Bob Blog 30 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 30 July 2023

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/wDmVQCMfqxU

July shows plenty of Southwest bursts from the Southern Ocean onto New
Zealand, showing that El Nino-type weather patterns are now occurring.
Sometimes lows lingered over northern NZ due to blocking Highs south of
Tahiti. This was a continuation of the dominate pattern in June. Here is an
example of the July pattern (9 July)

Sea Surface temperature anomalies from psl.noaa.gov/map/clim/sst.shtml
Sea temperature anomalies are warmer in the northern Hemisphere than last
month. in fact the northern Hemisphere air temperature in July 2023 broke
many heat records. Not much change with the equatorial warm patch in the
eastern Pacific the cause of the El Nino) or in the warm spots in the
Southern Hemisphere.

Average isobars for past month (below)

From www.psl.noaa.gov/map/images/fnl/slp_30b.fnl.html
Subtropical ridges have intensified. This is typical of July. The Asian
monsoon is travelling east as per normal.

Pressure anomalies for past month (below)
Higher than normal pressure reveals a heat dome over Europe and Asia. NZ
remains a breeding ground for lows and south of Tahiti still has a lingering
high. Australia and South Africa has flipped from low to high.

Zooming into the NZ area
South-westerly isobars now cover NZ. The westerly winds have relaxed at 50
to 60S

TROPICS
Cyclone DOKSURI travelled from northern Philippines to southern Taiwan and
is now being followed by KHANUN. There are tropical depressions west of
Mexico and east of the Caribbean.
The MJO, a burst of extra energy in the tropics, is moving across Indonesia.


WEATHER ZONES
The South Pacific Convergence zone is expected to build over the Coral Sea
and Vanuatu towards Samoa. An intense convergence zone/ trough is expected
to linger from Niue area to Southern Cooks. Squally Low L3 might form north
of Fiji late in the week and move SE across Tonga followed by a burst of
over 3m long -period southerly swell.
Tahiti to Tonga? Avoid L3. Looks Ok to go to Suwarrow.

HIGHS and LOWS
Low L1 well east of NZ should continue to move off to the southeast.
Low L2 is this week's main protagonist crossing the south Tasman by
Wednesday and then going NE off the NZ east coast followed by strong cold
southerly winds and over 4m swells reaching to 30S by weekend.
High H1 stays in the mid north Tasman Sea and is expected to bring OK
weather to North Island until end of Tuesday for fast boats exiting north or
going west across northern Tasman.

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

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 23 July 2023

Waves: Height(m) x Height (m) x period (Sec) = Power (in KW/m)
This is a simple approximation for estimating wave power.
So a 2m wave with period 7 sec has power of 28 kW/m
And a 4m wave with a period 7sec has Power 112 kW/m (four times more)
This is based on some lecture notes in a training video at
www.youtube.com/watch?v=2ODs5lxqRdw


TROPICS
TALIM uprooted trees in South China, remnants of CALVIN skirted around
southern Hawaiian Islands, DON went across the north Atlantic and DOKSURI
spun up east of Philippines.
The MJO, a burst of extra energy in the tropics, is on the move and expected
to visit the Indonesian longitudes in the next week or so and reach west
Pacific early August.

WEATHER ZONES
The South Pacific Convergence zone is expected to extend from Coral Sea to
Vanuatu and Samoa.
Low L1 near Niue is moving off to the southeast and associated convergence
zone is expected to travel east and cross southern cooks late this week.
HIGH H1 well east of NZ and at 45S is quasi -stationary and drifting east,
blocking the lows on its western shoulder.
Low L2 near Chatham Islands tonight is being steered southwards around H1,
maintaining a cold snap and a southerly flow over New Zealand.
In this southerly flow a second cold burst crosses NZ on Wed and then turns
into low L3 off North Island that curves to the SE. This is followed by a
third cold burst and then low over northern NZ next weekend.
After that HIGH H2 might finally have a chance to cross the northern Tasman
Sea early next week.
The southerly flow over NZ this week is likely to reach as far as Minerva,
and the swells may be over 3m at times.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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).
Text archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt 64 277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Bob Blog 16 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 16 July 2023

The incoming El Nino and New Zealand weather by Dr Kevin Trenberth
See this link
theconversation.com/el-nino-combined-with-global-warming-means-big-changes-f
or-new-zealands-weather-207493


TROPICS
Things are getting busy in the tropics as is typical in July, with DON in
the North Atlantic, CALVIN in the North Pacific and TALIM in the China Sea.
The MJO, a burst of extra energy in the tropics, is on the move and expected
to visit the Western pacific in a few weeks.

WEATHER ZONES
The Tropics
The South Pacific Convergence zone is expected to extend from Coral Sea to
Fiji and to combine with a jetstream aloft stretching its clouds to southern
Tonga.
A convergence zone/Front now over the Southern Cooks is expected to travel
north onto Tahiti by local Wednesday and Tuamotu Islands around local
Thursday followed by a change to moderate southerly winds.
An active LOW L3 and trough is expected to form over Fiji by local Thursday
and then go SE and reach Rarotonga on local Friday preceded by strong NE
winds, accompanied by rain, and followed by westerly winds. Avoid.
If travelling from Tahiti to Tonga this week, then consider talking the
northern route via Suwarrow.

HIGHS and LOWS
Low L1 near Chatham Islands tonight is travelling steadily off to the ENE
and is expected to deepen to around 990 followed by a burst of southerly
swell extending as far as 14S.
HIGH H1 in central Tasman Sea should travel east along 30S crossing
Northland on local Tuesday.
Low L2 is expected to come from the Southern Ocean and cross NZ on Wednesday
and Thursday deepening to below 1000 around Northland on Friday. It is
followed by a bust of SW wind and swell getting as far as 15S by the
weekend. 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).
Text archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt 64 277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Bob blog 9 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 9 July 2023

Weather regimes - SAM

Us humans love finding patterns in things. Our orbit around the sun is so
repeatable and predictable that we have "seasons". Watching weather maps
long enough, one can see that sometimes the same weather system may repeat
in clusters. We like to seek signs that predict changes.

