Bobgram 28 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 28 July2024

THE CLIMATE DRIVERS
We are in ENSO neutral territory
The atmospheric SOI values are near zero

As shown in data from www.longpaddock.qld.gov.au/soi/

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.
Recent forecasts show that the Sea surface temperature anomalies in
the Nino 3.4 area may might cool a little in the next six months,
possibly enough to be associated with a brief LA NINA event in OCTOBER
and then relaxes again
And so this El Nino may soon start shifting focus more to the east.
The Indian Ocean has a climate driver called the IOD or Indian ocean
Dipole , and this is expected t to be positive but relaxing over the
next few months (as seen at bom.gov.au/climate)
The Southern Ocean has a climate driver called SAM or the Southern
Annular Mode which was recently
And in the tropics the MJO is expected to have a quiet month in August

So, in summary, the climate drivers are not giving us any useful
directions over the next few months.

The main thing in the driving seat is that Sea Surface temperatures
around the world are at an all-time high, so if a mechanism appears
that can convert this extra energy into wind and rain then we can
expect record breaking stuff, but we don't know where yet.

TROPICS
Torrents from the outer bands of Typhoon Gaemi left at least 22 people
dead in severe flooding in the Philippines, which turned Manila
streets into rivers. The storm then battered Taiwan for two days,
killing three people and sinking a freighter offshore.

Tropical Storm Prapiroon drenched parts of South China and northern
Vietnam.

WEATHER ZONES
The South Pacific Convergence zone is sitting over the northern Coral
Sea and extends a finger from Solomon Islands to Tokelau. Westerly
winds between Niue and Tahiti are expected to turn Southerly in the
next few days with southerly swells over 3m reaching a peak around
Wednesday. Avoid. After that it should be OK to sail westwards.

HIGHS and LOWS

LOW L1 south of southern cooks is moving off to southeast with
southerly sell in its wake.

Hight H1 has been crossing northern NZ past few days and is expected
to travel to the Northeast towards Pitcairn Island.

LOW L2 is expected to form in a trough crossing NZ on Monday/Tuesday
around then it should shoot off to the east

LOW L3 is expected to remain slow-moving in Tasman Sea until mid-week
then move northeast to 39S and weaken over the weekend to north of New
Zealand.

High H2 starts the week over Victoria and by mid-week is over
Tasmania, then it should travel east across the south Tasman Sea and
expand as a ridge over NZ this weekend, This H3 offers a good pattern
for people wanting to sail north from NZ>

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more details about your voyage, then check
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Bobgram 21 July 2024

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 July2024

Rapid Cyclogenesis - a Weather Bomb
A Low which central pressure of 1003hPa on July 19 near New Caledonia
intensified to around 975hpa on 20 July to NE of NZ. That's more than
24hPa in 24 hour which makes it fit the definition of a weather bomb.

This is what happens when a Jetstream gets on top of a forming low. It
vents off the rising air like a spray gun, sucking air up and out and
thereby reducing the surface pressure.

As the cloud canopy associated with the jet stream peels off it
reveals the inverted comma shape of a new low centre . called an
instant occlusion as seen in this animation of satellite imagery from
Windy. youtu.be/oSGJPECSncs

As for the week ahead at Niue:
On local Friday 26 July the winds are forecast to swing from strong NE
to strong westerly, gusting over 30kt due to a passing low (call it
L3). And on Saturday 28th SWELL from the southwest then south is
forecast to rise to 5 significant metres.

L3 is followed by large SW swells from the southern ocean as shown
here for next Monday 29 July.
AVOID.

TROPICS
Gaemi and Prapiroon are near the China sea.
A minimal and unnamed tropical cyclone brought rain to central Vietnam
without being accompanied by high wind

WEATHER ZONES
The South Pacific Convergence zone is sitting over the northern Coral
Sea and extends a finger towards northern Vanuatu and Fiji. A Low is
expected to start forming in this zone near New Caledonia on Wednesday
and deepen into a LOW L3 near Niue by end of the week, and an intense
Low this weekend over Southern Cooks. AVOID.

