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

31 July 2016

Bob Blog

WEATHERGRAM
YOTREPS
Issued 31 July 2016

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.

Today I open with a point to ponder: what wind was that?
In 1805 Admiral Sir Francis Beaufort put forward an empirical wind scale with 13
units of force (0 to 12), based on the behaviour of the sails on a standard
British Navy frigate from 'just enough to give steerage" to "that which no
canvas sails can withstand".

In 1916 the description was changed from how the sea (fully-developed,
offshore), rather than sails, respond to wind speed and extended to land
observations. George Simpson, (then C.B.E and later Sir), Director of the UK Met
Office, standardized these descriptions in 1923. Today many marine wind
forecasts are not in Bf (Beaufort force) and instead use units such a knots, or
m/s (Russia) or mph (USA). However, the words STRONG, GALE, STORM and HURRCANE
as used in marine bulletins still use thresholds defined by the Beaufort scale

Note that the state of sea table described in the Beaufort scale is NOT used by
meteorologists today. After World War I there was a need for the international
standard in reporting weather, and the code for the 'state of the sea' was
reduced to a 10 point scale (0 to 9). Captain H.P. Douglas of the Royal Navy
designed the Douglas Sea Scale in the 1920s and this still the scale used by
marine meteorologists in today's forecasts.

The Beaufort scale was extended in 1946, when forces 13 to 17 were added to
apply to typhoons. Nowadays only Taiwan and China use these extensions.

When I first estimated the life cycle and attributes of tropical cyclones from
satellite imagery back in the 70s I used the Dvorak technique: see
en.wikipedia.org/wiki/Dvorak_technique. This technique was improved in 2004 as
the ADVANCED Dvorak technique came on line in 2004.

At about the same time the Saffir-Simpson scale was introduced for Atlantic and
Central/Eastern Pacific cyclones (Hurricanes), merging meteorological ideas from
the National Hurricane Centre NHC on storm surge and flooding (Robert Simpson)
with civil engineering estimates of structural damage (Herbert Saffir) so the
hurricanes could be categorized according the wind speed Cat 1 to Cat 5. In
2009 -2010 the NHC made moves to drop the storm surge ranges from the
categories.

There is now a move for cyclones that produce observed wind speeds over 151
knots as category 6. But according to Robert Simpson, there are no reasons for a
Category 6 on the Saffir-Simpson Scale because it is designed to measure the
potential damage of a hurricane to man-made structures. "...when you get up into
winds in excess of 155 mph (135 knots) you have enough damage . if that extreme
wind sustains itself for as much as six seconds on a building it's going to
cause rupturing damages that are serious no matter how well it's engineered"
This reminds me of Admiral Beaufort's original description for his Bf12, "that
which no canvas sails can withstand"
In our part of the world the Bureau of Meteorology introduced the Australian
Tropical cyclone Intensity scale late 1989. I think it is related to the Dvorak
scale, rather than the Saffir-Simpson scale. If I'm wrong, please someone let me
know.
And so these days there are different wind scales in different parts of the
world. The WMO has its job cut out to seek uniformity:

The Tropics
Last weekend DARBY in its dying stages: got close to Hawaii
Things in central and eastern North pacific have eased now (but there are still
a few tropical lows there), and there is just one cyclone at present over
Western North Pacific, namely NIDA which seems to be heading for Hong Kong.
The rain maps, from
trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif ,for the past
weeks shows a few "NW fingers" off the ITCZ relating to tropical cyclones., and
a drop in activity over the central Indian Ocean, no rain at all over the whole
of Australia, and a slight southwards shift in the SPCZ,

WEATHER ZONES

SPCZ=South Pacific Convergence zone.
SPCZ is expected to remain draped from north Coral Sea to north of Vanuatu to
Tokelau to Northern Cooks.
This week's SPCZ may be seen on windyty.com with rain accumulation and ten days.

STR= Sub-tropical Ridge
HIGH in Tasman Sea on Monday is expected to pass over Northern NZ on Tuesday and
Wednesday, then travel off to the east of NZ. Next HIGH, at this stage, is not
expected in Tasman Sea area until Fri 12 August.

