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 November 2022
LIGHTNING
Last week, between 16 - 25 November, the Aotearoa / New Zealand region saw
91,349 lightning strikes (Source: MetService), with around a 1/3 of those
situated over the land. All regions of the country have experienced
significant lightning activity, however of all the regions around the
country, the Waikato Region takes 1st place with 4,255 lightning strikes
over the period, followed by Westland (3,114) and Hawke's Bay (2,970).
Dunedin had the lowest recorded number of strikes, with 42 recorded over the
9-day period.
Lightning is the most damaging weather hazard for yachts. When you
anticipate it, the standard recommendation is to put some hand-held nav
instruments in the gally oven for protection for the duration, so if the
yacht is hit and losses its electrics, not all is lost.
When we have unstable air in the chimney of a shower cloud, rising water
droplets bash into sinking ice crystals and all that rubbing together rips
off electrons that float to the top, leaving an accumulating positive charge
at cloud base. Lightning occurs when the air between two electrically
charged regions can no longer keep them apart. The average discharge is
several gigajoules.
To put this in context, between the 9 days between 16-25th November
approximately the same amount of energy was discharged into the atmosphere
(or ground) as that either generated by the New Zealand National Grid or
consumed within all industry sectors in New Zealand (Source:
https://www.mbie.govt.nz/building-and-energy/energy-and-natural-resources/en
ergy-statistics-and-modelling/energy-statistics/electricity-statistics/)
TROPICS
The latest cyclone activity report is at zoom. earth and
tropic.ssec.wisc.edu and Tropical Cyclone Potential is from
www.ssd.noaa.gov/PS/TROP/TCFP/index.html
There are no named storms at present. There is a zone of potential
development in the China Sea.
WEATHER ZONES
South Pacific Convergence zone SPCZ
The SPCZ is somewhat quiet from Solomons to north of Fiji, then has an
active convergence zone/trough over southeastern parts of French Polynesia.
HIGHS and LOWS
HIGH H1 has been south of French Polynesia for a while is this week expected
to go off to the northeast.
HIGH H2 now between Fiji and NZ is expected to travel east along 30S.
HIGH H3 should stay slow-moving in the south Tasman Sea this week, and move
onto NZ at end of the week, breaking the spell of wet weather
LOW L1 formed over Wairarapa today, cancelling the Wellington Santa parade,
and is expected to travel off to the east southeast.
LOW L2 is forming around New Caledonia area and expected to deepen as it
travels southeast
LOW L3 should travel east across the south Tasman Sea.
LOW L4 is expected to deepen off Bundaberg and travel across the north
Tasman Sea late this week.
So, things are busy this week in the South Pacific, and changeable, but NZ
looks good for arrival from 3 to 6 December.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
27 November 2022
20 November 2022
Bob blog 20 Oct
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 20 November 2022
INSTABILITY AND 1012 THE MAGIC ISOBAR
The recent rains in Australia were brought about by the influx of air aloft
from the Antarctic. This cold air last week crossed the Tasman Sea bringing
with it thundery downpours that have recently reached New Zealand. When
colder than normal air resides aloft, meteorologists describe the air as
being "unstable", meaning that any rising pocket of air may be boosted
upwards by its own buoyancy. An interesting way to "defy" gravity. These
unstable clouds are the ones that produce downpours. CAPE is a good
parameter to measure instability
All clouds contain rising moist air but only a few produce rainfall.
Basically, there are three types of clouds: flat ones, wavy ones, and bubbly
ones. The factor that determines the type of cloud and any resulting
rainfall is 'upward motion'.
Flat clouds are the result of gentle large-scale upward motion created by
air rising slantwise along a slope such as a frontal boundary. These layers
of rising air have little and slow-changing buoyancy: a condition which is
called stable air. They produce rain.
Bubbly clouds are a sign of rapid upward motions which occur on a small
scale in time and space when the atmosphere has lots of triggered buoyancy,
and is called unstable. They produce showers.