As for sailing from Tahiti to Tonga. Need to wait a few days for winds
and sea now near Tahiti to ease, then there is an opportunity (maybe
on local Mon, but double check) for a yacht of average speed to get to
Suwarrow before the Weekend low and its large SW swells arrive. Other
possible spots such as Aitutaki/Palmerston/Niue will be no good as
stop overs in this weekend's low. So perhaps stay put this week.

HIGHS and LOWS
High H1 now well east of NZ and south of Tahiti continues to move
slowly east. Enhanced trade winds and 3m swells on its norther side
are affecting French Polynesia this weekend.

L2 is moving from Tasman Sea across NZ on local Monday and then going
off to the southeast following Saturday's weather bomb.

This is followed by High H2 from Australia to central NZ by end of
this week. Sea conditions off northern NZ should settle after L2 by
Wednesday to finally allow a good-looking voyage northward from NZ
(maybe by late Tuesday for some).

Low L3 is expected to become noticeable near Tonga on Thursday. As
explained above: avoid.

NOTE THAT I WILL BE UNAVAILABLE ON WEDNESDAY/THURSDAY (NZ DAYS) this
week as I plan to be away on village business.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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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Bobgram 14 July 2024

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 July2024

Blocking High
That High which passed slowly over NZ last week broke a record
The highest barometric pressure measured in New Zealand is now 1046.5
hPa
This beats a 135-year-old record of 1046hPa held by Wellington since
1889.
The highest sea-level air pressure in the world was recorded in Agata,
Siberia, when the barometer reached 1083.8hPa on December 31, 1968.

The more intense an anticyclone, the more isobars there are on a
weather map. The accommodate these extra isobars some end u crunching
together, making zone of strong wind.what I call squash zones. My blog
last week mentioned the Ten Reasons to hate a High and one of these
reasons is the squash zone, which last week sat across the tropics
especially between Tonga and New Caledonia.

Of course, the higher the high, the faster the fall of pressure when
the system finally weakens or moves off. And fast falling pressure is
a factor in producing depressions. So, it isn't surprising that the
forecast for this coming week includes a cold low to northeast of the
High, 2 depressions in the Tasman Sea, and 1 forming over Vanuatu.

This 1047hPa high is also a blocking high. This means there is a lack
of the usual jet streams that help highs in this part of the world to
migrate and travel steadily eastwards.
There is a NOAA website that tracks a parameter called the blocking
index
www.cpc.ncep.noaa.gov/products/precip/CWlink/blocking/real_time_sh/rea
l_time_index_nrm.shtml
It shows this blocking high standing out like a sore thumb at the
bottom and near 180.
It also shows that this winter has been spotted with several blocking
highs at various longitudes.

TROPICS
Former Category-5 hurricane Beryl left at least 18 people dead in its
wake. There was catastrophic wind damage in the Caribbean, then
flooding and tornadoes from Texas to New England. Minimal Tropical
Storm Aletta formed for a few hours off Mexico's Pacific coast.
Short-lived Tropical Storm Chris brought rain to Mexico's central Gulf
of Mexico coast

Mexico had the highest dewpoints and dampest air on the planet last
week resulting in at least 200 crocodiles to enter urban areas in the
north Mexico state of Tamaulipas.
abcnews.go.com/International/wireStory/200-crocodiles-crawl-cities-hea
vy-rains-hit-northern-111864822

WEATHER ZONES
The South Pacific Convergence zone is sitting over the northern Coral
Sea and extends a finger towards northern Vanuatu that is set to be
taken SE by L4 on Thursday.
A few passing troughs are expected around south end of French
Polynesia associated with Low L1.

HIGHS and LOWS
High H1 is a blocking High now near 45S 170W.

On its NE side L1 has formed in the cold air and is moving to the
southeast.

On its NW shoulder the NE flow into the Tasman Sea is able to breed at
least a couple of lows, with one traveling across the north Island
embedded in a front on Monday and Tuesday.

On Thursday and Friday, a new low L4 is expected to form on a
convergence zone over Vanuatu an then travel SE and intensify to be a
big system near northern NZ on Sat/Sun 20/21 July. Avoid.

