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Bob McDavitt's ideas for sailing weather around the South pacific

26 February 2023

Bob Blog 26 Feb 2023

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 26-Feb 2023

The Cyclone season.. So far

It is now almost two -thirds thru this cyclone season and time to do a quick
check on its progress. Cyclones HALE and GABRIELLE have brought lots of
damage to NZ and the impact there will take months.maybe years. to recover
from. And yet, international meteorologists may look at the statistics and
judge this season as .. UNDERPERFORMING so far.

A list of what has happened so far shows 3 named cyclones, a C1, a C2 and a
C3 and 4 tropical depressions.

The Seasonal forecast issued by NIWA back in Oct 22 went for between 6 and
10 named storms of which 3-4 may become severe and 1 may reach C5. Two
thirds of that forecast is 4-7 named storms with 2-3 being C2 or above.
Compare that to what's happened so far: 3 named cyclones and 2 that are C2
or above. So, by the numbers, so far , this season is below forecast.

TROPICS
The positive boost of the MJO cycle is crossing the South Pacific over the
next two weeks
The latest cyclone activity report is at zoom.earth and tropic.ssec.wisc.edu
and Tropical Cyclone Potential is from
www.ssd.noaa.gov/PS/TROP/TCFP/index.html

FREDDY was cat5 for a while as it approached Madagascar where it killed 7
people. It then travelled onto Mozambique and faded. ENALA is lingering in
the south Indian Ocean and expected to go south.

The potential for development across northern Australia and around Vanuatu
is above normal this week. MetService is looking at two tropical
depressions, one in the Coral Sea and the other to NW of Fiji heading for
Vanuatu
The one near Fiji has been labelled 08F by Fiji Met service and has the
following GFS ensemble forecast for its future at this stage
It is expected to peak over Vanuatu on Tuesday and Wednesday this week and
then go southeast and miss Aotearoa/NZ. Avoid.

WEATHER ZONES
South Pacific Convergence zone SPCZ

The SPCZ is expected to remain active from L3 in the Coral Sea to Vanuatu to
Fiji and Low L2 with an extension of convection southeast to L1 east of NZ.
L1-2-3 form a necklace of lows along the SPCZ.

HIGHS and LOWS
HIGH H1 over NZ is expected to travel off to the east along 50S. A trough is
expected over NZ on Friday followed by another High H2 along 45 to 50S.
These Highs should keep that necklace of lows off to the north, fingers
crossed.

Easterly winds across the north Tasman sea this week should help voyages to
the Brisbane area.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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 64 277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

19 February 2023

Bob Blog19 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.
Compiled Sunday 19-Feb 2023

GABRIELLE as I saw it
GABRIELLE proved to be historically significant. Many rivers broke their
banks bringing extensive damage to Gisborne, Wairoa, and around Napier.
Landslips were noticeable about west Auckland and Coromandel.
A snapshot of power outage for Auckland area (from VECTOR) shows over 60%
out.

As explained last week, GABREILLE did an expected right swing in its track
past Aotea /Great Barrier.
Lowest barometer reading on land was at Whitianga was 968.3 at 4am Tuesday
14 Feb (Valentine's day) when GISELLE "kissed" Coromandel.
There have been lower readings on 26 July 2008 in a winter storm.
Since Whitianga was closest to the cyclone centre it had the highest
"inverse barometer" or IB effect. Its highest total Storm surge SS occurred
around half a day before the kiss. This shows that piling up by onshore
winds can be the larger contributor, as seen in its storm surge as seen by
NIWA.
Channel island sits in the middle of Colville Channel between Aotea/Great
Barrier and Coromandel and squirts wind thru a gap. Gusts as seen on
PredictWind got to 80 knots.
Winds around Northern NZ as GABRIELLE passed by can be seen at the following
video link: https://youtu.be/FPO35_NxyS4
Thanks to MetService (and Neil Gordon) I was able to download the isobar
maps for midnight at start of 14Feb and the following noon.
As usual, where winds meet rain peaks.