Voyage Outlooks:
Tahiti to the west
A trough is expected to pass across Tahiti on local Tue/wed. Avoid those dates
for departure. So if you depart before Tue then you will need to have some
waypoints to sail around this trough. And if you do depart after Wednesday you
will need some waypoints to avoid the strong SE in the enhanced trade winds on
the north side of the HIGH travelling east of NZ.

Between NZ and the tropics
Disturbed SW winds on Monday. Then there is an opportunity to depart as a ridge
passes on Tuesday and Wednesday. But a departure on Tuesday will still encounter
northerly winds from next approaching trough on Thursday.
If you don't mind a few days of waypoint deviations to handle 20 gust 30 knot
northerly winds with up to 4 metres SW swells then you can depart on Tuesday.
Otherwise stay put, and the next opportunity maybe around mid-August.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my yotpak at boatbooks.co.nz/weather.html for terms used.
See my website www.metbob.com for information on tailor-made voyage forecasts
- Feedback to bob@metbob.com.
Tell anyone you like that to subscribe they should email me.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
click FOLLOW at bottom right to subscribe.
To unsubscribe send a reply email saying LEAVE.

24 July 2016

Bob Blog

WEATHERGRAM
YOTREPS
Issued 24 July 2016

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.

I was on my annual vacation last week in Paihia, and now it's back to the
disturbed weather in Auckland.

The Tropics

Last week I mentioned tropical cyclones CELIA, DARBY and ESTELLE, that had
formed in the central and eastern north Pacific. DARBY (156W) and ESTELLE (140W)
are still going and in the past week FRANK (111W) and GEORGETTE (124W) have been
added to the quick forming list. They all seem to be peeling off to the
northwest .

Elsewhere LUPIT (160E) has formed in the northwest Pacific.

And in the Atlantic, it's been quiet since DANIELLE (in June)- which was the
145th consecutive Atlantic cyclone to fail to bring hurricane winds to the
United States. The last cat3 or higher to make landfall on USA was Hurricane
WILMA in Oct 2005 - more than 10 years ago. Then again in the past 10 years we
have had SANDY (Oct 2012, 2nd most costly), IKE (sept 2008, 3rd most costly)
GUSTAV (two weeks before IKE) and IRENE (Aug 2011, 7th most costly). But they
were less than Cat 3 when the made land fall. Meteorologists are investigating
the reasons behind this anomaly. a slight change in the measuring thresholds
makes a dramatic difference in the observations.
See
weather.com/storms/hurricane/news/tropical-storm-colin-extends-united-states-maj
or-hurricane-landfall-drought

or
weather.com/storms/hurricane/news/hurricanes-scale-change-20121128

O, And yes, the most costly was KATRINA (Aug 2005)-- it's 11th anniversary is
coming up.

The rain maps from
trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif for the past two
weeks show a shift of the most intense rain from central Indian Ocean towards
Indonesia, and a build-up in rain intensity around Micronesia.


WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is expected to remain draped from north Coral Sea to north of Vanuatu to
Tokelau to Northern Cooks.
This week's SPCZ may be seen on windyty.com with rain accumulation selected to
ten days.

STR= Sub-tropical Ridge
A weak HIGH cell is expected to spread east across the northern Tasman Sea along
30S on Tuesday and Wednesday, and then again on Sun 31 July/Mon/Tue 1-2 August.

Voyage Outlooks:
Tahiti to the west
It should be a reasonably quiet and dry weak in Tahiti this week - but may be
more unsettled with a passing trough on local Fri 29 July to Tue 2 Aug, so try
and depart before then.
An active trough with squalls and followed by strong SE winds is expected to
affect Tonga around Mon 1 to Thu 4 Aug. Avoid.

