Translator

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

29 December 2013

BOBGRAM issued 29 Dec

WEATHERGRAM
YOTREPS
Issued 29 December 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless
otherwise stated.

SOI
The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over
the South Pacific as one number. It is based on the standardized difference in the
barometer readings between Tahiti and Darwin.
SOI has dropped recently and is now hovering around zero. Its 30-day running mean was
minus 0.02 on 29 Dec.

MADDEN JULIAN OSCILLATION MJO
The MJO is the name given to a detectable pattern of increased convection ion the tropics
that travels from the Indian Ocean to the Pacific Ocean.
See http://en.wikipedia.org/wiki/Madden%E2%80%93Julian_oscillation
Its arrival in the western Pacific is associated with Tropical cyclone formation. The
amount of tropical convection can be traced by measurements (from satellite) of the
Outgoing Longwave Radiation OLR. Latest pattern in the OLR seems to show a quietening of
the convection in the South Pacific AFTER A possible burst of activity mid this week
around Fiji/Samoa/Tonga

TROPICAL TOPICS-
Tropical Storm SIX is to the NE of Madagascar moving to the south, and Tropical Storm
CHRISTINE is near the NW coast of Australia and expected to travel S and SE taking rain
into the interior of Australia /reducing the recent heat wave in Western Australia.
In the recent past some models were picking a possible tropical LOW to develop over Fiji
by 1 Jan. However, the convection in the Coral Sea has dried out over the weekend and the
current expectations are this development nay be delayed until 8 January (GFS model)-or
may occur south of Tonga/Niue near 25S (ECWMF model) . Things are in flux so keep watching
the local daily updates.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ seems to have dried out over the Coral Sea recently and is in a northern position
over Tuvalu and Tokelau with a weaker zone over Samoa and Tonga. It is expected to
activate over Samoa/ Tonga/ Niue by 1 January.

Sub-tropical Ridge STR
The blocked HIGH that is near 40S to south of French Polynesia and should stay put this
week. Another High is expected to move into the Australian Bight, but will now have to
wait until after 4 Jan as the remains of CHRISTINE work their way out to the ESE. This
leaves the Tasman Sea and NZ in a troughy area, between anticyclones, this week.

Tasman Sea /New Zealand
Troughy. The front that knocked 5 yachts out of the Sydney-Hobart race is expected to
cross NZ on Mon followed by a weakening trough on Wednesday and then another active
front/low on Fri/Sat, and then, early next week, the remains of TC CHRISTINE combined with
another Low from the Southern Ocean.
There may be the odd day here and there worthy for fishing, sailing, swimming, especially
in the north, but it does not look like there will be any extended period of settled
weather this week for holidaying.

However, please let me give you an you a not-so-familiar verse to the familiar refrain for
the New Year

We two have paddled in the stream,
from morning sun till dine;
But seas between us broad have roared
since auld lang syne.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to
subscribe.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Website is at metbob.com. Feedback to bob@metbob.com

22 December 2013

BOBGRAM issued 22 Dec

WEATHERGRAM
YOTREPS
Issued 22 December 2013
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 of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated
SOI The Southern Oscillation Index SOI (30 day running mean) sums up the
weather pattern over the South Pacific as one number. It is based on the
standardized difference in the barometer readings between Tahiti and
Darwin.
SOI is currently steady after a recent rise. Its 30-day running mean was
0.66 on 22 Dec.

The Ocean: The warmer the sea the quicker it evaporates, tossing water
vapour into the air, where is rises and cools into cloud. The equatorial
Pacific region hosts the warmest sea on the planet. Thus its sea surface
temperatures SST may be thought of as a factor in the running of planetary
weather engine.

Sea surface temperatures are now warmer than normal at Galapagos. But NOT
along the Peru Coast. This Peru Coast deserves special scrutiny during
December =96 because it is the arrival of warmer-than-normal water every
so often there in December that triggers the onset of an El Nino episode-
El Nino gets its name for the El Nino di Navidad (Christmas) festival in
Peru. This warm-water-arrival is NOT happening there this December.

