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 15 September 2024
The climate influencers
A quick review of the trends in the parameters we use to watch the main seasonal weather influencers. Thanks to bom.gov.au/climate
The Pacific
From the Pacific Ocean comes the ENSO (El Nino Southern Oscillation) parameters. La Lina is the name given to the period when sea surface temperature SST over the eastern equatorial Pacific is below normal.
In the atmosphere we monitor ENSO = El Nino/Southern Oscillation and its impact on the weather map by using. the Southern Oscillation Index SOI (30 day running mean). This is based on the standardized difference in the barometer readings between Tahiti and Darwin, in other words it counts the average number of isobars between them on the weather map. When the index stays above 7 (on the scale shown here) for more than a month we call it an LA NINA event.
This is showing that after neutral territory during winter , The SOI is no indicating a swing towards La Nina.
The Ocean:
The parameter used from the ocean is based on the sea surface temperatures in the equatorial eastern Pacific and called the NINO 3.4 SST anomaly.
International research Institute IRI have compiled the predictions for all the models as shown here from iri.columbia.edu. The consensus is that according to the Dynamic models there may be a weak LA NINA from October to February.
Expected impact in the South Pacific
The cooler than normal lounge of surface water across the east equatorial Pacific tends to nudge the South Pacific Convergence zone southwards. This makes the trade winds stronger than normal and shifts the subtropical ridge southwards. In spring this concentrates the disturbed westerly winds of the roaring forties. In summer the path taken by migratory Highs from south of Australia is across the Tasman Sea and along 40S, encouraging a northeast flow onto northern NZ. The peak cyclone prone area hugs Vanuatu.
However, each La Nina event is different and even a strong event only explains around 20% of the observed weather variance.
Tropics
The MJO Maden Julian Oscillation is the name given to a measurable increase in intensity that travels eastwards around the planet around once a month mainly along the Intertropical convergence Zone and affects tropical weather.
A good diagram of its current intensity and expected future for the next few weeks is at
www.cpc.ncep.noaa.gov/ --- in these maps BLUE is extra cloudiness associated with MJO and yellow is extra sunshine.
It is likely that with the MJO recently over Indonesia, it may have been associated with formation of Cyclone YAGI. MJO is expected to move east into the pacific Ocean over next few weeks and fade way.
Southern Ocean
For the Southern Ocean comes the SAM parameter (Southern Annular Mode). This measures the strength of the polar vortex, a ring of westerly winds circulating around Antarctica between 50 to 60S. When positive, polar outbreaks are few, and when SAM is negative polar outbreaks are encouraged.
After a long negative period, a few months ago, SAM is now positive, but is expected to drop over the next weeks. This is consistent with the snowy southerlies expected over SE Australia and South Island this week.
Rounding up the Climate Dogs
Agriculture Victoria have compiled some animated cartoons explaining six seasonal weather parameters as dogs with different characteristics see
agriculture.vic.gov.au/climate-and-weather/understanding-weather-climate-and-forecasting/the-climatedogs-the-six-drivers-that-influence-victorias-climate
and watch six climate docs: Ridgy, Eastie, ENSO, Indy, Sam and MoJo strut their stuff.
TROPICS
Around 200 people were killed in flash floods and mudslides triggered by Typhoon Yagi, which swept from South China's Hainan Island to northern Vietnam. Yagi was the most powerful storm the region had seen in decades. * Tropical Storm Bebinca is forecast to become a powerful typhoon before striking the Chinese coast near Shanghai this week. * Louisiana and parts of coastal Texas were battered by Hurricane Francine, which later caused flooding across the lower Mississippi Valley
WEATHER ZONES
The South Pacific Convergence zone is sitting over Solomon Islands and extends to Rotuma and Samoa and then to the southeast across Southern Cooks. A passing trough tonight west of Fiji is expected to travel east across Tonga and Niue early in the week and reach Southern Cook and Tahiti late in the week. This trough is expected to be accompanied by a lull and some squalls and followed by a day or two of SW swells.
HIGHS and LOWS
HIGH H1 remains slow moving well south of Tahiti.
