Bob Blog 28 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 28 August 2022

Monsoon 2022

August rainfall in Pakistan has been between 2.5 and 5 times the 30years
norm, with a death toll currently around 937. At least 184,000 people have
been displaced to relief camps.


Why are they called hectoPascals?
Barometer is coined from Greek words, Baros for "weight" and metron for
"measure".

When the MKS system of units was drawn up in 1960 PASCAL was chosen for the
name for a unit of pressure (a Newton per square metre) as a commemoration
of Pascal's pressure experiment described below. And so, isobars are now
labelled in hectoPascals. The prefix of hecto is from the Greek word hekaton
for "hundred". So 1010hPa means 101,000 Pascals or 101,000 Newtons per
square metre- that's about a tonne per square metre , same as an elephant.
Yes, for a diver, that's the pressure exerted by about 32 feet or 10 metres
of (sea) water.

Pascal was a Frenchman and his experiment was conducted in 1648….

FRANCE, mid seventeenth century:

This was the time celebrated by Alex Dumas in the Three Musketeers. Louis
XIII was King, but the ominous Cardinal Richelieu was in charge, and did
things his way.

You may recall in my blog on 31 July
https://metbob.wordpress.com/2022/08/01/bob-blog-31-july/ I described how in
1642 Evangelista Torricelli, a student of Galileo, produced the first
barometer to make a vacuum. Now Marin Mersenne was a French Priest who
earned the title "the post box of Europe" for he travelled a lot, had many
contacts around the scientific word and was great at making connections. He
visited Italy in 1644 and Torricelli showed him the barometer. He returned
to Paris with a choice collection of writings, including Torricelli's paper.
These he shared in 1646 at the Paris Book Club that included Etienne and
Blaise Pascal.

Back story: Blaise Pascal was born in France in June 1623, the son of
Etienne Pascal, a lawyer. His mother died when he was three. He was educated
by his dad and proved to be a child prodigy in anything mathematical. At the
age of eight the family moved to Paris. When Blaise was 15 Cardinal
Richelieu (then Prime minister of France) imposed some harsh fiscal measures
which his dad opposed and for that had to go into hiding. The following year
his sister Jaqueline (then 17) appeared in a play given before Richelieu and
after a "fine performance" the Cardinal rewarded Jaqueline with a pardon for
Etinenne plus a job offer to the post of Tax collector for Rouen. Side note:
Jaqueline was a child prodigy writing a five-act comedy when she was 11.

The following year young Blaise wrote an article on solid geometry which
drew the attention of Rene Descartes (the main French mathematician at the
time). Descartes couldn't believe such an article could have been written
from anyone so young. The two developed a special relationship.

In 1642, when he was 19, he started work on a calculating machine to help
his dad count those taxes - the first ever digital calculator, called a
Pascalaline, akin to the ones that were popular in the 1940s.

Blaise Pascal's life as a mathematician went on to produce the Pascal's
triangle which is a triangle of numbers starting with 1 and then extending
down left and right with each number equalling the sum of the numbers above
left and right. It gives the values of the polynomial coefficients, useful
in algebra and differential calculus.


Philosophical Disagreements
Blaise was intrigued with these vacuums and spent a few years reproducing
Torricelli's experiments and trying out different liquids such as water
versus red wine. In 1647 he wrote some papers on the properties on the void
at the top of barometer (Expériences nouvelles touchant le vide).
Then he and Rene Descartes have some long chats about this topic. Descartes
could not believe that a void or vacuum existed or that a barometer was
really measuring air pressure. He supported the explanation by Greek
philosopher Aristotle that this space was filled with a substance called
aether, which was extremely tenuous and able to flow through tiny pores in
the glass tube and fill in the space left by the receding water. The aether
was also used by Aristotelians to explain how light from far-away stars
reaches us by travelling through a substance. Things came to a pretty pass.