If you want to depart from Northland to the tropics, then maybe best
to wait until after L4.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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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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 07 July2024

Ten Reasons to hate a high

There is a 1036 HIGH travelling east along 45S past Tasmania.

I heard my good mate David talk about its implications on Gulf Harbour
radio ZMH286 on Friday evening. He broadcasts weather info and Pamela
handles roll calls daily at 0515UTC on 8752 (or 8779 or 8297) KHz an
stream the call at https://www.ghradio.co.nz/live-streaming.html.
David quoted from his own notes (as found on their website) and my
notes on 'Ten reasons to hate a high' Thanks Dave. This high is a
good reason to dust off those notes

When extra isobars are added to a weather map to accommodate an
intense High, this squeezes the isobars already on the map closer
together. making them crunch together in zones I call squash zones.
Hence my mnemonic "when the HIGH is over 1030, its rims are going to
get dirty"

And here, for the record are my notes on
Ten reasons to hate a high (anticyclone):

Anticyclones are usually associated with light winds and sunny skies,
but they also have some undesirable attributes,
especially when they get blocked and linger:

1. Near the centre are "dead" winds and usually an area of low clouds
causing dull days called "anticyclonic gloom", or dirty air which may
turn into fog.

2 Round the rim, winds are strong. If the central pressure is
over 1030, look for a gale somewhere on the outside of a high.

3. Highs intensify the trade winds in the tropics. It may take
about a week for a high to travel eastwards past New Zealand, and
during this time the stronger trade winds tend to give night-time rain
to the eastern side of the larger tropical Islands. In Fiji this is
sometimes called BOGI WALU.

4. The bigger the highs are, the slower they move, blocking the
fronts and lows that are trying to follow them. When this block is
released, the west-ern ("back") end of a high may become a breeding
ground for storms.

5. Intensifying highs tend to squash together the isobars between
themselves and any nearby low pressure centres, creating "squash
zones".

6. A deepening low-pressure system and an intense or lingering
anticyclone get together like the arms of an eggbeater and create a
zone of enhanced wind and rain.

7. As air flows around a high, it spins out across the isobars and
speeds up until it is as much as 20% MORE than that indicated by the
isobar spacing.

8. If a range of mountains blocks the air flowing around a high, the
air tends to squeeze around the mountains rather than flow over them.
This splits the wind flow over New Zealand into rivers of wind and
puddles of calm. Some-times a narrow gap is made just above the
mountains through which pent-up air may be suddenly released at a
rapid rate.

9. In winter and spring, a high may bring unwelcome frost.

10. In summer and autumn, a high may allow sea breezes to converge
and, if it is cold enough aloft, this can form thunderstorms and hail.


TROPICS


. Hurricane Beryl killed at least six people while pummelling
islands of the Caribbean as the earliest Category-4 and Category-5
storm on record. Beryl was fueled by unprecedented oceanic warmth
across the Atlantic basin and a lack of wind shear.
. Short-lived Tropical Storm Chris brought rain to Mexico's central
Gulf of Mexico coast.

WEATHER ZONES

The South Pacific Convergence zone is sitting over the northern Coral
Sea and extends from Solomons to northern Vanuatu to Samoa and is
getting stronger this week.
There are some passing troughs from Southern Cooks to south of French
Polynesia. A Low-pressure system is located south of Easter Island
this week.

HIGHS and LOWS
High H1 over 1036 is travelling slowly along 45S this week crossing
central NZ on Tuesday to Thursday with a squash zone of enhanced SE
winds on its northern side and some squash zones with swells over 4m.
Avoid.
Once the High moves off and isobars relax, air is expected to pile up
on itself and produce Lows at the "shoulders" of the High. A trough
is expected to form along the eastern aussie seaboard from Wednesday
so that there should be a strong NE flow moving onto NZ this weekend
or early next week followed by a trough/Low. Avoid.

If you want to depart from Northland to the tropics, then there
should be a brief window mid-week that avoids the squash zones to the
north and the incoming NE winds.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>