A broad trough with many parts is crossing NZ area on Monday and Tuesday then is expected to deepen into a Low L1 near Chatham Islands. This maintains a cold strong southerly flow over NZ on Wednesday followed by a period of disturbed westerlies for the remainder of the week.
HIGH H2 is expected to travel across Australia and then from mid-week go east along 25S across northern Tasman Sea as a disturbed westerly flow spreads onto NZ
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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 text 64277762212.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
15 September 2024
08 September 2024
Bobgram 8 Sep
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 8 September 2024
The disturbed westerlies of spring
The annual climate of Hs (Significant wave height) around the planet
follows the seasons with a winter peak and summer minimum. As seen at
www.researchgate.net/figure/Climatological-distributions-of-the-averag
ed-Hs-MAS-significant-wave-height-simulated-by_fig3_370153387
However, in springtime there is the disturbed westerly pattern .
Since mid-August we have been having several examples of the weather
pattern termed "disturbed westerlies". On the weather map over
Australia /NZ and the South Pacific (south of the subtropical ridge)
we usually have a High and ridge followed by a Low and trough then
another High and so forth.
As we approach the equinox, the sun dawns again around the Antarctic
circle. Just as the coldest time of the day is around dawn, so it is
that the coldest time of the year around Antarctica is around the
equinox. This then is the time of the year when there is the strongest
temperature difference (delta T) between tropics and pole in the
southern hemisphere. And it is simple physics that the stronger the
delta T the stronger the wind speed and hence the higher the swells.
With the stronger delta T the weather pattern in the midlatitudes
turns more topsy-turvy, and instead of the High -low-High-low parade
there may be three or four troughs between the highs. This is the
pattern called "disturbed westerlies"
This year the disturbed westerlies seem to have come early as the NW
winds from Australia bump into the southerlies from the Southern
Ocean. The extra friction has been producing extra static and extra
lightning in the Tasman Sea. This is consistent with an incoming La
Nina, and if that happens then there may be an early end to these
disturbed westerlies, maybe during November.
I asked Chat GPT to write a sonnet about disturbed westerlies.
The Winds of Spring in Tasman's Rolling Tide
When westerlies, disturbed, sweep through the sea,
They bring the breath of storms to ocean's flow,
As winds twist in wild uncertainty,
And the light of spring begins to grow
From warmer lands the northern breezes fly,
While polar chills rush in to clash and churn,
These winds contend beneath the shifting sky,
When orbit of earth and season steadily turn.
Across the Tasman waters swirl and rise,
Restless westerlies their course ignite,
A dance of air and sea before our eyes,
In spring's embrace, both fury and delight.
So: sailors watch these winds with cautious eyes,
For springtime's song is sung in stormy skies.
Not bad, but I had to edit some bits, Chat GPT came up with Spring's
dimming light????
TROPICS
We are having a lull at present after a busy period. Typhoon Shanshan
left seven people dead and around 130 others injured as one of the
strongest storms to hit Japan in decades. . Downpours in the northern
Philippines triggered by Tropical Storm Yagi killed at least 14 people
in landslides, floods and swollen rivers. Tropical Storm Asna spun up
over the Arabian Sea.
WEATHER ZONES
The South Pacific Convergence zone is sitting over Solomon Islands and
extends to Samoa and then to the southeast across Southern Cooks. This
zone has been producing small squally lows that bring over40kt for
between a few hours and a few days. Avoid.
HIGHS and LOWS
HIGH H1 is moving steadily east along 30 to 35S off to east of NZ.
Low L1 belongs to a trough that is crossing NZ on Monday then moving
off to the east followed by H2 on Wednesday
Low L2 is expected to belong to a trough that crosses NZ on Friday,
followed by a "disturbed westerly flow" which blurs the details of
next 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 text 64277762212.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Disclaimer: Weather is a mix of pattern and chaos; these ideas are
from the patterned world.
Compiled Sunday 8 September 2024
The disturbed westerlies of spring
The annual climate of Hs (Significant wave height) around the planet
follows the seasons with a winter peak and summer minimum. As seen at
www.researchgate.net/figure/Climatological-distributions-of-the-averag
ed-Hs-MAS-significant-wave-height-simulated-by_fig3_370153387
However, in springtime there is the disturbed westerly pattern .