Wavy clouds are produced when strong winds blow over a range of mountains on
a stable day. Supercooled cloud droplets form in the
lower pressure pockets that ripple downstream. These clouds, called
Altocumulus lenticularis, are usually dry.
In order to be able to share our cloud watching experiences with others, we
need to learn a few cloud names. The names we use were introduced in England
by chemist Luke Howard in 1802. The two main Latin words are 'Stratus' for
flat or stable and 'Cumulus' for lumpy or unstable. Combined, they describe
a flat low layer of cloud with a bumpy base as stratocumulus.
The word 'nimbus' indicates rainfall. It's used as a prefix for flat clouds,
as in 'nimbostratus' but has the suffix 'nimbus' as in cumulonimbus.
Height above the ground is divided into thirds as follows: 'Cirrus'
describes hairy looking clouds high in the sky, with the prefix 'cirro'
attached to other clouds so high that they are made of ice crystals. The
prefix 'alto' is added for middle clouds (the same meaning of the word is
used for the alto voices in a choir). Middle clouds are composed of liquid
droplets and some of these may have a temperature below zero Celsius
(supercooled). Low clouds carry no prefix and are distinguished by being
modified by the terrain or 'feeling the ground'.
Average atmospheric pressure on Planet Earth is 1013.25hPa. The nearest
isobar to this is the 1012, and indeed this is A MAGIC ISOBAR. It's the
dividing line; at any one time the isobars higher than 1012 will always be
balanced by those lower than 1012. Robert FitzRoy selected the word 'change'
to describe the 1000 to 1012 mean sea level pressure zone on a barometer.
Usually, the 1012 isobar is the straightest on the weather map. Isobars with
lower numbers are associated with cyclones called 'cyclonic'. Isobars with
high numbers are associated with anticyclones called 'anticyclonic'.
Usually, but not always, anticyclonic isobars are associated with stable
air, and cyclonic isobars are associated with unstable air.
In New Zealand flat, wavy, and bubbly clouds often co-exist, especially near
the mountains. Even when the weather map and large-scale clouds indicate a
stable day, a fresh breeze blowing onto a range of mountains from the sea
can produce cumulus clouds and showers on the windward slopes. Stability can
change during the day, often reflected in the clouds: a day may start with a
flat deck of stratocumulus which has a lumpy underbelly, and by afternoon
the cloud deck may have changed to a flat underbelly, indicating a change to
unstable air. The clouds may then burn off and break up into cumulus clouds
with lumpy tops. These changes add to the fascination of cloud watching.
Judging stability by reading weather maps and/or watching clouds is both an
art and a science.
TROPICS
There are some lows in the China Sea and southwest of Jakarta producing
near-equatorial westerly winds across Indonesia, but no named storms
tonight.
WEATHER ZONES
The SPCZ South Pacific Convergence Zone is somewhat quiet from Solomons to
north of Fiji, then has an active convergence zone/trough over southeastern
parts of French Polynesia.
The active trough between Fiji and NZ is expected to weaken in a few days.
HIGHS and LOWS
HIGH H1 east of Aotearoa NZ is still a blocking High, staying put and
helping maintain a strong subtropical ridge westwards to Australia
LOW L1 is expected to travel across the south Tasman Sea.
Around Tuesday night/Wednesday its trough should cross NZ, avoid.
And then it should travel east.
The simple zonal pattern this week makes for simple voyage planning.
Traveling from tropics to NZ means crossing the variable subtropical ridge
--- a zone of fickle winds.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the
patterned world.
Compiled Sunday 20 November 2022
INSTABILITY AND 1012 THE MAGIC ISOBAR
The recent rains in Australia were brought about by the influx of air aloft
from the Antarctic. This cold air last week crossed the Tasman Sea bringing
with it thundery downpours that have recently reached New Zealand. When
colder than normal air resides aloft, meteorologists describe the air as
being "unstable", meaning that any rising pocket of air may be boosted
upwards by its own buoyancy. An interesting way to "defy" gravity. These
unstable clouds are the ones that produce downpours. CAPE is a good
parameter to measure instability
All clouds contain rising moist air but only a few produce rainfall.
