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

19 October 2014

Bob Blog issued 19 Oct 2014

WEATHERGRAM
YOTREPS
Issued 19 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.

Background influences
The Atmosphere: The Southern Oscillation Index SOI (30 day running mean)
sums up the weather pattern over the South Pacific as one number. It is
based on the standardised difference in the barometer readings between
Tahiti and Darwin.
It has been negative since July and was near to -10 (Australian units)
during September but is now less extreme indicating that the recent trend
towards an El Nino is relaxing.

TROPICAL TOPICS
Tropical cyclone activity at present includes GONZOLA (after its direct hit
with Bermuda) heading for Scotland, and ANA going north to west of Hawaii.
The remains of HUDHUD over India last week caused a storm that brought
unseasonal blizzards to the Himalayas killing more than twenty trampers.

WEATHER ZONES

SPCZ=South Pacific Convergence zone.
SPCZ is expected to strengthen this week and to slowly spread south onto
Fiji from Tuesday, and possibly onto northern Vanuatu and Tonga on Sat/sun
25/26 Oct.
The week starts with a frontal zone attached to a deep low near 30S 155W
(low traveling south), and the north end of this is expected to move east
across French Polynesia FP, turning into a convergence zone over southern FP
by the end of the week.

STR= Sub-tropical Ridge
High over Tasmania on Monday is expected to travel NE across the Tasman Sea
and fade near Norfolk by Friday. Another HIGH is expected to travel south
of 45S past south of Tasmania on Thursday and then travel NE across central
or northern NZ on Sat/Sun 25/26, followed by a trough over northern NZ on
Monday and then a SW flow on Tuesday.

Between the tropics and NZ
Vessels in the All Points Rally are busy preparing for their trip to NZ from
Tonga, Fiji, or Vanuatu, to Opua. This rally (http://www.
islandcruising.co.nz/?page_id=1687) 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 is expected to travel south on Fiji from Tuesday and then onto northern
Vanuatu and Tonga around 25/26. Better to depart when the SPCZ is NOT
around.
The second restraint on a weather window is to pick an ETA over northern
NZ that does NOT have strong adverse winds. The table below is a spot
read out for Cape Reinga over northern NZ and things looks good this coming
week except for a passing front on local Tuesday morning around 20
1800UTC. Note that the next front is expected on Mon 27 Oct followed by
SW winds on 28th, so try and reach 30S on 28 Oct and that way you should
avoid the most adverse parts of that front.
CAPE REINGA
UTC |hPa |dir kt | m| %
20-Oct-14 0000|1019|234|13|2.2|0
20-Oct-14 0300|1019|222|14|2.2|1
20-Oct-14 0600|1018|215|18|2.2|2
20-Oct-14 0900|1018|230|15|2.2|3
20-Oct-14 1200|1019|247|16|2.1|5
20-Oct-14 1500|1019|247|19|2.1|39
20-Oct-14 1800|1019|206|22|2.3|74
21-Oct-14 0000|1021|198|20|2.6|54
21-Oct-14 0600|1021|185|21|3.0|21
21-Oct-14 1200|1023|162|15|3.1|21
21-Oct-14 1800|1022|147|13|3.0|23
22-Oct-14 0000|1023|145|08|2.9|23
22-Oct-14 0600|1022|147|06|2.8|7
22-Oct-14 1200|1023|117|03|2.8|2
22-Oct-14 1800|1022|100|03|2.8|47
23-Oct-14 0000|1021|073|02|2.7|76
23-Oct-14 0600|1020|227|03|2.5|68
23-Oct-14 1200|1019|248|06|2.4|60
23-Oct-14 1800|1019|226|11|2.3|53
24-Oct-14 0000|1019|216|13|2.1|45
24-Oct-14 0600|1019|208|12|2.0|70
24-Oct-14 1200|1020|201|09|2.0|94
24-Oct-14 1800|1020|233|10|1.9|78
25-Oct-14 0000|1020|222|10|2.0|61
25-Oct-14 0600|1021|195|10|2.1|31
25-Oct-14 1200|1022|171|09|2.1|1
25-Oct-14 1800|1022|160|05|2.1|1
26-Oct-14 0000|1022|182|05|2.0|2
Spot read out at Cape Reinga; hPa is air pressure, Dir kt is wind
direction true and speed in knots, m is wave height in significant metres,
% is cloud cover The next timing constraint is the middle part. This week
(for sail boats) it is to try and avoid the light variable winds that belong
to the centre of passing Highs in the STR. This is difficult when the STR
is strong and placed across the middle of the route. May be better to wait a
week or two for more wind.
Those who intend to go to North Minerva and wait there for a good sailing
window are likely to have an OK wait this coming week-nothing uncomfortable
is expected at Minerva:
MINERVA REEF
UTC | hPa |Dir kt| m | %
20-Oct-14 0000|1016|089|04|2.5|85
20-Oct-14 0300|1016|117|03|2.5|87
20-Oct-14 0600|1015|144|02|2.5|89
20-Oct-14 0900|1015|163|03|2.4|65
20-Oct-14 1200|1016|170|03|2.4|41
20-Oct-14 1500|1016|180|04|2.4|36
20-Oct-14 1800|1016|164|06|2.3|31
21-Oct-14 0000|1016|140|06|2.2|52
21-Oct-14 0600|1016|139|09|2.1|7
21-Oct-14 1200|1016|137|09|2.0|43
21-Oct-14 1800|1016|139|10|1.9|83
22-Oct-14 0000|1016|133|12|1.9|99
22-Oct-14 0600|1016|133|14|1.8|97
22-Oct-14 1200|1017|123|12|1.8|63
22-Oct-14 1800|1017|126|13|1.7|25
23-Oct-14 0000|1016|103|11|1.8|32
23-Oct-14 0600|1016|102|12|1.9|46
23-Oct-14 1200|1016|084|10|2.0|60
23-Oct-14 1800|1015|096|08|2.0|73
24-Oct-14 0000|1015|114|09|2.0|85
24-Oct-14 0600|1015|113|12|1.9|61
24-Oct-14 1200|1015|109|10|1.9|36
24-Oct-14 1800|1015|121|11|1.8|66
25-Oct-14 0000|1015|124|13|1.7|96
25-Oct-14 0600|1015|120|16|1.7|98
25-Oct-14 1200|1015|113|15|1.7|99
25-Oct-14 1800|1016|118|16|1.8|92
26-Oct-14 0000|1016|123|16|1.8|84
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 The front that is expected to be crossing northern NZ on Tuesday is
likely to continue NE and peel off to the east across the Kermadecs on
Wednesday If already at Minerva then may as well wait until after this
front (as it is followed by southerly winds and swell) so wait until late
Wednesday or Thursday before proceeding from Minerva to NZ.

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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