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.

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