TROPICAL TOPICS
Tropical cyclones AMARA and BRUCE formed in the India Ocean in the past
week as predicted in Weathergram issued last Sunday. They are moving SW
and expected to recurve to the SE at 20s. They have been formed from an
area on enhanced convection that is moving slowly east from the NW Indian
Ocean onto the Timor Sea during the next week or so. This pulse of extra
convection may continue eastwards and reach the northern Coral Sea area
early in the new year, increasing the chance of development there of
tropical depressions

WEATHER ZONES
As a Christmas present to any budding meteorologists on my list , I'd like
to share with you a cool Website for viewing the wind flow of the GFS
model at various levels on a weird collection of map projections go to
earth.nullschool.net, click on the word earth and then play with the
variations. Have a happy meteorological Christmas!

South Pacific Convergence Zone SPCZ
The SPCZ is in its normal position roughly between Solomons and
Fiji/Tonga.
A subtropical low is expected to form on the SPCZ over or around Fiji by
Friday 27 Dec and move across Tonga on Sat/Sun /Mon/Tuesday. Avoid

Sub-tropical Ridge STR
The STR is near its normal solstice position over the Australian Bight but
is currently weak and more fluid over the Tasman Sea/NZ area. On Boxing
Day and the following days a cold dry HIGH is expected to move NE out of
the Southern Ocean (south of NZ) and to the east of NZ and then east along
45S next week.

Tasman Sea /New Zealand
The Low that is over Tasmanian tonight is expected to deepen as it crosses
the Tasman Sea on Monday and then onto southern NZ on Tuesday. This
should trigger a new low to form off the Canterbury coast on Christmas Eve
and then travel NE to north of Chatham Islands on Christmas day. This
scenario brings a transition of wind flow over NZ from NW on Tuesday to W
then SW then S then SE for Boxing Day and then E for Friday. At some
stage in this transition there may be an OK period for having that
Christmas BBQ, but it will come and go, and some fine-tuning may be
needed to get the timing right.
See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at
bottom right to subscribe. Weathergram text only (and translator) is at
weathergram.blogspot.co.nz
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15 December 2013

BOBGRAM issued 15 Dec 2013

WEATHERGRAM
YOTREPS
Issued 15 December 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

SOI The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin.
SOI is currently steady after a recent rise. Its 30-day running mean reached 0.75 on 15 Dec.

TROPICAL TOPICS
The Indian Ocean is expected to be a place o0f tropical action this week. There is already a depression near 15S 80E moving west. On Monday another tropical low is expected to form near 8S100E and this one has a good chance of growing into a tropical cyclone.
This activity is related to a pulse of increased tropical convection in the Eastern Indian Ocean, So far, this extra convection seems to be staying put, however it is also likely to start travelling east onto northern Australia by the end of this week or next week and , if so, then it may reach the Coral Sea and tropical dateline areas by the end of December or early January, increasing the chances of development of tropical depressions.


WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is in its normal position roughly between Solomons and Fiji with a side branch between Tuvalu and Northern cooks. It is expected to become active over Fiji and Tonga from Friday 20 to Monday 23 Dec, developing a small depression on Sunday.
A subtropical low is forming south of the Southern Cooks and is expected to travel south over the next few days, stealing away the winds over the Cooks.
The cricket players in Perth are enjoying the inflated temperatures found in a heat trough, and playing for the ashes.

Sub-tropical Ridge STR
The STR is also near its normal position as we approach the longest day (next Saturday). It is strong across a wide longitude belt and there are strong SE winds on its northern side over the Coral Sea and occasionally over New Caledonia. This makes it very hard to sail from Noumea to NZ this week.

Tasman Sea /New Zealand
Over the North Island this is a week of passing anticyclones—but there is cold air aloft so the convergence zones formed between these passing highs are likely to trigger daytime convection. OK for sailing because most of the convection is inland or coastal rather than over the sea.

Over the South Island there are occasional passing troughs, especially on Monday/Tuesday and Thursday, and Lows, especially on Sat/Sun. Because of NZ's terrain these feature bring days of strong wind to the Cook Strait area.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
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08 December 2013

BOBGRAM issued 8 Dec 2013

WEATHERGRAM
YOTREPS
Issued 08 December 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Last week I commented how the International Research Institute of Columbia University have looked at the plume of 24 ENSO models and shown that the probability of an El Nino event MAY increase to over 50% by mid-2014. I should reiterate that at present there are no signs that this is actually happening yet.
However, the term El Nino comes from the festival of El Nino de Navidad (Christmas) – and gets this naming because this climate variation often starts out with the arrival of warmer than normal sea along the Peru Coast during December. There does indeed seem to be some warmer sea along the Peru Coast at present—but cooler sea around Galapagos, so we have something like a mixed bag at present.