Regarding the 5 days accumulated rainfall map from MetService during
GABRIELLE. The actual amounts may be much higher along the mountain ranges
(data here is based on raw data from a rain gauge network at populated
places, and not corrected for orographic effects. Also, there is some
missing data from Hawkes Bay due power cuts)
When GABRIELLE left the tropics the clouds around it assumed a "Koru"
pattern
A "koru" is the name of the pattern of an unfurling fern in New Zealand
This koru cloud sheet lingered over eastern North island as GABRIELLE slowed
down during its kiss past Aotea, hence the heavy rainfall in the onshore
winds.
Uni of Waikato has some rural gauges that measured up to 476mm in two days.

COMPARISION WITH BOLA
In March 1988 Cyclone BOLA brought significant damage to Vanuatu and New
Zealand.
Lowest measured barometer over mainland NZ during BOLA was 980 hPa.
Its track was different from GABRIELLE but both cyclones lingered offshore
northern NZ as they changed direction.
This allowed their Koru clouds to dump heavy rain onto eastern ranges for
an extended period.
I found an accumulated rain map for the Gisborne area during BOLA with a
peak of 917mm

Basically, BOLA was a three-day event and GABRIELLE may have been more
intense but was a two-day event.

TROPICS
The positive boost of the MJO cycle continues to linger around northern
Australia.
The latest cyclone activity report is at zoom.earth and tropic.ssec.wisc.edu
and Tropical Cyclone Potential is from
www.ssd.noaa.gov/PS/TROP/TCFP/index.html
Still going since last week, Cyclone FREDDY is heading for Madagascar. There
is some potential for cyclone development around northern Australia in the
coming week, but not much.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is expected to remain active across Vanuatu/Fiji/Tonga to a Low L1
that starts in the tropics and goes south-southeast. As usual the peak rain
does not correspond with the peak CAPE.
There has been active convection around western Fiji for a few days and a
flood alert has been issued.
There is expected to be some active convection around Samoa this week.

HIGHS and LOWS
After several weeks of blocking Highs east of NZ it is good to see a return
to the mobile westerly path for features in the mid latitudes. A fast moving
active front brought some squalls to Sydney on Saturday 18Feb, throwing
yachts around .. this is a sign that the pattern has changed.
So, the high H1 east of Aotearoa/NZ tonight is expected to travel east along
45S allowing a frontal trough L2 now near Tasmania to travel east across NZ
on Wednesday.
And this trough should be followed by another HIGH H2 along 45 to 50S.
The easterly winds north of H2 will hinder travel eastward from Australia
for a while.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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 64 277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

11 February 2023

Bob Blog 12 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.

Compiled Sunday 12-Feb 2023

CYCLONE GABRIELLE
The MJO cycle is spreading a positive boost of energy across northern
Australia and into the Wester Pacific this week and this has activated a
necklace of cyclones.


Cyclones DINGANI, FREDDY, and GABRIELLE. D on the Indian ocean name list and
F and G on the Australian name list. More cyclones are likely next week.

Cyclone GABRIELLE is no angel and is behaving more like a GABBY or even a
CRABBY and is expected to do a crab-like sidestep to the right towards
Auckland tomorrow.

Yesterday 11 Feb GABRIELLE moved over Norfolk Island, on 11th and peak gust
of NE 102kph at 2:30pm and lowest measured pressure 958.0 at 10pm.

Today GABRIELLE has left the tropics but is still a cyclonic storm so
changes its name for Tropical Cyclone GABRIELLE to Cyclone GABRIELLE. There
is a squash zone of strong winds south of GABRIELLE travelling southwards
across Aotearoa North Island. These winds are strong enough to bring cross
winds gusting over 100km/hr to exposed parts of Hauraki Gulf and close the
Auckland harbour bridge (now) and Auckland airport (on Monday). The cyclone
is staring to de-intensify and estimated central pressure is 967 and rising.