Scientific experimental evidence
Blaise understood the power of experimental evidence and so he then built a
portable barometer using a glass tube of mercury inverted into a dish of
mercury. Because he had weak knees, he asked Jaqueline's then husband Florin
Périer, to do the hard bit - carry this device up the Puy de Dôme, a
conspicuous mountain in Rouen familiar to Blaise from his childhood, and
take a series of measurements. Sure enough, the height of the supported
mercury column got less with increasing altitude. The amount of fluid in the
tube was responding to changes in air pressure. So, it was air pressure that
was responsible for the height of the column, rather than the size of any
void left over at the top. This experiment was carried out on 19 September
1648 and verified Evangelista Torricelli's original hypothesis about
atmospheric pressure on the equilibrium of liquids.

Le Puy de Dôme in central France, site of famous PASCAL experiment

The Puy de Dôme experiment became famous in the world of science for finally
putting an end to the Aristotelians aether theory, and the principle it
proved became known as Pascal's Law.

Pascal's barometers quickly became the best tool for measuring altitude,
proving accurate enough to give good measures of the depth of coal mines. It
wasn't long before barometers were also adopted by sea-captains to help show
the dropping air pressure that precedes wet windy weather. To this very day,
even though we measure temperature, wind, rainfall, and humidity as well as
pressure—it is the PRESSURE LINES that we draw on weather maps that are
accepted as capturing and showing the weather pattern.

TROPICS
The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical
Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html

HINNAMNOR is storm force near Iwo Jima. There are zones for potential
developments west of Mexico and across the central Atlantic.

WEATHER ZONES
SPCZ=South Pacific ConvL1ergence zone and STR (Sub tropical ridge).

The SPCZ stretches from PNG across Solomons to Samoa and is expected to
drift south to Fiji/Tonga late this week. Avoid.
Low L1 to south of Tahiti is expected to drift to southwest and then to
southeast.

HIGHS and LOWS
High H1 above 1034 over NZ is expected to slowly shift to Chathams by
mid-week then speed off to the east and fade.
Low L2 over Victoria tonight is expected to weaken as it moves into south
Tasman Sea by mid-week then over NZ on Friday. This one looks tame from
Tuesday.
Models are picking L3 to deepen off Queensland at end of the week and move
onto NZ next week. Avoid.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more detail for 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 64277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Bob Blog 21 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 21 August 2022

Another reason to hate a HIGH
Back in the 1990s when I wrote my MetPack notes, still available at
about.metservice.com/our-company/learning-centre/mariners-met-pack/

I included a section listing nine reasons to Hate a High.
Last week over New Zealand has been a perfect example of reason number nine
"The bigger they are the slower they move, blocking fronts that are trying
to follow them."
I mentioned that L2 and L3 2ould bother Aotearoa NZ (AoNZ) from Tuesday to
Friday last week, and indeed they did. This is because a large High grew to
well over 1040hPa east of AoNZ and south of FP.
Notice how there was a convergence zone of tropical moisture feeding the
frontal rain stalled over AoNZ , this was referred to in the popular media
as a "hosepipe" to help convey the picture.
As a result the rain accumulation was record breaking and very damaging


TROPICS
There are zones for potential developments west of Mexico and across the
central Atlantic.

WEATHER ZONES
The SPCZ stretches from PNG across Solomons to Samoa. Early in the week a
convergence zone from around Niue to Southern Cooks is associated with L1, a
low further south that is expected to go to the southwest and fade. OK to
travel from Tahiti to Tonga this week.

HIGHS and LOWS
Last week's High over 1040 has now moved off to the east.
The next High H1 is around 1024 and more mobile. It starts the week in the
Tasman sea and travels east along 30S crossing northern NZ around Wednesday
and getting south of FP by week=end.
L2 in the Tasman Sea is expected to cross North Island on Monday night and
then go off to the southeast.
L3 is expected to form off Coffs on Wednesday and then travel southeast
crossing NZ on Friday, followed by a southerly flow.
H1 offers a brief opportunity of OK weather...it doesn't satisfy any of
those nine ways that make nasty Highs..

