Bob Blog 17 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 17 July 2022

DAMAGING SWELLS

On BASTILLE DAY Meteo France in French Polynesia gave RED WARNINGS for heavy
swell over much of the southern parts of the group.

www.rnz.co.nz/international/pacific-news/470918/tahiti-district-battered-by-
massive-swells

This has really excited the surfers:
www.surfline.com/surf-news/incoming-tahiti-xxl/156438
www.surfline.com/surf-news/swell-alert/code-red-ii-teahupoo-goes-xxl/156514
www.surfline.com/surf-news/code-red-swell-part-ii-comes-hawaii-california/15
6714

These damaging swells went on to Cook Islands
See
www.stuff.co.nz/travel/travel-troubles/129296095/cook-islands-tourism-takes-
another-beating-after-storm-damages-several-hotels
And American Samoa issued a state of emergency
www.rnz.co.nz/international/pacific-news/471042/state-of-emergency-declared-
in-american-samoa-due-to-severe-weather-conditions

The swells had been generated on the western side of Southern Ocean storm,
and this in itself is a regular occurrence, so doesn't explain the rarity of
this event (worst damage in decades). It was all a matter of timing. The
swell arrived just as a large HIGH was travelling east along 30South. The
easterly winds on the northern side of the high were enhanced as the isobars
around the periphery of the passing high squeezed together, producing 20 to
25kt wind that helped to pile the swells

Wave map from windy.com shows the estimated waves near Tahiti of 4.6m at 16
seconds.

The longer the period of the waves the greater the energy they contain and
the mor scouring damage they an do to a beach. The longer period also means
a flatter wave, so these swells are just gentle giants so that sail boats at
sea (away from the coast or shallows) can easily navigate them (so long as
the wind is 20kt or less).

Another factor that helps waves to sweep onto a beach is the ambient
atmospheric pressure. and the "IB" or inverse barometric effect. Average
surface pressure is 1013.25hPa and every hPa below that can raise the sea
level by a cm. This effect is most noticeable in deep lows and tropical
cyclones. It wasn't much of a factor this time

The swells also arrived when a full moon was close to moon at perigee
(closest to earth) resulting in larger than normal spring tides.

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TROPICS
DARBY is now weakening to south of Honolulu and is being followed by
ESTELLE. .
There are Zones of potential development this week around the Philippines
and across the Atlantic

WEATHER ZONES
The SPCZ is active in the Coral Sea and should help breed low L2 there this
week. with peak winds and large swells around wed and Thursday local.
There is also a trough/convergence lingering with one of its arms east of
Tahiti fading in a few days while another builds over Southern Cooks.

HIGHS and LOWS
High H1 over North Island tonight travelling east along 40S this week with a
squash zone of strong winds and large swells reaching a peak 12-15S from 150
to 160W around Wed and Thursday local.
LowL1 is in south Tasman Sea tonight. Associated fronts crossing NZ on
Mon/Tues, and Low on Wed followed by strong cold southerlies on Thursday.
H2 is expected to cross Tasmania on Thursday and NZ on Sat/Sun/Mon.

OK to sail from Tahiti to Fiji this week but avoid the squash zone.
May be a good week to avoid Coral Sea/New Caledonia area.

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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 bob@metbob.com or txt 64277762212
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