Bob Blog 9 Jan

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 January 2022

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 cloud 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. As the saying goes" When
barometer is over a thousand and thirty, weather can get dirty".

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
northwestern ("back") end of a high is a zone where the barometer "falls"
and may become a breeding ground for storms. The tropical low affecting Fiji
tonight is an example of this.

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 in-between where the isobars are straightest and barometer is
"steady".

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. Terrain effects: At present the windy.com wind map is showing strong
winds around East Cape and through Cook Strait.

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.
Sometimes 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 the clear night skies in 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. Today's
MetService radar is showing showers over the midriff of the northern North
Island


TROPICS
SETH finally went inland onto Queensland yesterday/Saturday, bringing severe
flash flooding (at least one death).
www.theguardian.com/australia-news/2022/jan/08/unexpected-floods-in-queensla
nd-leave-15-missing-as-ex-cyclone-seth-wreaks-havoc
The tropical depression near northwest of Fiji is currently called 03F but
may well earn a cyclone name by Monday. Check
www.met.gov.fj/aifs_prods/20036.txt

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
The SPCZ remains active from Solomons to Tuvalu to Fiji and from Samoa to
French Polynesia. Low L1 is expected to form in the southeast extension of
this zone near 30S 159W by local Tuesday and then deepen and travel to
southeast.
The tropical low T near Fiji is expected to deepen next few days and take a
slow and twisting path to the south, then, from mid-week , speed up and go
south-southeast to east of the North Island.

HIGHS and LOWS
HIGH H1 starts the week east of North Island and is expected to travel off
to the east remaining south of L1.
On Tuesday a trough in between H1 and H2 is expected to cross New Zealand,
followed by a southwest flow on Wednesday.
Then, later in the week H2 is expected to travel east across the south
Tasman Sea reaching the South Island by the end of the week.
Avoid arriving in Opua between 14 and 16 Jan due to possible strong winds
and large swells..
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If you would like more detail for your voyage, then check metbob.com to see
what I offer.
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at bottom).
Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt 64277762212
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