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more detail for 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 64277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Bob Blog 14 August

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 14 August 2022

Tides of New Zealand
Ahh.when we start moving out of the depths of winter my first reminder that
summer and brighter times are coming is the annual arrival of the new
edition of the NZ Nautical Almanac (thanks to Boat Books). It is online now
(and the astronomical data is at
www.linz.govt.nz/sea/nautical-information/astronomical-information) but
serious boats have a place on board for their own hard copy.

When the almanac arrives, it reminds me also of the time back in the early
1970s when I was doing a course in oceanography as part of my meteorological
degree at Victoria University in Wellington and we were given as homework
the task of studying the tidal movement in Wellington harbour as an example
of the application of Coriolis forcing (things that move around the southern
hemisphere feel a tug to the left).

What impressed me at the time was that the "tug to the left" from Coriolis
should cause the water in an oceanic basin in the Southern Hemisphere to
spin clockwise, but the tides around the NZ Coast rotate counter-clockwise.

The tide at Onehunga is around three and a half hours after that at
Westhaven. If ever a canal is built between these two harbours, it could be
a perpetual power station but would need locks for vessels.

The combined attraction of the Moon and the Sun generates ocean tides.
Calculating tides is not easy. Distance and angle of separation of the Sun
and Moon keep changing, and the shape and size of ocean basins complicate
the calculation, and these keep changing too. Each component has a cycle
with its own amplitude and period (a sine wave) and these are each
calculated then added back together. The main component in our area is M2
(the moon-twice-a-day component) due to the attraction of a 'virtual' Moon
placed on a perfectly circular orbit in the Earth's equatorial plane. It has
two high and two low tides per day (semi-diurnal wave). The K1 wave, with a
diurnal period, reflects declination variations of the Moon and Sun. In
certain areas, a hundred components have to be added together to obtain a
precise forecast.

An animation of M2 looks like (note that it repeats in 12hr and 25mins) is
at
/en.wikipedia.org/wiki/File:Global_surface_elevation_of_M2_ocean_tide.webm

There is a Tidal nodal point or amphidromic point (Greek for around running)
over the mainland near central New Zealand
The nearest bay to this point has been Oteranga Bay near Cook strait but now
that the centre of NZ has shifted since the Kaikoura earthquake in 2016, I
wonder if this too has changed?

Maupiha'a (also known as Mopelia) and Maupiti in the Society Islands west of
Borabora in western French Polynesia, are very close to a Tidal null point
or amphidromic point.

Although the lunar component of their tide is almost nil, there is still a
solar component, so slack water is around noon each day. There are also
ever-changing weather components. Whenever the lagoon water drains out to
sea it does so in a rush. These are NARROW PASSAGES and If a STRONG CURRENT
encounters an opposing wind or swell then a vigorous short chop results.

Maupiti's lagoon passage is on the south side of the island and may be
unsafe for several days whenever there a southerly swell.

Maupiha'a has a pass on its northwestern side. The pass can have up to a 9
knot continual outflowing current with a wall of breakers across the
entrance. In 1917 the German raider Count Felix von Luckner's three masted
schooner Seeadler was wrecked in these breakers.

Here is a link to a video of SV KOLOHE exiting from the passage on NW side
of Maupiha'a on a day when the surrounding swells where 3 to 3.5 significant
metres. The current was an estimated 5kt and encountered waves up to 2m. See
drive.google.com/open?id=1a8TWsADTKPYChc9o7YYneyEVjLUcScJG


TROPICS
Cyclone Ten is off the Mexican west coast, going NW. MEARI is fading near
Korea.

WEATHER ZONES
The SPCZ stretches from PNG to New Caledonia and from Vanuatu to Samoa. A
convergence zone/Trough from Samoa to Southern Cooks is expected to travel
northeast to FP by mid-week and then go westwards and form a low over the
Niue area by weekend. Avoid.

