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Bob McDavitt's ideas for sailing weather around the South pacific

26 October 2014

Bob Blog issued 26 Oct

WEATHERGRAM
YOTREPS
Issued 26 October 2014
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the
patterned world Coming Cyclone Season

NIWA has issued a Tropical Cyclone outlook for the coming South Pacific
cyclone season.
For the details go to (www.scoop.co.nz/stories/SC1410/S00048/southwest-
pacific-tropical-cyclone-outlook.htm
)
In summary NIWA expect the coming season to bring a near average number of
cyclones (8 to 12 in all), with the normal slow start, and February/March
peak.
VANUATU and NEW CALEDONIA are expected to have lower than normal risk.
A zone of slightly higher than normal risk is expected to stretch from
TUVALU across TOKELAU/SAMOA, to between NIUE and SOUTHERN COOKS. These are
expected to be only small variations from normal and so vigilance is
recommended.

Madden Julian Oscillation MJO
During the warmer months of the year we can anticipate phases of extra
convection in the South Pacific by watching the MJO. This index is NOT
having much impact on tropical convection during the coming week. My future
blogs will give more info about it.

TROPICAL TOPICS
Tropical cyclone activity at present includes ANA which has maintained its
integrity since re-curving wets of Hawaii early last week and is now
unravelling but its components may well reach the Victoria coast of CANADA
this week. There is also a feature currently name 04A FOUR in the Arabian
Sea.

Weekly rain maps show that there was heavier rain in the past week over
Solomons/ northern Coral Sea than in the previous week.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ strengthened in the past week but is expected to weaken and become more
spread out this week, mostly drifting north.

STR= Sub-tropical Ridge
High between Fiji and NZ today is expected to travel steadily eastwards
along 25 to 30S to 150W by Thursday and then to the southeast.
Another HIGH is expected to move form Aussie bight into Tasman Sea on
Wed/Thu and then eastwards along 30S on Fri/sat/sun. This makes for a
strong STR all week.
Another HIGH is in the south Tasman Sea tonight and expected to fade as it
crosses southern/central NZ on Monday. This high is just a break between
the troughs in the Southern Ocean and for the rest of the week the strong
disturbed westerly winds that are typical of spring dominate the Tasman
Sea/NZ pattern.
The ECMWF model (tinyurl.com/ecaus) shows that the STR is likely to spread
southwards on to NZ early next week (4 Nov).

Between the tropics and NZ :
Vessels in the All Points Rally (www.islandcruising.co.nz/?page_id=1687)
are looking for a good weather pattern for sailing to Opua, NZ from Tonga,
Fiji, or Vanuatu. This rally is free of charge (thanks to the sponsors) and
helps participants with planning, weather info, clearance, and seminars on
how to enjoy NZ. I shall do my bit here by commenting on windows of
weather to get to NZ.
The first factor to consider a departure date is the local weather: the
SPCZ does have some convective cloud over northern Vanuatu and parts of Fiji
at present but is not very intense and seems to be likely to drift north and
spread out. It isn't really strong enough to delay departure this week.
The second restraint on a weather window is to pick an ETA over northern
NZ that does NOT have strong adverse winds. Northern NZ is expected to
have strong winds from Monday to Thursday. Then these winds should ease
over the weekend 1-2 Nov and be light and variable early next week 3-4 Nov.
Arranging your trip to reach NZ on 3-4 and maybe 5 Nov looks OK at this
stage. Beyond that is too far away to tell at this stage.

The third factor is to avoid gales and heavy swells during the trip.
Sadly a burst of 3 to 4 metre swell from the southern Ocean moving as far
north as 23S by Friday in area north of NZ. This is in the STR and winds
will be light: no whitecaps, and the swells will have long periods of 11 to
12 seconds, so it is likely to be a gentle encounter. However it may
require a watchful hand on the tiller, and may be uncomfortable.
Anyone wish in avoid sailing in these condition should delay getting to 23S
until after Friday.
Those who intend to go to North Minerva and wait there for a good sailing
window are likely to have an OK wait until Thursday this week , then those 3
metre swells are expected to briefly reach the area (outside the
reef) on local Friday night (in time for Halloween) easing again on
Saturday.
MINERVA REEF
UTC | hPa |Dir kt| m | %
27-Oct-14 0000|1017|088|13|2.1|19
27-Oct-14 0300|1017|093|13|2.0|12
27-Oct-14 0600|1016|092|14|2.0|5
27-Oct-14 0900|1017|087|15|1.9|4
27-Oct-14 1200|1017|085|14|1.9|3
27-Oct-14 1500|1017|087|13|1.8|2
27-Oct-14 1800|1018|092|13|1.7|1
28-Oct-14 0000|1018|098|14|1.6|0
28-Oct-14 0600|1018|108|15|1.6|1
28-Oct-14 1200|1018|102|15|1.6|1
28-Oct-14 1800|1017|104|15|1.5|0
29-Oct-14 0000|1017|093|13|1.5|0
29-Oct-14 0600|1016|087|14|1.4|1
29-Oct-14 1200|1017|056|11|1.4|2
29-Oct-14 1800|1016|036|06|1.3|3
30-Oct-14 0000|1015|092|01|1.3|2
30-Oct-14 0600|1016|150|06|1.2|1
30-Oct-14 1200|1016|118|05|1.2|0
30-Oct-14 1800|1017|124|06|1.3|28
31-Oct-14 0000|1017|132|08|1.6|56
31-Oct-14 0600|1017|130|11|2.5|73
31-Oct-14 1200|1018|103|10|3.0|89
31-Oct-14 1800|1018|114|10|3.0|83
01-Nov-14 0000|1019|121|11|2.8|77
01-Nov-14 0600|1019|119|16|2.5|79
01-Nov-14 1200|1020|107|15|2.4|80
01-Nov-14 1800|1020|114|15|2.2|83
02-Nov-14 0000|1020|114|16|2.3|87
Spot read out at Minerva; hPa is air pressure, Dir kt is wind
direction true and speed in knots, m is wave height in significant metres,
% is cloud cover SO the decision about when to depart depends on these three
factors as well as speed of vessel and crew expectations, and the answer
will be
different for different vessels. Normally at this time of the year
there can be paralysis by over-analysis, especially at the Minerva yacht
club.
The good news is that there are NO gales expected to south of 30S after
Thursday- just that period of enlightened swells to factor in. Next week
could well be different.


See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom
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