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

27 August 2023

Bob Blog 27 Aug

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.
Compiled Sunday 27 August 2023

A BLUE PERIGIAN MOON
The full moon on Thursday 31 August is the second full moon this month.
Many think the second full moon in a calendar month is called a 'blue'
moon,
perhaps because that is the colour it was given in some calendar.
But further research, such as this article
skyandtelescope.org/observing/once-in-a-blue-moon/
reveals that the origin is obscure.
This full moon is also a SUPERMOON coinciding with the monthly perigee.
It will be ~360.000km from earth and it only gets this close around three
times per year.
Of course, a closer moon means more extreme tides (both low and high).
Also, there is a lag between the perigee and the largest "king tide" of few
days.

tides.niwa.co.nz shows the tide heights plus and minus a few weeks around
this full moon for Opua in NZ (a reasonably well-behaved tidal spot with a
range ~2m) and from Karori rock near Cook strait and near a tide nodal point
(Amphidromic point) with a tide range of less than a metre (see illustrated
edition).

In its State of the Climate in the South-West Pacific 2022 report, the World
Meteorological Organization (WMO) said water levels were rising about 4 mm
per year in some South Pacific areas, slightly above the global mean rate,
so those sailing around the South Pacific should be aware of the King tides
this coming weekend

TROPICS
It has been a busy week for cyclones and tropical depressions.
HILLARY swamped LA and SanDiego. HAROLD brought rain to southern Texas.
FRANKLIN brought heavy rain to Hispaniola.
EMILY and GERT had brief lives in the central North Atlantic. SAOLA visited
Philippines and DAMRAY affected Japan.

WEATHER ZONES
The South Pacific Convergence zone is expected to intensify this week
between Solomons and Vanuatu and drift south and form a LOW L1 near New
Caledonia by mid-week Wednesday. Fresh trade winds over Tonga and the Cooks.
A lingering lull about French Polynesia this week

HIGHS and LOWS
Low L1 near New Caledonia by mid-week expected to deepen and travel SE
towards northern NZ.
HIGH H1 1031 in South Tasman Sea travelling east across NZ mid-week. Avoid
squash zone between H1 and L1.
Low and trough L3 expected to travel NE from Southern Ocean to south Tasman
Sea by end of week.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more details about your voyage, then check metbob.com to
see what I offer.
Or Facebook at /www.facebook.com/metbobnz/
Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe
at bottom).
Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt +64 277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

20 August 2023

Bob Blog

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.

Compiled Sunday 20August 2023

How big is the HOLE this spring?

During the dark of winter chemicals build in the air above Antarctica. When
sunlight returns at the end of winter and start of spring, between August
and October, this triggers chemical reactions which delete the Ozone
concentration in the Stratosphere. During the second half of last century
CFC gases were used in refrigeration and as a spray can expellant and vented
into the atmosphere triggering depletion of ozone over Antarctica every
spring-a phenomenon called the OZONE HOLE.

Scientific study of this depletion in the 1960 to 1980s lead to WMO
declaring the Montreal protocol in 1987 to phase out CFC. This is a rare
treaty that achieved universal ratification. It has been considered as a
success for the UN, and a sign that humans can mitigate planetary pollution.

However, this month observations show an earlier than normal depletion in
Antarctic ozone. If this continues, we may have as big a hole as in the bad
years around 2000. This time it isn't CFC to blame. The theory is that it
may be due to extra water vapour and some other gases from the Hunga -Tonga
/Hunga Ha'apai Volcano in January 2022. The blast produced a sonic boom that
travelled several times around the planet and a plume that rose 58km into
the Mesosphere and threw "unprecedented" amounts of water vapor into the
stratosphere.

In August 2022, a NASA report stated, ".as detected by NASA's Microwave Limb
Sounder.. The excess water vapor injected (into the stratosphere) by the
Tonga volcano... could remain in the stratosphere for several years... would
have a small temporary warming effect.... would not be enough to noticeably
exacerbate climate change effects."

Maybe this water vapor has found time during winter to build in the
Antarctic. In the stratosphere it acts as a "greenhouse" gas and reflects
infrared radiation in all directions, with that directed downwards warming
the surface. Sunlight converts some of it into hydrogen oxide molecules and
these destroy ozone.