Tonight, I'll blog about SAM, the southern annular mode. This is a measure
of the average speed of the westerly winds around the Polar vortex (the ring
of westerly winds that circle the planet between 50S and the Antarctic
circle (66 S). The value of SAM alters the north-south movement of this
vortex. A high positive value of SAM occurs when the air pressure over
Antarctica is lower than normal, and westerly winds in the polar vortex are
stronger than normal (note, the actual isobars over Antarctica are always
higher than those in the polar vortex, but SAM works with the anomaly
values, not the actual values). So, in a high positive SAM the polar vortex
is shifted southwards, and pressures is the mid-latitudes are higher than
normal, with weaker winds and settled weather.
Read more in blog.metservice.com/Southern-Annular-Mode

However, when SAM is negative, the polar vortex is weaker, and may spread
outwards, so that west to southwest winds over the mid-latitudes are
stronger than normal--- the chances are that there may be a POLAR BLAST.
Negative SAM phases can lead to a displacement of the westerly winds and
allow cold air outbreaks to extend further northward into the mid-latitudes.
Therefore, monitoring SAM can provide valuable information for forecasting
polar outbreaks.

SAM refers to surface winds 50S-66S. A proxy of SAM is available, namely the
AAO or Antarctic Annular mode (average 700hPa Z wind component 20S to 90S)
at
www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/new.aao_inde
x_ensm.html
This jumped negative on 28 June and a polar blast brought much-wanted snow
to NZ ski fields. SAM has since stayed negative and there have been decent
snowfalls over SE Australia the last few days. Another minor polar blast is
expected to reach NZ around Wednesday as seen here on windy.com.

TROPICS
Cyclone BEATRIZ dissipated after skirting the Mexican coast near the port of
Manzanillo.
There are areas of potential development eat of Philippines and west of
Mexico, and two point of interest being closely watched, but no cyclones
tonight.
The MJO, a burst of extra energy in the tropics, remains weak and near the
Indian Ocean.

WEATHER ZONES
The South Pacific Convergence zone is expected to slowly rebuild over the
north Coral Sea ran extend eastwards to Samoa. A trough is expected to move
east across Tonga around 14 or 15 July and then further east the next few
days. If sailing from Tahiti to Tonga then maybe find safe harbour by time
the trough arrives. The southerly swells that reached as far as 17S last
week should be mostly gone this week.

HIGHS and LOWS
Low L1 is 980 off east of North Island and moving slowly southeast. Tues and
Wed may be the only OK days to depart NZ for tropics this week.
Low L2 is expected to travel across South Tasman Sea at 50S and on Wednesday
to go northeast towards Chatham Islands, followed by a cold southerly flow
over NZ. There
High H1 over central Australia is expected to slowly move into central
Tasman Sea after mid-week. There is expected to be a SQUASH ZONE of enhanced
SE trade winds on its northern side that may spread as far as Southern Cooks
by 20 July. 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
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Bob Blog 2 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 2 July 2023

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/x_RC3Wn13SM
June was a transition month as El Nino weather patterns slowly kicked in.
For the first three weeks the main pattern was with a blocking High east of
NZ and lows to the north of NZ with a strong NE flow in-between. The
highlight of the month was 23rd (shortest day) with a deluge that damaged
Hawkes Bay roads.

Ten days later and the Highs are further north, and the lows are to the
south, a typical El Nino pattern.

Sea temperature anomolies are much the same as last month. The main change
has been a warming of the sea between Philippines and Japan, and an
intensification of the marine heat wave west of the Sahara.

Subtropical ridges have weakened (except in the north Pacific). Pressures
have fallen over central Asia.
The anomaly pattern in the southern hemisphere is almost the reverse of last
month's. In particular, the Antarctic have flipped from negative to
positive.

Zooming into the NZ area
The subtropical ridge has now drifted further north than last month and
weakened.
The westerly flow in the 40s and 50s is increasing, the 980 isobar has
travelled northwards almost to 50S.


TROPICS
Cyclone s ADRIAN and BRET formed off the west coast of Mexico. Adrian is
still tracking westerly and there is a high potential of another system
developing there this week.
The MJO, a burst of extra energy in the tropics, remains weak and near the
Indian Ocean.
WEATHER ZONES
South Pacific Convergence Zone SPCZ
is expected to retreat to north of 10S in the Coral Sea. With the
subtropical ridge so far north this week the forecast is for a quiet pattern
not much rain and gentle winds. With a weak trough passing over the
Southern Cooks early this week that may bring weak southerly winds over
Niue/ South Tonga, and then OK eastly weeks for the remainder of the week.
A good week for getting from Tahiti to Tonga.
However: 3m Southerly swells as far as 20S, and these may creep to 10S
Thursday to Saturday as SE swells.

HIGHS and LOWS
Low L1 is deepening off east of NZ and expected to go rapidly off to the SE
followed by a cold (snowy) southerly burst. Low L2 follows L1 bringing
another southerly burst to Chathams by Thursday.
HIGH H1 is expected to travel across Tasman and northern NZ from Tue to
Thursday. This is the first High on this path for a few weeks and offers a
brief reasonable opportunity for sailing from NZ to the tropics.
However Low L3 is expected to reach central Tasman by Friday preceded by a
northerly flow, and then to deepen over northern NZ this weekend, followed
by strong southwest winds. 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
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>