Bob Blog 14 Feb

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.
Issued Sunday 14 Feb

The state of the ENSO
Our summer has peaked, La Nina continues but is declining.
La Nina and El Nino are tropical drivers of our weather patterns. Their
comings and goings can last several months, maybe over a year, and so their
status can be used to help forecast the weather for the coming season.

The El Nino, with warmer than normal seas, draws the subtropical ridge
closer to the equator, weakening the trade winds, and allowing the westerly
winds of the roaring 40s to get further north. The La Nina, caused by cooler
than normal seas along the equatorial eastern pacific, shifts the
subtropical ridge away from the equator and strengthens the trade winds.

The Atmosphere:
ENSO = El Nino/Southern Oscillation. Early in the 1900s, Sir Gilbert Walker
from Britain was the Director-General of a met observatory in India, and he
searched thru world weather data looking for patterns on the weather map
across the Pacific and Indian Oceans. He found that the pressure difference
between Tahiti and Darwin helped describe the South Pacific weather pattern
in one number, and it could be used to forecast the intensity of the Indian
Monsoon (when negative, there is a drought in India). He called this
parameter the Southern Oscillation SOI. When the SOI is more than plus one
(standard deviation from its mean) for more than a month we call it a LA
NINA event, and when it stays more than minus one we call it an EL NINO
event.

The SOI has been positive since last August, reached a peak of 2 (standard
deviations above the mean) in January , and is now relaxing.

SOI can be seen at
http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekl
y

The Ocean:
Jacob Bjerknes (born in Sweden) was son of the well-known Norwegian
meteorologist Vilhelm Bjerknes (who helped develop the cyclone model as part
of the "Bergen School" in 1920s). Jacob founded the UCLA Department of Met
and in 1969 helped toward our understanding of El Nino by connecting it to
warmer than normal waters in the eastern equatorial Pacific. We now watch
SST (sea surface temperatures) in zone NINO3.4 to watch our oceanic
parameter.

This started going negative in May 2020 and reached a peak in coolness last
November and is now slowly relaxing.

According to the International Research Institute of the Climate Prediction
Centre,at iri.columbia.edu/our-expertise/climate/forecasts/enso/current/,
reviewing all the different models for forecasting the future of this La
Nina, it is expected to weaken to neutral by May 2021 (55% chance).

Impact on South Pacific
Trade winds should stretch further south than normal and may be more robust
than normal.
Tropical lows are likely to form in the Coral Sea area.

The Tropics
The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical
Cyclone Potential is from http://www.ssd.noaa.gov/PS/TROP/TCFP/index.html
TC FARAJI continues going westwards in the South Indian Ocean
There is a moderate potential for a Tropical Cyclone to form near
Micronesia, east of Philippines and around northern Australia Fiji on Monday
and move off to the south on Tuesday.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is north of its normal position and from Papua New Guinea to
Tuvalu/Tokelau
A convergence zone is expected to linger between Southern Cooks and Tahiti.
A tropical low is expected to linger around the Coral Sea and pay deepen off
Queensland coast by end of the week and then travel south.


Subtropical ridge (STR)
HIGH 1026 south of Tasmania on Monday is expected to travel across central
Tasman Sea this week and onto central NZ on Friday/Saturday.

NZ/Tasman troughs
Low 1005 to north of North Island is expected to travel south over North
island on Monday and Tuesday, with rain and strong easterly/southeasterly
winds on its southern side (southerly thru Cook Strait). Low should weaken
on Wednesday, and easterly flow should ease on Thursday.
Looks like it will be too windy for the Prada Cup on Wednesday.

Panama to Galapagos/Marquesas
Good northerly winds for starters this week. There is likely to be a good
tail current near EQ 85W, and a head current near 5-6N 85W so good idea to
go direct, or if heading for Marquesas go via south of Galapagos.
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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 mailto:bob@metbob.com or txt 6427 7762212
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