Ozone absorbs UV and uses this to warm the stratosphere. The main effect of
an ozone hole is an increase in UV reaching the earth's surface and
consequential sunburn. Less ozone also means less warming of the
stratosphere from sunlight. A cooler stratosphere strengthens the polar
vortex, affecting the surface weather.

A good parameter to check out the polar vortex is SAM (or its proxy AAO)
At present it is negative, and that is consistent with a weak polar vortex.
So we shall watch the trends and see what happens with the Ozone hole over
the next few months.

TROPICS
It has been a busy week for cyclones and tropical depressions.
LAN visited Honshu Island in Japan. GREG and FERNANDA travelled west across
the North Pacific. HILLARY is threatening southern California and there are
two, maybe three tropical depressions in the Atlantic.

WEATHER ZONES
The South Pacific Convergence zone is expected to have a quiet week across
the northern Coral Sea to Samoa. A showery trough lingers well south of
Society Islands. Another is expected to form over the Fiji area by mid-week
and then go east fand fade over Southern Cooks.

Apart from these troughs it looks to be a good week for sailing from Tahiti
to Tonga.

HIGHS and LOWS

Low L1 is expected to deepen to around 985 near Chathams on Monday and then
spin clockwise and then go southeast, feeding cold showery weather on
eastern NZ.

HIGH H1 should form in the north Tasman Se by mid-week then fade.

Another Low L2 from the south Tasman Sea is expected to bring unsettled
weather to NZ this weekend.

A good week for getting westwards across the Coral Sea and North Tasman Sea

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more details about your voyage, then check metbob.com to
see what I offer.
Or Facebook at /www.facebook.com/metbobnz/
Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe
at bottom).
Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt +64 277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

13 August 2023

Bob Blog

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.

Compiled Sunday 13 August 2023

Public Holidays
Sailors crossing the South Pacific are juggling their travel taking into
account factors such as the weather, and time out for tropical relaxation,
maintenance, and provisioning, plus the impending end of the cruising season
at end of October. 1 November is the nominal start of the cyclone season.

One factor that isn't usually taken int account, but can prove to be an
embarrassment or even a problem for newbies is the rather peculiar variation
in public holidays across the South Pacific

For example, tomorrow is a public holiday in Samoa for Father's Day, and
Tuesday is a public holiday in NEW CALEDONIA, FRENCH POLYNESIA and VANATU to
commemorate the Assumption of Mary. (Mary's assumption is also the patron of
Aotearoa /New Zealand, but not a public holiday there).

So, to help you plan voyaging between now and the end of the year here are
the public holidays across the South Pacific, from east to west and from
north to south

French Polynesia:
August 15 Assumption Day
November 1 All Saints' Day
November 11 Armistice Day
December 25 Christmas Day

Cooks :
26 October Gospel Day
25 December Christmas Day
26 December Boxing Day

Niue:
19 October Constitution Day
30 October Fourth Monday in October Peniamina Gospel Day
25 December Christmas Day
December Boxing Day

American Samoa
30 Nov (4th Thursday) Thanksgiving Day
25 December Christmas
26 December Family Day

Tonga
18 Sep Crown Prince's Birthday
6 Nov Tonga Day
4 Dec King Tupou I Day
25 Dec Christmas Day
26 Dec Boxing Day

Samoa
14 Aug Father's Day
9 Oct Lotu a Tamaiti (Day after white Sunday)
25 Dec Christmas Day
26 December Boxing Day

Fiji
7 September Constitution Day
Evg 26sep to evg 27sep Mawlid
10 October Fiji Day
13 November Diwali
25 December Christmas Day
26 December Boxing Day

New Zealand
23 October Labour Day
25 December Christmas Day
26 December Boxing day

Vanuatu
15 August Assumption Day
5 October Constitution day
29 November National Unity Day
25 December Christmas Day
26 December Family Day

New Caledonia
15 August Assumption day
24 September New Caledonia Day
1 November All Saint's Day
11 November Armistice Day
25 December Christmas Day

Australia observe Christmas and Boxing Days
Norfolk Island adds the following
9 Oct Norfolk Island Agricultural Show Day
29 Nov Thanksgiving Day (30 Nov in USA)

TROPICS
DORA stayed south of Hawaii but, in cahoots with a large HIGH at 30N,
brought a squash zone of enhance trade winds to Hawaii that fanned some
wildfires, bringing widespread death and destruction.
FERNANDA is now off the west of Mexico, and LAN is heading for Tokyo.

