Bob Blog 18 June

Bob Blog 18 June
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 18 June 23

Dr Kevin Trenberth writes to theconservation.com : Highlights

El Niño is officially here, according to the US National Oceanic and
Atmospheric Administration, and with it comes a change from the La Niña
weather patterns New Zealand has experienced for the past three years.

Moreover, it was overdue. When La Niña finally gave up the ghost in March
this year, global sea surface temperatures were suddenly the highest on
record, as the tropical Pacific abruptly began to warm.

Meanwhile, record high sea surface temperatures in the extratropical North
and South Pacific were partly a signature from La Niña and partly a sign of
global warming. The resulting "atmospheric rivers" delivered torrential
rains to California in the north and New Zealand in the south.

These sea surface temperature changes can be readily seen by comparing
variations from mean temperatures for December 2022 versus May 2023 . May
2023 shows a startling transformation throughout the central tropical
Pacific, with a coastal El Niño off Peru and Ecuador strongly evident.

Modest cooling in the eastern North Pacific is associated with the train of
storms that barrelled into the West Coast of the US and in northwest
Australia from Cyclone Ilsa.

El Niño's impacts
The weather in the tropics is seldom average, however. It tends to fluctuate
more like a roller coaster. In the atmosphere, this is referred to as the
Southern Oscillation. The combined atmosphere and ocean phenomenon is often
referred to as the El Niño-Southern Oscillation (ENSO).

The bottom of the roller coaster is the cold phase: a basin-wide cooling of
the tropical Pacific, named La Niña, while the top of the roller coaster is
El Niño, which occurs every three to seven years or so.

El Niños tend to peak in December, although their biggest atmospheric
impacts may not be until February.

The warmest years in terms of global mean surface temperature are the latter
stages of El Niño events. 2016 is the world's warmest year on record, in
part because of the very strong El Niño event. But 2023 could beat that
record – and odds are that 2024 will beat it by a lot.

Globally, El Niño is the largest cause of droughts; they are more intense,
set in quicker and increase the risk of wildfires, especially in Australia,
Indonesia and Brazil. In the weak 2019-20 El Niño, smoke from fires in
eastern Australia affected the southern hemisphere to the extent that it
blocked the sun and may have exacerbated the subsequent La Niña conditions.

Meanwhile, torrential rains are heavier, with greater risk of flooding,
especially in Peru and Ecuador. Very wet conditions can also (though not
always) occur in California and the southeast US.

New Zealand tends to experience stronger and more frequent winds from the
southwest in winter and from the west in summer during El Niño. This can
encourage dryness in eastern areas and more rain on the West Coast, with
generally cooler conditions overall.

TROPICS
Cyclone BIPARJOY moved onto India during the past week.
There is an easterly wave in the mid-Atlantic and small depression off to
the west of Mexico
The MJO, a burst of extra energy in the tropics, is weak and in the Indian
Ocean

WEATHER ZONES
South Pacific Convergence Zone
SPCZ is expected to stretch from northern Coral Sea to Samoa to Southern
Cooks. A convergence zone near 12S is likely over northern Cooks. Southerly
swells up to 3m may affect as far north as Niue to Palmerston around
mid-week.

HIGHS and LOWS
High Hi is blocked and has a squash zone of strong easterly winds on its
northern side to NE of NZ. This is generating swells and some southerly 3m
swells may make it as far as Niue to Palmerston mid-week.
H1 is knocking Low L1 over northern NZ to the SW and L3 south of the Austral
Island to the SW.
Low L2 should travel from south of Tasmania into mid-Tasman by mid-week and
then across northern NZ. Avoid. After a brief ridge Low L4 is expected to
follow L3/
Keeping this cluster of lows in the Tasman Sea this week along with H1 is
High H2 stuck over Australia.

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