Basically, there are three types of clouds: flat ones, wavy ones, and bubbly
ones. The factor that determines the type of cloud and any resulting
rainfall is 'upward motion'.
Flat clouds are the result of gentle large-scale upward motion created by
air rising slantwise along a slope such as a frontal boundary. These layers
of rising air have little and slow-changing buoyancy: a condition which is
called stable air. They produce rain.
Bubbly clouds are a sign of rapid upward motions which occur on a small
scale in time and space when the atmosphere has lots of triggered buoyancy,
and is called unstable. They produce showers.
Wavy clouds are produced when strong winds blow over a range of mountains on
a stable day. Supercooled cloud droplets form in the
lower pressure pockets that ripple downstream. These clouds, called
Altocumulus lenticularis, are usually dry.
In order to be able to share our cloud watching experiences with others, we
need to learn a few cloud names. The names we use were introduced in England
by chemist Luke Howard in 1802. The two main Latin words are 'Stratus' for
flat or stable and 'Cumulus' for lumpy or unstable. Combined, they describe
a flat low layer of cloud with a bumpy base as stratocumulus.
The word 'nimbus' indicates rainfall. It's used as a prefix for flat clouds,
as in 'nimbostratus' but has the suffix 'nimbus' as in cumulonimbus.
Height above the ground is divided into thirds as follows: 'Cirrus'
describes hairy looking clouds high in the sky, with the prefix 'cirro'
attached to other clouds so high that they are made of ice crystals. The
prefix 'alto' is added for middle clouds (the same meaning of the word is
used for the alto voices in a choir). Middle clouds are composed of liquid
droplets and some of these may have a temperature below zero Celsius
(supercooled). Low clouds carry no prefix and are distinguished by being
modified by the terrain or 'feeling the ground'.
Average atmospheric pressure on Planet Earth is 1013.25hPa. The nearest
isobar to this is the 1012, and indeed this is A MAGIC ISOBAR. It's the
dividing line; at any one time the isobars higher than 1012 will always be
balanced by those lower than 1012. Robert FitzRoy selected the word 'change'
to describe the 1000 to 1012 mean sea level pressure zone on a barometer.
Usually, the 1012 isobar is the straightest on the weather map. Isobars with
lower numbers are associated with cyclones called 'cyclonic'. Isobars with
high numbers are associated with anticyclones called 'anticyclonic'.
Usually, but not always, anticyclonic isobars are associated with stable
air, and cyclonic isobars are associated with unstable air.
In New Zealand flat, wavy, and bubbly clouds often co-exist, especially near
the mountains. Even when the weather map and large-scale clouds indicate a
stable day, a fresh breeze blowing onto a range of mountains from the sea
can produce cumulus clouds and showers on the windward slopes. Stability can
change during the day, often reflected in the clouds: a day may start with a
flat deck of stratocumulus which has a lumpy underbelly, and by afternoon
the cloud deck may have changed to a flat underbelly, indicating a change to
unstable air. The clouds may then burn off and break up into cumulus clouds
with lumpy tops. These changes add to the fascination of cloud watching.
Judging stability by reading weather maps and/or watching clouds is both an
art and a science.
TROPICS
There are some lows in the China Sea and southwest of Jakarta producing
near-equatorial westerly winds across Indonesia, but no named storms
tonight.
WEATHER ZONES
The SPCZ South Pacific Convergence Zone is somewhat quiet from Solomons to
north of Fiji, then has an active convergence zone/trough over southeastern
parts of French Polynesia.
The active trough between Fiji and NZ is expected to weaken in a few days.
HIGHS and LOWS
HIGH H1 east of Aotearoa NZ is still a blocking High, staying put and
helping maintain a strong subtropical ridge westwards to Australia
LOW L1 is expected to travel across the south Tasman Sea.
Around Tuesday night/Wednesday its trough should cross NZ, avoid.
And then it should travel east.
The simple zonal pattern this week makes for simple voyage planning.
