Bob Blog 31 July

Bob Blog 31 July
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 31 July 2022

Nature abhors a void "Horror Vacui"

This was the level of understanding prior to Galileo who in 1632 published
his Dialogue Concerning the Two Chief World Systems
(en.wikipedia.org/wiki/Dialogue_Concerning_the_Two_Chief_World_Systems)

The following year this book was condemned by the Vatican but praised by
Evangelista Torricelli, one of his young students (then 25 years old).

Evangelista was the son of some poor textile workers, and was sent as a lad
to his uncle, a monk, for training. At age 16 his father died, and his uncle
sent him to Rome under the tutelage of Benedictine monk Benedetto Castelli.
Castelli was a student of Galileo and also entrusted by Pope Urban VII with
hydraulic experiments. This combination is what led him to the invention of
the barometer in 1643. His name lives on in the naming of the metric unit
for absolute pressure TORR.

Here is how Torricelli invented the barometer. Galileo observed that a
common suction pump could not raise water to a greater height than about 10m
(32 ft). He considered that the "abhorrence" was limited to 32 ft and
discussed this with Torricelli. After Galileo's death in 1642 Torricelli
asked what if we live in a "sea of air" that has weight and exerts pressure
like water. The suction pump lifts water up a tube - the piston closes off
access to air pressure at the top of the tube, but the air still pushes down
on the surface of the water outside the tube. This push causes the water to
rise until the weight of the lifted water equals the weight of the air push.

Now Evangelista had access to large vats of mercury in the lab basement
collected by students heating local rocks with Bunsen burners. He knew the
weight of mercury is 13 times heavier than water so that would reduce the
height of the lifted column from 10m to 76 cm. He asked a glass maker to
produce a glass tube about a quarter of an inch in diameter and 4ft. long,
and hermetically sealed one of its ends; he then filled it with mercury and,
applying his finger to the open end, inverted it in a basin containing
mercury. When he released his finger, some mercury sank into the basin, but
a column remained in the tube nearly 76cm (30inches) above the surface of
the mercury in the basin. Also, at the top of the tube was a vacuum, the
first ever humanly produced sustainable vacuum, which is now called the
Torricellian vacuum. This experiment is sometimes known as the Torricellian
experiment.


The following year he wrote up this experiment in a letter to Cardinal
Michelangelo Ricci that "We live submerged at the bottom of an ocean of air"

He died 3 years later maybe from typhoid.

A thorough write up on this experiment can be found at
galileo.imss.firenze.it/vuoto/eprota.html
(Original is in Italian but has an English translation).

Stay tuned to see how this led to the barometer and then to weather
forecasting.

TROPICS
FRANK and GEORGETTE are west of Mexico and SONGDA is near Korea.

WEATHER ZONES
The SPCZ is active in the Coral Sea to Vanuatu.
Convergence zone slow-moving near Fiji on Monday and Tuesday.
A convergence zone CZ is expected to linger between Samoa and Just south of
French Polynesia.
A passing trough is expected to form over New Caledonia on Tuesday and then
travel east forming L1 between Fiji and NZ on Wednesday. L1 then moves SE
and fades. Avoid L1. Associated trough crossing Fiji/Tonga at weekend.
OK to travel from Tahiti to Fiji this week but take a northern path to avoid
the heavier swells in the south, and maybe aim to cross that CZ near Samoa.

HIGHS and LOWS
High H1 across northern NZ on Monday expected to travel east along 35S with
a squash zone at around 25S.

L2 is deep in Australian Bight early this week and expected to travel east
along 45S reaching southern NZ by end of week. Constant moist NW winds for
NZ Alps this week, strong until mid-week.

H2 forming in Tasman Sea by mid-week is expected to cross northern NZ this
weekend.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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 24 July 2022

