Bob Blog 7 Aug

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 07 August 2022

Thanks to Phillip Duncan of Weather Watch for sharing an interesting link
about NZ Tides at tinyurl.com/NZtidalnode explaining bout why there is a
tidal node, or amphidromic point, over mainland NZ and why the tides spin
counter-clockwise around NZ (where the Coriolis effect alone would have them
go clockwise).

REVIEW OF THE LAST MONTH (July 2022)
MetService issue a tropical analysis of the South Pacific with isobars and
streamlines, it is NOT available from their home page but from their severe
weather page (which can sometimes be otherwise empty) or at
www.metservice.com/warnings/tropical-cyclone-activity
I am now saving one image a day from this page and here is an animation of
last month's weather at youtu.be/C8x77I9Hzy8
It shows a series of six big lows forming in the Tasman Sea then crossing
NZ. Aotearoa New Zealand had their wettest July on record.

Sea Surface temperature anomalies from psl.noaa.gov/map/clim/sst.shtml show
This shows a further relaxation of the cool zone that makes up La Nina. The
surrounding C shaped ring of warm water has intensified over the North
Pacific and is strong from New Guinea to southeast of Tahiti. The Antarctic
convergence zone shows clearly. There is a marine heat wave around the north
and east coast of Russia. The Tasman Sea warmer reading shave relaxed.


Average isobars for past month (
The subtropical ridges in both the northern and southern hemisphere have
intensified. Otherwise there hasn't been much change.

Pressure anomolies for past month
The main change on this month's anomaly map is the lowering of pressure over
Canada. There has been an intensification of the High between French
Polynesia and South America. The low zones in the southern hemisphere have
all shifted east. Despite all those lows seen in the daily weather maps over
NZ, the Tasman sea is only slightly below normal here.

Zooming into the NZ area
Maps show that the subtropical ridge around NZ has shifted north, and
pressures have relaxed around the equator, relaxing the trade winds. Highs
have intensified to over 1025 in Indian and East South Pacific Ocean and
isobars over the Tasman Sea /NZ area have dropped around 5hPa.

TROPICS

The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical
Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html

clip_image012

Cyclone Nine is off the Mexican west coast, going NW. There are also areas
of potential development around China Sea. Micronesia, and central Atlantic.


WEATHER ZONES

SPCZ

The SPCZ stretches from PNG across northern Vanuatu then weakens further
east, but also stretches from near Samoa to near French Polynesia. This
branch CZ is expected to travel north until mid-week and then form a low L3
to south of Tahiti and then L3 and CZ should travel to SW. Best time to
depart Tahiti is mid-week.

Trough over New Caledonia today expected to travel east onto Fiji area by
Wednesday and towards Southern Cooks by weekend.

HIGHS and LOWS

High H1 expected to stay quasi stationary somewhat south of Tahiti and east
of NZ. Squash zone expected between H1 and L3 from mid-week.

Wintry low L1 to west of South Island is expected to travel NE across
northern NZ by Tuesday and then off to the southeast.

L2 is expected to form near Norfolk Island around Wednesday and travel east
along 30S.

H2 is expected to travel east across Tasmania by Wednesday and onto NZ by
weekend followed by a trough early next week.

L2 may help foe sailing from Aus to Noumea from mid-week.

For good voyage from Opua may need to wait until after L2.

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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 at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt 64277762212
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