Traveling from tropics to NZ means crossing the variable subtropical ridge
--- a zone of fickle winds.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
13 November 2022
Bob Blog 13 Nov
Bob Blog 13 Nov
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 November 2022
BLOCKING
The high east of Aotearoa NZ has been a blocked high with little wind in the
steering field above it.
As is normal with a blocking high, lows keep forming on outs NW shoulder
between Tonga and NZ , and this has been making it difficult to form a good
voyage from Fiji southwards recently.
TROPICS
Cyclone YAMANEKO has developed in the NW Pacific and there is the potential
for formation this week to SW of Jakarta.
WEATHER ZONES
South Pacific Convergence Zone
The SPCZ is somewhat quiet from Solomons to north of Fiji, then active from
Samoa to the Australs.
Tropical Low L1 is expected to form between Tonga and NZ on Monday and
deepen as it travels south. Its associated front is expected to cross Tonga
on Monday and Tuesday.
HIGHS and LOWS
HIGH H1 east of Aotearoa NZ has been a blocked high with little wind in the
steering field above it.
HIGH H2 between New Caledonia and NZ is expected to travel east and weaken.
There should be OK voyages on the western side of this high for travel from
New Caledonia to NZ from Tuesday, and from Fiji to NZ by mid-week.
Late in the week a combination of L2 and L3 is expected to blossom into a
large low in the Tasman Sea worth avoiding . This low should then weaken and
travel south at the end of the week.
Next front crossing Northland is expected on Wed 23 Nov.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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 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 November 2022
BLOCKING
The high east of Aotearoa NZ has been a blocked high with little wind in the
steering field above it.
As is normal with a blocking high, lows keep forming on outs NW shoulder
between Tonga and NZ , and this has been making it difficult to form a good
voyage from Fiji southwards recently.
TROPICS
Cyclone YAMANEKO has developed in the NW Pacific and there is the potential
for formation this week to SW of Jakarta.
WEATHER ZONES
South Pacific Convergence Zone
The SPCZ is somewhat quiet from Solomons to north of Fiji, then active from
Samoa to the Australs.
Tropical Low L1 is expected to form between Tonga and NZ on Monday and
deepen as it travels south. Its associated front is expected to cross Tonga
on Monday and Tuesday.
HIGHS and LOWS
HIGH H1 east of Aotearoa NZ has been a blocked high with little wind in the
steering field above it.
HIGH H2 between New Caledonia and NZ is expected to travel east and weaken.
There should be OK voyages on the western side of this high for travel from
New Caledonia to NZ from Tuesday, and from Fiji to NZ by mid-week.
Late in the week a combination of L2 and L3 is expected to blossom into a
large low in the Tasman Sea worth avoiding . This low should then weaken and
travel south at the end of the week.
Next front crossing Northland is expected on Wed 23 Nov.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
06 November 2022
Bob Blog 6 Nov
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 November 2022
REVIEW OF THE LAST MONTH (October 2022)
Sea Surface temperature anomalies from psl.noaa.gov/map/clim/sst.shtml
The warm waters between New Guinea and the north of New Zealand have
intensified. Otherwise, the main pattern remains the same as in September
with the cool waters of La Nina along the Eastern Equatorial Pacific
surrounded by zones of warmer than normal conditions in the north and south
Pacific.
Average isobars for past month (below)
The Antarctic High has weakened considerably, weakening the southern polar
vortex. The Siberian high has intensified as has the Artic low increasing
the polar westerly winds over northern Europe.
Pressure anomolies for past month (below)
There has been a notable deepening of the lows over southern Australia which
has had a very wet October. Lowers pressure over the Arctic and higher
pressures over Asia and the Aleutians show there are strong westerly winds
over northern Europe.
Zooming into the NZ area
The 1015 Isobar has shifted southwards from Fiji to south of New Caledonia
and the subtropical ridge has moved off central Australia, indicating an
early trend to summer conditions.
TROPICS
Finally, a quiet week. There is a tropical depression in the south Indian
ocean well southwest of Jakarta, and another in the North Atlantic between
the Bahamas and Bermuda, but no named storms.