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 24 July 2022
HEAT WAVES
Heathrow airport near London hit 40C on Tue 19 July 2022, a new record.
The cause of this heat wave was the movement of air from over the Sahara
Desert northwards to the UK where it descended and warmed "adiabatically" or
without transferring heat via evaporation or condensation. As the air falls
it encounters higher pressure and warms by compression. We are familiar with
this effect when pumping air into a tyre, but the physics of this has only
been sorted out ~200years ago and took ~300years to sort out
This is a logical application of the "Ideal gas law" which is a combination
of Boyles law (When the temperature and amount if gas remain constant , the
absolute pressure exerted by a given mass of an ideal gas is inversely
proportional to the volume it occupies) and Charles Law (When the pressure
on a sample of a dry gas is held constant, the temperature and the volume
will be in direct proportion).
In physics a "law" is a mathematical formula that fits the observations, not
a decree. The gas molecules that occupy a space just bounce around and do
their own thing, bouncing faster when compressed, and it follows these
'laws'. Boyles law was published by Robert Boyle, an English Chemist, in
1662 and Charles law was published by Jacques Charles, a French balloonist,
in the 1780s. The ideal gas law was finally constructed thanks to Amadeo
Avogadro, an Italian Count, in 1811 and to Émile Clapeyron, a French
engineer, in 1834.
Looking at the temperature and relative Humidity measurements around
London on 19 July we can see that they are inversely related. This is a good
indicator that indeed the hotter air had arrived from the drier reaches
aloft.
This coming summer we are expected to have another La Nina, like last
summer. This usually brings tropical northeasterly winds to Aotearoa New
Zealand, and these are moist and produce rising rather than sinking air, so
an initial forecast is that we may be somewhat protected from heat waves
this coming summer (the nearest source of hot dry air is Australia and only
gets to Aotearoa New Zealand in westerly winds).
<><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><
Finally, a shout out for Gulf Harbour Radio ZMH286 who run a broadcast on
shortwave radio at 5:15pm Mon to Fri, May to Nov.
In this Patricia takes and tracks yacht positions and David relates weather
information across the South Pacific.
These broadcasts are archived at www.ghradio.co.nz/live-streaming.html
During July David has also been giving weather lessons:
Lows that form following Highs, see www.youtube.com/watch?v=7XA3ZUvdFAk
The MJO, see www.youtube.com/watch?v=dXuX5tXt1b4
Trade wind surges, see www.youtube.com/watch?v=244713K2nis (on Bastille Day)
Understanding Clouds, see www.youtube.com/watch?v=C1Z3dMgxFnY
So, these files are now available for anyone interested in these topics.
TROPICS
There are no cyclones around at present but there are zones of potential
development around Micronesia, west of Mexico and in the mid-Atlantic.
WEATHER ZONES
SPCZ=South Pacific ConvL1ergence zone
The SPCZ is active in the Coral Sea and expected to travel east cross
Vanuatu on Thursday and Fiji over the weekend.
A convergence zone CZ is expected to linger between Samoa and Just south of
French Polynesia.
OK to travel from Tahiti to Fiji this week but take a northern path to avoid
the heavier swells in the south, and maybe aim to cross that CZ near Samoa.
HIGHS and LOWS
High H1 over Chathams is expected to go NE and then travel slowly east along
30south.
L1 budded off the SPCZ in the last few days and is expected to travel across
NZ on Monday and Tuesday.
L2 is expected to deepen off Sydney on Tuesday and then go east across New
Zealand on Wed/Thurs and then off to the SE.
L3 is expected to form in the south Tasman Sea on Friday and travel
northeast to be east of the South Island by Sunday,
followed by cold southerly flow for NZ on Monday 1 August.
H2 is expected to stay over central Australia this week and on Saturday move
east along 30S into the Tasman Sea
L1, L2 and L3 make it difficult to plan trans-Tasman travel this week.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

<> Negative SEO Services <>

Hello

If you ever need Negative SEO Serrvices, we offer it here
https://www.n-seo.co











Unsubscribe:
https://mgdots.co/unsubscribe/

Bob Blog 17 July

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 17 July 2022

DAMAGING SWELLS

On BASTILLE DAY Meteo France in French Polynesia gave RED WARNINGS for heavy
swell over much of the southern parts of the group.

www.rnz.co.nz/international/pacific-news/470918/tahiti-district-battered-by-
massive-swells

This has really excited the surfers:
www.surfline.com/surf-news/incoming-tahiti-xxl/156438
www.surfline.com/surf-news/swell-alert/code-red-ii-teahupoo-goes-xxl/156514
www.surfline.com/surf-news/code-red-swell-part-ii-comes-hawaii-california/15
6714

These damaging swells went on to Cook Islands
See
www.stuff.co.nz/travel/travel-troubles/129296095/cook-islands-tourism-takes-
another-beating-after-storm-damages-several-hotels
And American Samoa issued a state of emergency
www.rnz.co.nz/international/pacific-news/471042/state-of-emergency-declared-
in-american-samoa-due-to-severe-weather-conditions

The swells had been generated on the western side of Southern Ocean storm,
and this in itself is a regular occurrence, so doesn't explain the rarity of
this event (worst damage in decades). It was all a matter of timing. The
swell arrived just as a large HIGH was travelling east along 30South. The
easterly winds on the northern side of the high were enhanced as the isobars
around the periphery of the passing high squeezed together, producing 20 to
25kt wind that helped to pile the swells

Wave map from windy.com shows the estimated waves near Tahiti of 4.6m at 16
seconds.