Since mid-August we have been having several examples of the weather
pattern termed "disturbed westerlies". On the weather map over
Australia /NZ and the South Pacific (south of the subtropical ridge)
we usually have a High and ridge followed by a Low and trough then
another High and so forth.
As we approach the equinox, the sun dawns again around the Antarctic
circle. Just as the coldest time of the day is around dawn, so it is
that the coldest time of the year around Antarctica is around the
equinox. This then is the time of the year when there is the strongest
temperature difference (delta T) between tropics and pole in the
southern hemisphere. And it is simple physics that the stronger the
delta T the stronger the wind speed and hence the higher the swells.
With the stronger delta T the weather pattern in the midlatitudes
turns more topsy-turvy, and instead of the High -low-High-low parade
there may be three or four troughs between the highs. This is the
pattern called "disturbed westerlies"
This year the disturbed westerlies seem to have come early as the NW
winds from Australia bump into the southerlies from the Southern
Ocean. The extra friction has been producing extra static and extra
lightning in the Tasman Sea. This is consistent with an incoming La
Nina, and if that happens then there may be an early end to these
disturbed westerlies, maybe during November.
I asked Chat GPT to write a sonnet about disturbed westerlies.
The Winds of Spring in Tasman's Rolling Tide
When westerlies, disturbed, sweep through the sea,
They bring the breath of storms to ocean's flow,
As winds twist in wild uncertainty,
And the light of spring begins to grow
From warmer lands the northern breezes fly,
While polar chills rush in to clash and churn,
These winds contend beneath the shifting sky,
When orbit of earth and season steadily turn.
Across the Tasman waters swirl and rise,
Restless westerlies their course ignite,
A dance of air and sea before our eyes,
In spring's embrace, both fury and delight.
So: sailors watch these winds with cautious eyes,
For springtime's song is sung in stormy skies.
Not bad, but I had to edit some bits, Chat GPT came up with Spring's
dimming light????
TROPICS
We are having a lull at present after a busy period. Typhoon Shanshan
left seven people dead and around 130 others injured as one of the
strongest storms to hit Japan in decades. . Downpours in the northern
Philippines triggered by Tropical Storm Yagi killed at least 14 people
in landslides, floods and swollen rivers. Tropical Storm Asna spun up
over the Arabian Sea.
WEATHER ZONES
The South Pacific Convergence zone is sitting over Solomon Islands and
extends to Samoa and then to the southeast across Southern Cooks. This
zone has been producing small squally lows that bring over40kt for
between a few hours and a few days. Avoid.
HIGHS and LOWS
HIGH H1 is moving steadily east along 30 to 35S off to east of NZ.
Low L1 belongs to a trough that is crossing NZ on Monday then moving
off to the east followed by H2 on Wednesday
Low L2 is expected to belong to a trough that crosses NZ on Friday,
followed by a "disturbed westerly flow" which blurs the details of
next 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 text 64277762212.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
01 September 2024
Bobgram 1 Sep 2024
Bob Blog 1 Sep
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 1 September 2024
A review of last month's weather
Here is a link to a YouTube clip giving an animated loop of the
isobars and streamlines in the South Pacific for the last month at
youtu.be/h0FhIw4kZzs
The main pattern for August was a migratory HIGH travelling east along
around 25 to 35S followed by a trough or two, sometime three with
disturbed westerly wind south of 40S.
The tropics in the South Pacific were quiet.
The Kuroshio current has spread out into the north Pacific. The
equatorial Atlantic remains warmer than normal. The cool seas of a LA
NINA are spreading westwards from Galapagos to the dateline along the
equator.
During August the Monsoon spread east across Asia.
and the subtropical ridge in northern hemisphere weakened.
An equatorial trough developed in the mid Pacific.
The anomaly pressure pattern for August shows ridging over North
America,
Higher than expected pressures accompanying the Asian Monsoon,
and lower pressures than normal in the southern roaring 40s but for
high pressures around South America.