Between NZ and the tropics
Disturbed fronts and W to SW winds are expected to cover New Zealand this week
There are three days when these relax-Monday, Wednesday and (sort of) Saturday.
Of these it seems that a Monday departure offers the best opportunity for a
comfortable departure to the north.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

See my yotpak at boatbooks.co.nz/weather.html for terms used.
See my website www.metbob.com for information on tailor-made voyage forecasts-
Feedback to bob@metbob.com.
Tell anyone you like that to subscribe they should email me.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
click FOLLOW at bottom right to subscribe.
To unsubscribe send a reply email saying LEAVE.

17 July 2016

Bob Blog 17 July 2016b

WEATHERGRAM
YOTREPS
Issued 17 July 2016
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.

I'm in mid-winter holiday mode this week in Bay of Islands. Have visited my
nephew's family in Kerikeri today (he's now got a lovely daughter). Will be
visiting Northland radio www.northlandradio.nz on Monday, and the remainder of
week is my own (apart from 18 yachts still on my joblist)

This week I shall comment on the latest readings of the tropical parameters for
El Nino/La Nina as seen at
www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi

This shows that the Southern Oscillation index is now slightly positive-we are
in neutral territory between an El Nino and a La Nina. The climate forecasts
are for a La Nina to kick in during the next few months. If so that should
encourage a northeasterly low between Tonga and New Zealand. Well as you saw in
last week's blog, we have been having that for months now anyway.. So maybe the
seasonal forecast is for more of the same.

Looking at the heat-store in the ocean, a slightly different story may be told.
See www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=nino34&p=monthly
This graph is extended backwards so we can compare the recent large El Nino with
the one in 1998. We can see that the 1998 El Nino as far as the ocean heat-store
was concerned, dove quickly into a La Nina. We can also see that our recent El
Nino was stronger and longer, and is not cooling off as fast. Maybe things
will be slow to change. I suppose that's another way of saying expect more of
the same.

The Tropics
CELIA is set to visit northern parts of Hawaii over next few days, but just as a
low , not a cyclone.
Lining up in the eastern winds for Hawaii are Cyclone DARBY and maybe ESTILLE

We can see from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif
that the eastern north pacific is the breeding ground this month looking at the
weekly rain maps. These also show interesting developments in the South Indian
Ocean and over eastern Australia (brief trough).

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is expected to remain draped from Coral Sea to north of Vanuatu to Tokelau.
A smaller convergence zone is likely to bother the area between Marquesas and
Tuamotu islands this week, and a passing trough should affect Southern Cooks
from local mid-week and move onto Tahiti next weekend.
The trough over Cairns to Mackay tonight is expected to fade over next two days.

This week's SPCZ may be seen on windyty.com, select rain accumulation 10 days.

STR= Sub-tropical Ridge
The weak HIGH over the New South Wales area tonight is expected to stall on
Monday and Tuesday awaiting reinforcements and then travel east across Tasman
Sea on Wednesday and over northern NZ late Thursday early Friday. The next weak
ridge should cross northern NZ on Late Monday/early Tuesday 25/26 July.

Voyage Outlooks:
Tahiti to the West
It should be a reasonably quiet and dry weak in Tahiti this week - but may be
more active next week with a passing trough. As for travelling west, well such
a voyage is likely to encounter that passing trough as some stage, but this is
expected to be minor. From Sat 23 July, as that HIGH travels east of New
Zealand, there may be a squash zone of enhanced trade winds between 20S and
15S.

Between NZ and the tropics
Disturbed SW winds over northern NZ this week, there are breaks in this flow on
Monday, Thursday, and maybe on Sunday. Increasing NW winds on Friday and
Saturday ahead of this week's most active front on Saturday night.

Snow is forecast on State Highway across central North Island tonight for first
time this winter. There is a parameter that measures how far north the SW winds
from the Southern Ocean can get over NZ. It is very blunt the southern Annular
Mode or SAM, and the only measure I can find for it is the AAO (AntArctic
Oscialltion) at
www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/new.aao_index_en
sm.html
, which covers the entire Southern Hemisphere (not just NZ). This tells
an interesting story: that its been positive last few months, has dived briefly
negative mid-July, and is expected to go positive again after today. Not good
for skiing.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my yotpak at boatbooks.co.nz/weather.html for terms used.
See my website www.metbob.com for information on tailor-made voyage forecasts
- Feedback to bob@metbob.com.
Tell anyone you like that to subscribe they should email me.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
click FOLLOW at bottom right to subscribe.
To unsubscribe send a reply email saying LEAVE.