The longer the period of the waves the greater the energy they contain and
the mor scouring damage they an do to a beach. The longer period also means
a flatter wave, so these swells are just gentle giants so that sail boats at
sea (away from the coast or shallows) can easily navigate them (so long as
the wind is 20kt or less).

Another factor that helps waves to sweep onto a beach is the ambient
atmospheric pressure. and the "IB" or inverse barometric effect. Average
surface pressure is 1013.25hPa and every hPa below that can raise the sea
level by a cm. This effect is most noticeable in deep lows and tropical
cyclones. It wasn't much of a factor this time

The swells also arrived when a full moon was close to moon at perigee
(closest to earth) resulting in larger than normal spring tides.

>>>>>>>>
TROPICS
DARBY is now weakening to south of Honolulu and is being followed by
ESTELLE. .
There are Zones of potential development this week around the Philippines
and across the Atlantic

WEATHER ZONES
The SPCZ is active in the Coral Sea and should help breed low L2 there this
week. with peak winds and large swells around wed and Thursday local.
There is also a trough/convergence lingering with one of its arms east of
Tahiti fading in a few days while another builds over Southern Cooks.

HIGHS and LOWS
High H1 over North Island tonight travelling east along 40S this week with a
squash zone of strong winds and large swells reaching a peak 12-15S from 150
to 160W around Wed and Thursday local.
LowL1 is in south Tasman Sea tonight. Associated fronts crossing NZ on
Mon/Tues, and Low on Wed followed by strong cold southerlies on Thursday.
H2 is expected to cross Tasmania on Thursday and NZ on Sat/Sun/Mon.

OK to sail from Tahiti to Fiji this week but avoid the squash zone.
May be a good week to avoid Coral Sea/New Caledonia area.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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 10 July

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 10 July 2022
THE FORECASTING DISCLAIMER
I received an interesting email this week asking as follows:
We are planning this passage imminently but are getting conflicting
forecasts. Predict wind says 2-3 metre swell with up to 20 knots but friends
said they experienced 30 knots and 5 metre swell.
What is your analysis?
In my reply I inserted the following
Note that these waves are in "significant metres". The occasional wave,
around 4 times per hour, is 50% bigger, and wind gusts are usually 40 to50%
stronger than the average wind. Hence both the models and your friends are
correct at the same time. There is also the factor that the wind across a
sailor's face is the apparent wind rather than the real wind.
So, the wind and waves mentioned in the forecast are averages and need to be
"upsized" to reflect the peaks felt by the sailor.
On 27 December 1998, the Sydney to Hobart fleet of 115 yachts was hit by a
southwesterly storm as it entered Bass Strait. Winds gusting at times to
over 70 knots combined with heavy seas over a strong flowing East Australian
Current to exact the biggest toll ever on the race. Six lives lost, five
boats sunk and a further 66 boats retired from the race. The severe and fast
developing storm caught the fleet entering Bass Strait waters and resulted
in the biggest maritime rescue operation ever in Australian waters with 55
rescued in an operation involving some 25 aircraft, six vessels and
approximately 1,000 personnel.

One of the recommendations from the Court of Inquiry into this event was as
follows:
6) THAT WEATHER FORECASTS WHICH ARE SPECIFICALLY PROVIDED FOR YACHT RACING
FLEETS CONTAIN: -
(a) AS WELL AS THE AVERAGE WINDS EXPECTED, THE MAXIMUM GUSTS OF WIND THAT
ARE LIKELY TO OCCUR.
AND (b) AS WELL AS THE SIGNIFICANT WAVE HEIGHTS EXPECTED, THE MAXIMUM WAVE
HEIGHTS THAT ARE LIKELY TO BE ENCOUNTERED.
(See the report at
cdn.ussailing.org/wp-content/uploads/2018/01/Sydney-to-Hobart-Race-Coroners-
Report-1998.pdf)
Indeed, all marine forecasts issued by the Australian Bureau of meteorology
now carry the following disclaimer:
>>>>>>>>>>>>>>
Please be aware Wind and wave forecasts are averages.
Wind gusts can be 40 per cent stronger than the forecast, and stronger still
in squalls and thunderstorms.
Maximum waves can be twice the forecast height.
>>>>>>>>
TROPICS
BONNIE made it into the Pacific for a few days then faded and is now being
followed by TC DARBY.
There are Zones of potential development this week are around the
Philippines and Central America.

