Bob Blog 21 March

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 March

The start of a new weather year
The March Equinox was 09:37UTC on 20 March and is a good point to start the
count of a new orbit around the sun (it starts the first month of the year,
Nisan in the Jewish calendar, Farvardin in the Persian Hijri calendar, or
Caitra in the Indian/Hindu calendar). The day-of-12-hours-sunlight or
equilux is a few days later in the southern hemisphere (because of
refraction of the sunbeams by the atmosphere as reported by MetService at
www.facebook.com/MetService/posts/4056722254389802

As a coincidental start to the new weather year an East Coast Low off
Australia has been giving the record-breaking conditions, with rain on the
radar from Bundaberg to Melbourne, as seen on windy.com, and with more to
come.
This system should weaken as it crosses the Tasman Sea, reaching Fiordland
on Friday.

Last Wednesday, on Saint Patrick's Day. Team NZ retained the America's Cup
in yacht racing in Auckland's Hauraki Gulf. The AIS from Marine Traffic
showed congestion as the winning yacht Te Rehutai (Ocean spirit) returned to
port.

World Met day is Tue 23 March, with theme: The Ocean, our climate and
weather, see
public.wmo.int/en/resources/world-meteorological-day/wmd-2021-the-ocean-our-
climate-and-weather

The state of the ENSO
La Nina is fading
When the Pacific trade winds are stronger than normal, they drag sun-warmed
sea surface to the west, encouraging upwelling from the cool depths around
the Galapagos. This has been going on for months giving us a "La Nina"
event. It has been shifting the subtropical ridge away from the equator.

The Ocean:
The sea surface temperatures in the equatorial eastern Pacific (area
Nino3.4) have been well into La Nina territory over the past few months and
are now relaxing and quickly returning to "normal" range.

The Atmosphere:
ENSO stands for "El Nino/Southern Oscillation". The main parameter we watch
is the Southern Oscillation Index SOI (30 day running mean) and this comes
from the weather map, summing up the whole weather pattern over the South
Pacific into one number. It counts the average number of isobars between
Tahiti and Darwin. The SOI has been more than plus one (standard deviation
from its mean) since late 2020, giving us a LA NINA event. It has now near
zero.

SOI can be seen at
www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekly
Trend in the Sea temperature anomalies, can be seen at
www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-sta
tus-fcsts-web.pdf

According to the International Research Institute of the Climate Prediction
Centre,
at iri.columbia.edu/our-expertise/climate/forecasts/enso/current/,
reviewing all of the different models for forecasting the future of this La
Nina, it has a 60% chance of transiting to normal in the next few months---
and a 40% chance of remaining much the same.

The Tropics
It is a quiet weekend with no active cyclones.

SPCZ=South Pacific Convergence zone.
SPCZ is rather broad and weak, stretching southeast from Coral Sea/Solomon
to Fiji/ Samoa then to southeast.

Subtropical ridge (STR)
BIG FAT HIGH 1036 in south Tasman Sea is expected to travel across southern
NZ around mid-week and then eastwards along 45S.
Another HIGH 1030 expected to cross Tasmania this weekend.

Aussie/Tasman/NZ troughs
Low over NW Australia expected to travel southeast and deepen rapidly off
New South wales coast by mid-week and then travel off to south-southeast
across south Tasman Sea. Avoid.

Panama to Galapagos/Marquesas
A period of variable winds in Panama mid-week, otherwise moderate northerly
winds for starters Light winds around Galapagos, turning southerly by end of
the week.
Good current to southwest then west between Panama and Galapagos. Path to
take to Marquesas this week is via NORTH of Galapagos.
There is a "mirror" ITCZ along approx. 3S from around 90W to 120W with a gap
ear 95W as seen on windy.com
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If you would like more detail for 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 atweathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt 6427 7762212
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