Bob Blog 2 July

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 2 July 2023

A review of last month's weather

Here is a link to a YouTube clip giving an animated loop of the isobars and
streamlines in the South Pacific for the last month at youtu.be/x_RC3Wn13SM
June was a transition month as El Nino weather patterns slowly kicked in.
For the first three weeks the main pattern was with a blocking High east of
NZ and lows to the north of NZ with a strong NE flow in-between. The
highlight of the month was 23rd (shortest day) with a deluge that damaged
Hawkes Bay roads.

Ten days later and the Highs are further north, and the lows are to the
south, a typical El Nino pattern.

Sea temperature anomolies are much the same as last month. The main change
has been a warming of the sea between Philippines and Japan, and an
intensification of the marine heat wave west of the Sahara.

Subtropical ridges have weakened (except in the north Pacific). Pressures
have fallen over central Asia.
The anomaly pattern in the southern hemisphere is almost the reverse of last
month's. In particular, the Antarctic have flipped from negative to
positive.

Zooming into the NZ area
The subtropical ridge has now drifted further north than last month and
weakened.
The westerly flow in the 40s and 50s is increasing, the 980 isobar has
travelled northwards almost to 50S.


TROPICS
Cyclone s ADRIAN and BRET formed off the west coast of Mexico. Adrian is
still tracking westerly and there is a high potential of another system
developing there this week.
The MJO, a burst of extra energy in the tropics, remains weak and near the
Indian Ocean.
WEATHER ZONES
South Pacific Convergence Zone SPCZ
is expected to retreat to north of 10S in the Coral Sea. With the
subtropical ridge so far north this week the forecast is for a quiet pattern
not much rain and gentle winds. With a weak trough passing over the
Southern Cooks early this week that may bring weak southerly winds over
Niue/ South Tonga, and then OK eastly weeks for the remainder of the week.
A good week for getting from Tahiti to Tonga.
However: 3m Southerly swells as far as 20S, and these may creep to 10S
Thursday to Saturday as SE swells.

HIGHS and LOWS
Low L1 is deepening off east of NZ and expected to go rapidly off to the SE
followed by a cold (snowy) southerly burst. Low L2 follows L1 bringing
another southerly burst to Chathams by Thursday.
HIGH H1 is expected to travel across Tasman and northern NZ from Tue to
Thursday. This is the first High on this path for a few weeks and offers a
brief reasonable opportunity for sailing from NZ to the tropics.
However Low L3 is expected to reach central Tasman by Friday preceded by a
northerly flow, and then to deepen over northern NZ this weekend, followed
by strong southwest winds. Avoid.
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If you would like more details about 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 64 277762212
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