Bob Blog 30 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 30 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/wDmVQCMfqxU

July shows plenty of Southwest bursts from the Southern Ocean onto New
Zealand, showing that El Nino-type weather patterns are now occurring.
Sometimes lows lingered over northern NZ due to blocking Highs south of
Tahiti. This was a continuation of the dominate pattern in June. Here is an
example of the July pattern (9 July)

Sea Surface temperature anomalies from psl.noaa.gov/map/clim/sst.shtml
Sea temperature anomalies are warmer in the northern Hemisphere than last
month. in fact the northern Hemisphere air temperature in July 2023 broke
many heat records. Not much change with the equatorial warm patch in the
eastern Pacific the cause of the El Nino) or in the warm spots in the
Southern Hemisphere.

Average isobars for past month (below)

From www.psl.noaa.gov/map/images/fnl/slp_30b.fnl.html
Subtropical ridges have intensified. This is typical of July. The Asian
monsoon is travelling east as per normal.

Pressure anomalies for past month (below)
Higher than normal pressure reveals a heat dome over Europe and Asia. NZ
remains a breeding ground for lows and south of Tahiti still has a lingering
high. Australia and South Africa has flipped from low to high.

Zooming into the NZ area
South-westerly isobars now cover NZ. The westerly winds have relaxed at 50
to 60S

TROPICS
Cyclone DOKSURI travelled from northern Philippines to southern Taiwan and
is now being followed by KHANUN. There are tropical depressions west of
Mexico and east of the Caribbean.
The MJO, a burst of extra energy in the tropics, is moving across Indonesia.


WEATHER ZONES
The South Pacific Convergence zone is expected to build over the Coral Sea
and Vanuatu towards Samoa. An intense convergence zone/ trough is expected
to linger from Niue area to Southern Cooks. Squally Low L3 might form north
of Fiji late in the week and move SE across Tonga followed by a burst of
over 3m long -period southerly swell.
Tahiti to Tonga? Avoid L3. Looks Ok to go to Suwarrow.

HIGHS and LOWS
Low L1 well east of NZ should continue to move off to the southeast.
Low L2 is this week's main protagonist crossing the south Tasman by
Wednesday and then going NE off the NZ east coast followed by strong cold
southerly winds and over 4m swells reaching to 30S by weekend.
High H1 stays in the mid north Tasman Sea and is expected to bring OK
weather to North Island until end of Tuesday for fast boats exiting north or
going west across northern Tasman.

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