The roaring 40s have travelled northwards onto the South Island.
The 1015 line has shifted from near Campbell Island to near
Christchurch.
TROPICS
Powerful Typhoon Shanshan lashed Japan's southernmost islands with up
to Category-4 force before the weakened storm later caused damage and
severe flooding to Kyushu Island. . Hawaii's Big Island received flash
flooding and some wind damage from Hurricane Hone, which passed just
to the south. ASNA is near Yemen.
WEATHER ZONES
The South Pacific Convergence zone is sitting over Solomon Islands and
extends to Rotuma and Samoa and then to the southeast across Southern
Cooks. A trough and low L1 to south of Southern Cooks are moving a
windy rain band southward, followed by a lull in the trade winds.
Mostly OK this week for sailing to the west.
HIGHS and LOWS
HIGH H1 has been blocking movement south of Tahiti.
Low L2 is a secondary travelling quickly eastwards along around 45 to
50 S. Associated trough is expected to bring a cold southerly change
to NZ on Tuesday/Wednesday. It's primary Low is in the Southern Ocean.
Following that trough there is expected to be a burst of southwest
swell to over 5 significant metre sin the Tasman Sea. This should
travel north with 3+ m swells reaching Fiji on Thursday. Avoid. Low
L1.
For New Caledonia: The trough associated with L2 is expected to bring
a southerly change late Tuesday. The HIGH H2 moving along 30S into the
Tasman Sea after L2 is expected to develop a squash zone of strong SE
winds near New Caledonia and in the Coral Sea from Wednesday to
Saturday. 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 text 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 1 September 2024
A review of last month's weather
Here is a link to a YouTube clip giving an animated loop of the
isobars and streamlines in the South Pacific for the last month at
youtu.be/h0FhIw4kZzs
The main pattern for August was a migratory HIGH travelling east along
around 25 to 35S followed by a trough or two, sometime three with
disturbed westerly wind south of 40S.
The tropics in the South Pacific were quiet.
The Kuroshio current has spread out into the north Pacific. The
equatorial Atlantic remains warmer than normal. The cool seas of a LA
NINA are spreading westwards from Galapagos to the dateline along the
equator.
During August the Monsoon spread east across Asia.
and the subtropical ridge in northern hemisphere weakened.
An equatorial trough developed in the mid Pacific.
The anomaly pressure pattern for August shows ridging over North
America,
Higher than expected pressures accompanying the Asian Monsoon,
and lower pressures than normal in the southern roaring 40s but for
high pressures around South America.
The roaring 40s have travelled northwards onto the South Island.
The 1015 line has shifted from near Campbell Island to near
Christchurch.
TROPICS
Powerful Typhoon Shanshan lashed Japan's southernmost islands with up
to Category-4 force before the weakened storm later caused damage and
severe flooding to Kyushu Island. . Hawaii's Big Island received flash
flooding and some wind damage from Hurricane Hone, which passed just
to the south. ASNA is near Yemen.
WEATHER ZONES
The South Pacific Convergence zone is sitting over Solomon Islands and
extends to Rotuma and Samoa and then to the southeast across Southern
Cooks. A trough and low L1 to south of Southern Cooks are moving a
windy rain band southward, followed by a lull in the trade winds.
Mostly OK this week for sailing to the west.
HIGHS and LOWS
HIGH H1 has been blocking movement south of Tahiti.
Low L2 is a secondary travelling quickly eastwards along around 45 to
50 S. Associated trough is expected to bring a cold southerly change
to NZ on Tuesday/Wednesday. It's primary Low is in the Southern Ocean.
Following that trough there is expected to be a burst of southwest
swell to over 5 significant metre sin the Tasman Sea. This should
travel north with 3+ m swells reaching Fiji on Thursday. Avoid. Low
L1.
For New Caledonia: The trough associated with L2 is expected to bring
a southerly change late Tuesday. The HIGH H2 moving along 30S into the
Tasman Sea after L2 is expected to develop a squash zone of strong SE
winds near New Caledonia and in the Coral Sea from Wednesday to
Saturday. 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 text 64277762212.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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