10 July 2016

Bob Blog 10 July

WEATHERGRAM
YOTREPS
Issued 10 July 2016
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.

The weather patterns averaged over the last month show an interesting
enhancement of the subtropical ridge from Africa to SW of Australia and from NZ
to southern South America. The resulting anomalous anticyclonic northerly flow
over New Zealand led to June being a warm month. The lower than normal pressures
around Antarctica has been giving a strong positive Southern Annular mode (SAM)
- strengthening the westerly winds and swells around the Southern Ocean. And
there has been a breeding ground of Lows west of UK in the North Atlantic month
since March -- no wonder Wimbledon has been so wet this year.

Averaged isobars for June, and their deviation from norma are seen at
www.esrl.noaa.gov/psd/map/images/fnl/slp_30.fnl.anim.html and
/slp_30a.fnl.anim.html

Tropical cyclones are becoming damaging. NEPARTAK was cat 5 when it crossed
Taiwan and is now weakening over eastern China.BLAS is still travelling west
near 20N 135W and now fading, and is being followed by CELIA which may travel
all the way to Hawai'i between local 17 and 19 July. Brace if it does.

Last fortnight of weekly rain profiles, as seen at
trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif,
shows how the Intertropical convergence zone is remains strong over the eastern
pacific. Also there is intense rain over south China and Southeast Asia.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is expected to remain draped from Coral Sea to north of Vanuatu to Samoa
and at times to the Palmerston Island /Niue area. There is also likely to be a
developing trough near the northeast end of Australia by the weekend.

STR= Sub-tropical Ridge
The HIGH which has formed to east of the South Island is held dynamically
together is the LOW on its northern side between NZ and Tonga. There is a strong
squash zone between these systems. These should travel east this week to 160W as
a tied-pair relationship, with HIGH near 45S and low near 30S until end of the
week when the low weakens.

New HIGH is expected to travel east along around 36S across Bass Strait area on
Saturday and then slowly cross the Tasman Sea by Tuesday 19 July.

Voyage Outlooks:
Tahiti to the west
A PASSING TROUGH offers a challenge with NE/N winds on its eastern side, and a
period of S/SW winds on its western side, and some squalls in-between. The winds
associated with this trough are expected to be less than strong, so this may be
an acceptable challenge perhaps. OR what until after Friday 15 which is when the
trough should go by the Borabora area, for a less complicated passage.

Between NZ and the tropics
The Low between NZ and Tonga is travelling slowly east along 30S, with a strong
squash zone on its south side. Too much SE swell for comfort on Monday.
Tuesday is looking to be a good compromise departure, and possibly Wednesday.
On THURSDAY an active front is expected to cross NZ from the Tasman Sea followed
by a day or so of strong and squally SW winds maybe until Saturday or Sunday,
stay put for that. Then there may be a good weather pattern departure by Mon 18,
perhaps Sun 17 July.

Between Australia and New Caledonia/Fiji
An active trough is expected to affect south of 30S on Monday to Friday, and
weather may be OK for a departure from Brisbane to New Caledonia on Monday or
Tuesday, but after that may as well stay put.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my yotpak at boatbooks.co.nz/weather.html for terms used.
See my website www.metbob.com for information on tailor-made voyage forecasts-
Feedback to bob@metbob.com.
Tell anyone you like that to subscribe they should email me.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
click FOLLOW at bottom right to subscribe.
To unsubscribe from WordPress: click the "unsubscribe" link on the bottom of the
email.
Or, if email wasn't from WordPress then send a reply email saying LEAVE.

03 July 2016

Bob Blog 3 July 2016

WEATHERGRAM
YOTREPS
Issued 3 July 2016
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.