WEATHER ZONES
The SPCZ is increasing in activity and active from new Guinea to Vanuatu/New
Caledonia, with another convergence zone in an arc from Samoa to French
Polynesia.
Tropical Low L1 over Society Islands is traveling off to the southeast,
leaving behind a convergence zone that is expected to weaken and travel
north.
HIGHS and LOWS
HIGH H1 east of Aotearoa NZ is expected to travel steadily ENE, allowing Low
L# in the Southern Ocean to be drawn to the NE in the wake of H1.
HIGH H2 is expected to stall in the South Tasman Sea until mid-week as a
trough on the front end of L3 then travels northeast out of the Southern
Ocean bringing a southerly change to South Island. in north Tasman Sea is
expected to travel east along 30S and weaken.
This movement of H2 blocks L2 from travelling southeast so it is expected to
go south taking wind and swell with it.
This opens an avenue of light wind between Fiji and New Zealand, but within
this is a zone of squally NE winds and frontal zone associated with L2 .
AVOID.
This zone is expected to extend as far north as Minerva and reach there on
Thursday night (local). It should affect norther NZ on Friday and Friday
night and, finger's crossed, clear in time for the World Cup Rugby on
Saturday night.
AVOID arriving in NZ on Friday/Saturday 11/12 Nov and 18 to 21 Nov.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the
patterned world.
Compiled Sunday 06 November 2022
REVIEW OF THE LAST MONTH (October 2022)
Sea Surface temperature anomalies from psl.noaa.gov/map/clim/sst.shtml
The warm waters between New Guinea and the north of New Zealand have
intensified. Otherwise, the main pattern remains the same as in September
with the cool waters of La Nina along the Eastern Equatorial Pacific
surrounded by zones of warmer than normal conditions in the north and south
Pacific.
Average isobars for past month (below)
The Antarctic High has weakened considerably, weakening the southern polar
vortex. The Siberian high has intensified as has the Artic low increasing
the polar westerly winds over northern Europe.
Pressure anomolies for past month (below)
There has been a notable deepening of the lows over southern Australia which
has had a very wet October. Lowers pressure over the Arctic and higher
pressures over Asia and the Aleutians show there are strong westerly winds
over northern Europe.
Zooming into the NZ area
The 1015 Isobar has shifted southwards from Fiji to south of New Caledonia
and the subtropical ridge has moved off central Australia, indicating an
early trend to summer conditions.
TROPICS
Finally, a quiet week. There is a tropical depression in the south Indian
ocean well southwest of Jakarta, and another in the North Atlantic between
the Bahamas and Bermuda, but no named storms.
WEATHER ZONES
The SPCZ is increasing in activity and active from new Guinea to Vanuatu/New
Caledonia, with another convergence zone in an arc from Samoa to French
Polynesia.
Tropical Low L1 over Society Islands is traveling off to the southeast,
leaving behind a convergence zone that is expected to weaken and travel
north.
HIGHS and LOWS
HIGH H1 east of Aotearoa NZ is expected to travel steadily ENE, allowing Low
L# in the Southern Ocean to be drawn to the NE in the wake of H1.
HIGH H2 is expected to stall in the South Tasman Sea until mid-week as a
trough on the front end of L3 then travels northeast out of the Southern
Ocean bringing a southerly change to South Island. in north Tasman Sea is
expected to travel east along 30S and weaken.
This movement of H2 blocks L2 from travelling southeast so it is expected to
go south taking wind and swell with it.
This opens an avenue of light wind between Fiji and New Zealand, but within
this is a zone of squally NE winds and frontal zone associated with L2 .
AVOID.
This zone is expected to extend as far north as Minerva and reach there on
Thursday night (local). It should affect norther NZ on Friday and Friday
night and, finger's crossed, clear in time for the World Cup Rugby on
Saturday night.
AVOID arriving in NZ on Friday/Saturday 11/12 Nov and 18 to 21 Nov.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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