. By midnight
tomorrow
the low will be centred at 60S 108W and the high pressure ridge will move
slightly east.
During Tuesday 26th the ridge of high pressure is expected to move north
east slowly which will allow a weak trough to develop from the primary low
into
the Drakes Passage.. This feature is often poorly moddled by the weather
computers and may not happen. However, in the event that the synoptic
situation
develops as expected, the weak trough will produce E winds in the southern
half
of the Passage with W winds in the northern half and a light variable zone
in the middle.
This trough is likely to develop into a secondary low which will move
eastwards through the Drake on Wednesday 27th. At this time the primary low
will
still be slow moving, centred at 57S 103W. After the secondary low passes
there
will be a period of light winds followed by N winds filling in from the
west,
associated with the primary low. Thus if you are east of your rhumb line at
this point, the N winds will reach you later.
Thursday 28th sees the primary low starting to move toward the Drake but
still slow moving. The low has all the appearances of being hampered by the
Andes from moving east (usually know as 'coastally trapped') added to which
the
high pressure off Argentina is also blocking the low's progress.
However, the systems are moving slowly east and on Friday 29th this will
produce strong N winds on the track. I hope you will be in by then.
Routing
In general terms follow the rhumb line, but if anything err toward the
eastern side. Not only will this give more benign conditions for longer, but
you
will also be better placed fo the NE winds in the latter stages of your
passage.
Wind forecast
Starting SW F3 or less at 1000 UTC on 25th veering steadily to be W F3 by
2000 UTC. Position at midnight 25th 62 44S 063 54W.
Through the night the wind continuing to veer, remaining light, to be N F3
or less by 2000 UTC on 26th. Position at midnight 26th 60 40S 065 04W.
The wind will continue to veer becoming E F3 by 0200 UTC on 27th and SW F3
by 0700 UTC. After that the wind should increase fairly quickly to SW F5
possibly F6 or & for a short period before veering again and reducing W F4
by 1600
UTC. Note that this will happen later if you are east of your position
above. After a light patch early evening, the wind will have veered NE F4 or
5 by
midnight. Position midnight 27th 57 47S 065 00W.
Soon after midnight the wind will start backing slowly to be N F4 or 5 by
0700 UTC, veering and dropping NW F4 before veering agian from 1400 UTC to
become N F4. Position midnight 28th 55 20S 066 49W.
I expect you to arrive early on Friday, before the winds increase above N
F5
fater 1000 UTC.
If you send me your position each day (say 1200 UTC) I can let you have a
quick update on current weather and developments.
Regards and have a safe passage.
Anthony