WEATHER ZONES
The South Pacific Convergence zone is expected to have a quiet week across
the Coral Sea to north of Fiji. A showery trough is expected to form over
the Fiji area by mid-week and then go southeast forming a new Low near 30S
south of southern Cooks by end of the week. Apart from this trough it looks
to be a good week for sailing from Tahiti to Tonga.

HIGHS and LOWS
There is a strong subtropical ridge along about 30 to 35S
HIGH H1 to north of NZ tonight is expected to travel steadily east to
southeast east of NZ.
Low L1 is somewhat blocked by a ring of high pressure all around and should
drift slowly to between Wallington and Chathams by mid-week, and then off to
the southeast.
HIGH H2 is expected to spread into western Tasman Sea by mid-week and then
travel northeast across NZ on Thursday and Friday, followed by another
trough from Saturday.
Nothing intense enough to consider avoiding this week. However, L1 over NZ
until Wednesday is bringing southerlies and cold rain., with often strong
winds around Cook Strait.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more details about your voyage, then check metbob.com to
see what I offer.
Or Facebook at /www.facebook.com/metbobnz/
Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe
at bottom).
Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt 64 277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

06 August 2023

Bob Blog 6 Aug

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.
Compiled Sunday 06 August 2023

SPCZ + Jetstream = wonky weather.
SPCZ, the south Pacific Convergence Zone is well known to Pacifica peoples.
It is where the easterly winds on the north side of the Easter Island High
bumps into the SE winds found on the north side of the Highs that migrate
across the Tasman Sea,
In previous blogs I've talked about how it has "moods" depending on things
like long term influences such as El Nino/La Nania, and the annual cycle,
and shorter cycles such as the MJO.
The recent weather over Vanuatu has been so wonky it prompted the request to
"explain the (for us) strange weather pattern that we experience now around
Vanuatu. It is not a ' normal' low, but what is it then?"

The surface map last Thursday shows a large 1039 High in the central Tasman
Sea and a zone of enhanced SE winds over Vanuatu. I call this a SQUASH ZONE.
The well-formed upper trough with Jetstreams is directly above the squash
zone and over Vanuatu. This helps cause strong upward motion leading to
squally weather. This upper trough has now deformed and Vanuatu weather is
now relaxing, The SPCZ stays lingering over northern Vanuatu much as it
usually does. It was the upper trough/Jetstream that produced the wonky
weather.

TROPICS
Former super typhoon DOKSURI brought the heaviest rain to east Chimba since
records began 140 years ago. Super Typhoon KHANUN followed and skirted
southern Japan. Cyclone and is now heading for Korea. DORA is travelling
west along 12N south of Hawaii, and EUGENE is travelling NW parallel to Baja
California coast. There is now high potential for development in the
Atlantic. As the old saying goes "July, stand by. August, a must".

WEATHER ZONES
The South Pacific Convergence zone is expected to have a quiet week across
the Coral Sea to north of Fiji. From the recent wonky weather over Vanuatu a
LOW L1 is forming near Fiji and expected to track to the SE and deepen. A
convergence zone is expected to linger between Northern Tonga and Austral
Island. It has some passing troughs, but these are mediocre, and weather
seems Ok for sailing from Tahiti to Tonga afterL1 has moved off. Northern
route avoids most of the convergence zone.

HIGHS and LOWS
There is a strong subtropical ridge along about 32S
Low to NE of Chathams Islands tonight is moving quickly off to the east and
High H1 should form east of NZ by mid-week.
Low L2 over southern NZ tonight is expected to travel NE and linger near
Chathams until Thursday, bringing a cold south/southwest flow to NZ.
After a ridge over NZ on Friday/Saturday the next trough is expected to
deepen into a slow-moving low over north Island early next week. Avoid.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more details about your voyage, then check metbob.com to
see what I offer.
Or Facebook at /www.facebook.com/metbobnz/
Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe
at bottom).
Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt 64 277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

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