Back in the early 70s when I was a university student working at New Zealand
Meteorological Service I was asked to help Edith Farkas with her study of
observations of deplenishing amounts of ozone in the stratosphere. She was a
good example of how it was possible to be a woman meteorologist in New Zealand
even then---
See www.iwonderweather.co.nz/taxonomy/term/188
These studies resulted in the Montreal Protocol in 1987 whereby the UN banned
the use of CFCs as a refrigerant. The Ozone hole peaked in 2000, and has had
minor drops ever since, increasing briefly in October 2015. A news release this
week announces that new studies of the data shows that increase was caused by
the eruption of the Chilean Volcano Calbuco, and the hole is actually on "a path
to heal". The Montreal protocol is a beacon of hope for us humans on this
planet, a sign that we can indeed terraform beneficially.
See m.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11666732

This year is turning out to be the warmest on record--- a good discussion on
this and other weather topics is given by MetService Severe weather forecast
Eric Brenstrum at
www.radionz.co.nz/national/programmes/nights/audio/201806090/nights'-science-wor
ld-weather



Tropical cyclones are starting to form.
AGATHA and BLAS are storms in the northeast Pacific that have formed on the
Intertropical Convergence zone west of Mexico. These two storms are expected to
go off to the northwest, but they may be followed by a third storm forming this
weekend that may go westnorthwest all the way to Hawaii area by end of next
week.
And NEPARTAK is a storm in the NW pacific to south of Guam moving northwest
towards Taiwan.

Last fortnight of weekly rain profiles as seen at
trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif
shows how the Intertropical convergence zone is now intensifying over the
eastern pacific.
Also there is intense rain over south China and Southeast Asia.


WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is expected to remain draped from Coral Sea across northern Vanuatu to the
Tuvalu/Tokelau area, then to Northern Cooks/Marquesas. There is also likely to
be a developing trough near the end of the week over the Tahiti area.

STR= Sub-tropical Ridge
STR is weak and well to the north.
The HIGH that is north east of NZ of Monday is expected to travel east along
30S. There may be a small squash zone of enhanced Se winds on its northern side
near 18 to 19S between Palmerston Island and Tonga from Tues to Thursday UTC.
The next HIGH to exit Australia may be at 45S late this week, travelling east
across southern and central NZ this weekend. It may indeed have a squash zone
on its northern side, over or near northern NZ.

Voyage Outlooks:
Tahiti to the west
Looks OK for departure to the west between now and Tuesday local, albeit with
light winds for starters. After that a developing trough is expected to bring
some squalls and increase the SE winds to over 20 knots.. May have to wait until
20 July for next window of appropriate weather.
Since the SPCZ is expected to remain north of 15S, it appears that a voyage to
the west should travel along the drier and more settled latitudes near 17S.
Weather may not remain settled all the way from Tahiti to Tonga, as a trough is
expected to affect the Tongan area from 10 to 12 July local.

Between NZ and the tropics
MAYBE NOT this week (again), may as well stay put (again). A fast boat can
possibly depart from Opua on Monday (after a passing low) but is likely to
encounter strong + winds from a front on Thursday.
A LOW is crossing northern NZ on Thursday and Friday and is expected to linger
to north of NZ until next week. The northerly winds ahead of this low are
expected by Wednesday. So it's another stay put week.

Between Australia and New Caledonia/Fiji
OK to depart from Coffs/Brisbane area on Monday (local), but otherwise stay put
for a trough is expected there on Tuesday deepening into a LOW off Sydney
rapidly on Tuesday night. Stay put Tuesday to Thursday local then it may be OK
to go.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my yotpak at boatbooks.co.nz/weather.html for terms used.
See my website www.metbob.com for information on tailor-made voyage forecasts-
Feedback to bob@metbob.com.
Tell anyone you like that to subscribe they should email me.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
click FOLLOW at bottom right to subscribe.
To unsubscribe from WordPress: click the "unsubscribe" link on the bottom of the
email. Or, if email wasn't from WordPress then send a reply email saying LEAVE.

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