HIGHS and LOWS
High H1 east of Northland expected to travel southeast along 35 to 40S to
around 160W and then intensify and become slow-moving. Squash zone expected
to north of H1 from mid-week.

L1 near Tasmania expected to travel southeast across the south Tasman Sea
and fade away by mid-week.

L2 is expected to form over New Caledonia on Monday and travel southeast
crossing NZ on Tuesday to Thursday followed by another low L3 on Friday

H2 is expected to standby over eastern Australia until after L3 and then
cross the Tasman Sea this weekend.

Not a good week for departing NZ

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more detail for 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 64277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Bob Blog 7 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 07 August 2022

Thanks to Phillip Duncan of Weather Watch for sharing an interesting link
about NZ Tides at tinyurl.com/NZtidalnode explaining bout why there is a
tidal node, or amphidromic point, over mainland NZ and why the tides spin
counter-clockwise around NZ (where the Coriolis effect alone would have them
go clockwise).

REVIEW OF THE LAST MONTH (July 2022)
MetService issue a tropical analysis of the South Pacific with isobars and
streamlines, it is NOT available from their home page but from their severe
weather page (which can sometimes be otherwise empty) or at
www.metservice.com/warnings/tropical-cyclone-activity
I am now saving one image a day from this page and here is an animation of
last month's weather at youtu.be/C8x77I9Hzy8
It shows a series of six big lows forming in the Tasman Sea then crossing
NZ. Aotearoa New Zealand had their wettest July on record.

Sea Surface temperature anomalies from psl.noaa.gov/map/clim/sst.shtml show
This shows a further relaxation of the cool zone that makes up La Nina. The
surrounding C shaped ring of warm water has intensified over the North
Pacific and is strong from New Guinea to southeast of Tahiti. The Antarctic
convergence zone shows clearly. There is a marine heat wave around the north
and east coast of Russia. The Tasman Sea warmer reading shave relaxed.


Average isobars for past month (
The subtropical ridges in both the northern and southern hemisphere have
intensified. Otherwise there hasn't been much change.

Pressure anomolies for past month
The main change on this month's anomaly map is the lowering of pressure over
Canada. There has been an intensification of the High between French
Polynesia and South America. The low zones in the southern hemisphere have
all shifted east. Despite all those lows seen in the daily weather maps over
NZ, the Tasman sea is only slightly below normal here.

Zooming into the NZ area
Maps show that the subtropical ridge around NZ has shifted north, and
pressures have relaxed around the equator, relaxing the trade winds. Highs
have intensified to over 1025 in Indian and East South Pacific Ocean and
isobars over the Tasman Sea /NZ area have dropped around 5hPa.

TROPICS

The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical
Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html

clip_image012

Cyclone Nine is off the Mexican west coast, going NW. There are also areas
of potential development around China Sea. Micronesia, and central Atlantic.


WEATHER ZONES

SPCZ

The SPCZ stretches from PNG across northern Vanuatu then weakens further
east, but also stretches from near Samoa to near French Polynesia. This
branch CZ is expected to travel north until mid-week and then form a low L3
to south of Tahiti and then L3 and CZ should travel to SW. Best time to
depart Tahiti is mid-week.

Trough over New Caledonia today expected to travel east onto Fiji area by
Wednesday and towards Southern Cooks by weekend.

HIGHS and LOWS

High H1 expected to stay quasi stationary somewhat south of Tahiti and east
of NZ. Squash zone expected between H1 and L3 from mid-week.

Wintry low L1 to west of South Island is expected to travel NE across
northern NZ by Tuesday and then off to the southeast.

L2 is expected to form near Norfolk Island around Wednesday and travel east
along 30S.

H2 is expected to travel east across Tasmania by Wednesday and onto NZ by
weekend followed by a trough early next week.

L2 may help foe sailing from Aus to Noumea from mid-week.

For good voyage from Opua may need to wait until after L2.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more detail for 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 64277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>