WEATHER ZONES
SPCZ=South Pacific ConvL1ergence zone and STR (Sub tropical ridge).
The SPCZ is active in the Coral Sea and should help breed lows L1 an L2 this
week.
There is also a convergence zone lingering roughly along 15S between Fiji
and southern Cooks
OK to travel from Tahiti to Fiji this week but be mindful of a burst of
southerly swell from the Southern Ocean on Bastille Day 14 July and a
possible squash zone near Niue around 19 July.
HIGHS and LOWS
High H1 east of NZ is expected to move off to the NE maintaining trade winds
be-tween Tahiti and Tonga this week.
L1 is expected to form south of New Caledonia on Monday and deepen as it
travels across NZ on Tuesday.
This is followed by L2 forming in north Tasman on Wednesday and deepening as
it travels across NZ on Friday, followed by a vigorous SW flow.
H2 is expected to stay over central Australia this week and send the tongue
of a ridge across north Tasman Sea this weekend.
L1 and L2 make it difficult to plan trans-Tasman travel this week.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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 3 July

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 03 July 2022

There has been an interesting write up of my article on SUCKERS AND PUFFERS
in the July edition of at issuu.com/downunderrally/docs/ahoy-july_22/58 and
on SHAKERS AND BREAKERS in the July edition of Tell Tales at
opuacruisingclub.co.nz/wp-content/uploads/2022/06/Web-TT-0722-.pdf

REVIEW OF THE LAST MONTH (June2022)

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) of the AHOY magazine
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 https://youtu.be/Z-5-sgVSlPc

It shows a slow-moving complex Low over Tasman/NZ until mid month and a Low
between NZ and Tonga 20-23June, so there really was only one good
opportunity for sailing from NZ to Fiji last month and it was well picked by
many sailors.

Sea Surface temperature anomalies from psl.noaa.gov/map/clim/sst.shtml
shows a 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 south of Tahiti. The Águilas current extends all
the way east to south of NZ. The NW passage is almost open, and the Med is
having a marine heatwave. Tasman Sea heat wave seems to have relaxed thanks
to the June thunderstorms but a warm patch is still off Sydney, and is the
source of the flooding there tonight.

The averaged isobar map shows that the subtropical ridge in the north
Atlantic has intensified. The subtropical ridge in the Southern Hemisphere
has weakened a little.
The anomaly map shows that the lows that were bothering Australia ln May
shifted onto the Tasman/NZ area in June, and there was a similar shift from
South Africa to Indian Ocean

Zooming into the NZ area shows that the subtropical ridge around NZ has
shifted north, and pressures have relaxed around the equator, relaxing the
trade winds.

TROPICS
Things are heating up after the northern summer solstice with two cyclones
in the Atlantic BONNIE and COLIN, and two around east Asia CHABA and AERE.
BONNIE turned in a cyclone just north of Colon in Panama and has travelled
east to west along the Costa Rica/Nicaragua border.

WEATHER ZONES
The SPCZ seems to be having a holiday this week and is replaced by separated
convergence zones. One of these is Travelling east and pulling south and
expected to clear Rarotonga on local Tuesday and another is lingering in the
Coral Sea and finally expected to reach New Caledonia on local Saturday. A
weaker zone may stretch west to east from Vanuatu to Fiji to Samoa from
mid-week.

HIGHS and LOWS
High H1 expected to move east along 35S crossing NZ on Monday and reaching
south of Tahiti by mid-week.
L1 is the low off Sydney tonight bringing flood. Its associated trough is
expected to follow Hi and cross NZ on Tuesday/Wednesday and then off to the
east.
L2 is expected to form well SE of Rarotonga next few days throwing some
swell northwards.
Low L1 is expected to form in the trough that crossed NZ on Saturday and
travel SE on western side of H1.
Low L2 is expected to form on the northwest side of a trough crossing South
Island on Monday.
By mid-week another low L3 is expected to form near Lord Howe Island as High
H3 arrives over Tasmania from Aussie Bight. H3 is expected to rotate around
L3 slowing L3 in the Tasman so that H3 may cross NZ on Thursday and L3 may
cross NZ on Friday and Sat when at its peak, followed by a cold southerly
and maybe a secondary low on Sunday/Monday.

1. Not Ok to depart NZ for the tropics in northerly flow between H1 and l2
or with L2.
2. Should be Ok to depart Aus for points east late in the week after L2.
3. If wanting to get to Aus from Noumea, maybe wait until next week.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>