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

03 November 2014

Bob Blog extra

WEATHERGRAM
YOTREPS
Issued 04 November 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 Special edition aimed at those at the Minerva Reef yacht
club

DEPART BEFORE 1pm WEDNESDAY

This morning most (not all) computer models are picking that a tropical
trough may trigger the development of a low near 25S 175E ( south of
Fiji) on Sunday 9 Nov, and this low may then travel east for a few days
pushing a front with strong to gale NE winds over Minerva by late Sunday and
forming a squash zone of easterly gales near 30S 18 on Sunday/Monday.

This scenario still has only around 66% chance of actually happening, but
its likely impact is worth avoiding. To do so , anyone at Minerva should
depart for NZ by around noon Wednesday ( and those in Tonga should now stay,
or , if they depart today , brace for strong easterly winds near 31S on
Sunday /Sunday night.

NOTE that if this feature does NOT form, then the waypoint given in the
forecast below will still work OK, but winds near NZ will be westerly rather
than easterly.

===================================================
Here is a voyage forecast for any yachts in Minerva with a cruising speed or
around 6 knots, departing for North Minerva on 1pm Wednesday
(050000UTC) and heading for Opua.

DISCLAIMER: weather is a mix of pattern and chaos. The real world unravels
away from the model output shown here. Computer data does NOT do well near a
coast or in a trough. In a convergence zone computer gives averaged-out
light winds, but occasional squalls can deliver 30 knots for
30 minutes. If your baro strays away from target pressure more than 5 hPa
the forecast needs updating.

DECODE: Time HH:MM is hours and minutes in UTC. Lat and Long are in degrees
and minutes. hPa is barometer in hPa, Wind is compass octant coming FROM and
lull~avg~gust is speed range in knots. Crs-Bsp is boat course to in degrees
TRUE and speed in knots. TWA is the angle between the wind and the boat
course, minus for wind on port. Waves are significant wave height in
metres=average of top third, or are exceeded around once in 7 waves or once
a minute. Add 50% to get the occasional wave which occurs or is exceeded
around once every 10 minutes.

Table is in UTC and degrees True

Head off along 220 True to 29S 176E , to get ready for ESE winds near NZ.
Timestamp | POSITION | Air | WIND | BOAT
|waves
UTC- HH:MM|----Lat:/ Long----:| hPa | lull~avg~gust |Crs-Kt|TWA|Sig~ocnl
05-Nov-00:00|23:37S/178:58W|1017|ENE11~14~21|219-06|-154|2.0~3.0m
05-Nov-04:15|23:57S/179:16W|1016|ENE09~11~17|219-06|-148|2.3~3.4m
05-Nov-08:30|24:18S/179:34W|1018|ENE10~13~19|219-06|-151|2.3~3.4m
05-Nov-12:43|24:38S/179:52W|1017|-NE10~13~19|219-06.1|-164|2.2~3.2m
05-Nov-17:01|24:58S/179:49E|1016|-NE09~11~17|219-05.9|-170|2.1~3.1m
05-Nov-21:24|25:19S/179:31E|1017|-NE09~11~17|220-06.0|-175|2.0~3.0m
gybe
06-Nov-01:56|25:39S/179:12E|1016|NNE06~08~12|220-06|152|1.9-2.8m*
06-Nov-06:47|25:59S/178:54E|1018|NNW02~02~03|220-05|109|1.8-2.7m*
around here we encounter the north end of a passing front- kills the wind,
maybe some drizzle, then new wind from DE, keep going along 220 true
06-Nov-12:05|26:20S/178:35E|1019|SSE05~07~10|220-05|-64|1.7-2.6m**
06-Nov-17:17|26:40S/178:16E|1018|-SE11~14~21|220-05.3|-81|1.7~2.6m
06-Nov-22:01|26:59S/177:57E|1020|-SE14~18~27|220-05.6|-83|1.7~2.6m
07-Nov-02:33|27:20S/177:38E|1019|-SE14~18~27|220-05.6|-81|1.6~2.4m
07-Nov-07:05|27:40S/177:18E|1020|ESE13~16~24|220-05.7|-99|1.5~2.3m
07-Nov-11:38|28:00S/176:59E|1021|ESE12~14~22|221-05.9|-111|1.4~2.2m
07-Nov-16:03|28:20S/176:39E|1020|ESE13~17~25|221-06.2|-116|1.4~2.0m
07-Nov-20:14|28:40S/176:20E|1020|-E-13~17~25|221-06.4|-125|1.4~2.2m
once winds turn E we can go direct
08-Nov-00:22|29:00S/176:00E|1019|-E-12~16~23|194-05.7|-97|1.4~2.0m
08-Nov-06:04|29:31S/175:51E|1019|-E-13~17~25|194-05.9|-101|1.4~2.0m
08-Nov-11:25|30:02S/175:43E|1019|-E-15~18~27|194-06.1|-107|1.4~2.0m
08-Nov-16:33|30:34S/175:34E|1018|-E-14~18~27|194-06.0|-103|1.4~2.0m
08-Nov-21:39|31:05S/175:25E|1019|-E-17~21~32|194-06.1|-102|1.5~2.3m
09-Nov-02:44|31:36S/175:16E|1017|-E-16~20~30|194-06.2|-105|1.6~2.4m
09-Nov-07:54|32:07S/175:06E|1019|-E-16~20~29|194-06.0|-98|1.6~2.4m
09-Nov-13:15|32:38S/174:57E|1018|ESE16~19~29|194-05.8|-87|1.6~2.4m
09-Nov-18:38|33:09S/174:48E|1019|-E-16~20~29|194-05.9|-92|1.6~2.4m
10-Nov-00:18|33:41S/174:38E|1020|ESE14~17~26|194-05.6|-88|1.6~2.4m
10-Nov-06:05|34:12S/174:29E|1019|ESE12~15~23|194-05.5|-90|1.5~2.3m
10-Nov-11:58|34:43S/174:19E|1020|ESE10~12~18|195-05.4|-90|1.4~2.0m
10-Nov-18:08|35:14S/174:09E|1019|ESE08~10~15|ETA off Opua around 8am local
Route distance 807.31nm| route time 5d 18h 08m|||
*= motoring with light winds **= motoring into the wind, or fall off for
comfort but that will take longer.
SWELL : From east until 25S, then from SW until 29S , then from S until
30S, then from SE until 32S then from East/ENE.

Updates from ZKLF Radio fax on 3247.4, 5807, 9459, 13550.5 or 16340.1 kHz Or
HIGH SEAS on ZLM 6224 kHz and 12356 kHz at 0303Z, 0903Z, 1503Z and 2103Z and
on 8297 kHz and 16531 kHz at 0333Z,1003Z,1533Z and 2203Z or, for warnings,
send email to query@saildocs.com, No subject, saying SEND
http://m.metservice.com/warnings/marine
Or SEND http://www.met.gov.fj/aifs_prods/10140.txt
or let me know at bob@metbob.com or TXT/PHN to +6427 776 2212

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