However, on Monday the system is start finding resistance to a smooth SE
path due to a new HIGH east of NZ. The eye is on a wobbling path (like an
out of balance washing machine) and this resistance may coincide with one of
its wobbles strong enough to make GABRIELLE do a sidestep southwards towards
Auckland. As this happens the system may ingest cooler air from the south
and this may cause thermogenesis and allow the system to re-intensify.

Lots of "may" in this outlook and in my illustrated blog at metbob.com is a
meteogram from this afternoon's GFS data for Auckland area.
The time axis is in UTC and estimates the baro (thick black) may drop to 968
on Monday local night. If so, that will be a new record for Auckland. There
is an easterly gale (thin black/ dots for gusts) starting today and easing
from late Monday, and a well-defined peak in the rainfall (blue shading) to
over 20mm/hr on Monday afternoon 6mm/hr=heavy rain).

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is expected to remain active across the Coral Sea /New
Caledonia/Fiji and Tonga to French Polynesia.
Tropical lows may form on the Monsoonal trough north of Australia and non
the SPCZ near Tonga later this week.
Avoid most of the tropics this week as they are looking squally.
However to north of GABRIELLE there is expected to be a zone without trade
winds and that may be useful for getting east.
Travel from Australia is looking ok this week.
It will take until Thursday or Friday before the wind and rain of GABRIELLE
departs from NZ and allows some sailing to or from there again.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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 64 277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

05 February 2023

Bob Blog 5 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.
Compiled Sunday 05-Feb 2023

REVIEW OF THE LAST MONTH (January 2023)
Here is a link to a YouTube clip giving an animated loop of the isobars and
streamlines in the South pacific at

https://youtu.be/7EQXqv6h9J4

Lots of lows formed in the Tasman Sea. And Highs lingered between the South
Island and South of Tahiti. This fed a flow of tropical air from Tonga
towards NZ, as seen in Cyclone HALE on 11 Jan and the event that squeezed
torrential rain out from a line of thunderstorms on 27 Jan.


Sea Surface temperature anomalies can be seen at
psl.noaa.gov/map/clim/sst.shtml
The cool waters of La Nina continue to relax. A severe marine heat wave is
affecting southern NZ, especially Fjordland, bleaching the coral there. This
is starting to show signs of relaxing, see
https://www.moanaproject.org/marine-heatwave-forecast.
There is also a marine heat wave around the Falklands.

Average isobars for past month (below)
In the north Atlantic, west of Spain there has been a swap in pressure
systems from lows to highs. Elsewhere, January's pattern has been an
extension of December's.

Pressure anomolies for past month (below)
The anomaly pattern is much the same as in December, but Lows in the Tasman
Sea in January have been more intense than in December.

Zooming into the NZ area
January has a very similar pattern to December, but the highs near Chatham
Islands have been 5 hPa stronger, and that is what has accentuated the
tropical northerly flow from Tonga to Northern NZ.

TROPICS
There is potential this week for cyclone formation between the south of
Indonesia and the Coral sea.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is expected to be very active across the Coral Sea /New
Caledonia/Fiji and Tonga .
Tonight the SPCZ has a Low L2 south of Niue and this is expected to travel
off to the south-southeast. There is another Low L3 near Vanuatu, and this
is expected to drift southwest and intensify in the Coral sea next few days
and has the potential to then become a tropical cyclone and travel southeast
towards Norfolk Island/northern NZ this weekend. AVOID.
Low L1 (crossing the south Tasman Sea tonight) is a kicker and has
sufficient eastwards momentum to finally push the quasi stationary High (now
near Chathams Islands) off to the east. This may help trigger a pattern
change in the Southern Ocean, allowing another High H2 to travel east across
NZ on Thursday and Friday this week.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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 64 277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

04 February 2023

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