SOI The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin.

SOI is currently on a rising trend and its 30-day running mean reached 0.7 on 8 Dec. So the current trend is towards the La Nina side of things.

TROPICAL TOPICS
TC MADI is travelling north towards the east coast of India , so the Northern hemisphere cyclone is still open.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is now returning to its normal position and is expected to visit Fiji and Tonga on Monday/Tuesday/Wednesday this week. Another branch of the SPCZ should remain slow moving over Samoa/Tokelau to Northern Cooks.
A Monsoonal trough or heat trough is forming over northern and NE Australia this week and is expected to cause strong northerlies along the east coast on Monday and Tuesday. The low that is expected to bud off the eastern seaboard of Australia on Wednesday should reach NZ on Thursday as a trough.

Sub-tropical Ridge STR
The STR is now returning to a more normal latitude of 30S in the South Pacific, but is constrained to its summer position of the Australian Bight by the heat trough over Australia.
Another High is likely to move northeastwards from the south and east of NZ starting Tuesday 10 Dec and continuing across the South Pacific, getting to 40S south of French Polynesia by Tuesday 17 December.

Tasman Sea /New Zealand
Low is expected to move away from southern NZ on Monday, followed by light winds over the North Island.
Next trough is expected to be intense over the South Island on Thursday and less intense over the North Island on Friday 13th, followed by a period of S/SW winds.
A weaker trough is expected to cross NZ on Sunday 15 December followed by a HIGH over the central and southern parts (E or SE winds for Northland).

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Website is at metbob.com
Feedback to bob@metbob.com

01 December 2013

BOBGRAM issued 1 Dec 2013

WEATHERGRAM
YOTREPS
Issued 01 December 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

SOI
The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin.
It reached a high of 0.52 on 22 September, and since then has dropped and bounced. On 24 November it has a 30-day running mean of plus 0.3, and is trending upwards.
The International Research Institute of Columbia University have now produced data that looks at the plume of 24 ENSO models and shows that probability of an El Nino event is likely to increase to over 50% by mid-2014. This may well impact on your sailing voyages next year so be aware of this as you do your preparations.

The Ocean:
The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. Anomalies tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet.
In September and October all seemed to be around normal, but at present there seems to be a warming trend west of the dateline and a cooling trend further east.

TROPICAL TOPICS
TC Alessia went inland and then west across Northern territories where it dropped its rain and ran out of puff. It reminds us that the Cyclone season for the South Pacific is now OPEN.


WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ continues to be north of its normal position, rather weak and somewhat disjointed. It is expected to gain intensity over the northern Coral Sea this week is in its northern most position at present and may spread south to visit Fiji and Tonga from 7 December.

Sub-tropical Ridge STR
The STR continues to be strong and south of normal in the zones east of NZ and over Southern Bight of Australia with large blocking Highs that have been a feature all during November. However it continues to be weak in the Tasman Sea/NZ area. There is a natural tendency for lows to form on the NW shoulder of a blocking high, and sure enough one has formed today in between New Caledonia/ New Zealand /Lord Howe/ It is under an upper trough that is about to bud off and so it is expected to slowly go SE and then south.

Tasman Sea/NZ.
That low should slide southwards to west of NZ in a dying state on Wednesday and Thursday, and then be followed by a more aggressive trough/Low combo from the west crossing NZ on Friday and Saturday.

Briefings
Between tropics and NZ
Slack winds for starters this week as the Tasman Low moves slowly off, stealing the wind. Then a useful northerly flow from Thursday onwards around the developing High east of NZ as it travels off to the NE.
The next trough to more onto NZ is currently expected maybe around 12-13 Dec. This system may only affect central and southern NZ, but be aware that could affect northern NZ and if so try not to arrive there at the same time.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Website is at metbob.com
Feedback to bob@metbob.com

24 November 2013

BOBGRAM issued 24/25 Nov 2013

WEATHERGRAM
YOTREPS
Issued 24 November 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Thanks to the yacht people at Opua who came along on Friday and allowed me to share with them my ideas, and for the feedback they gave me regarding my weather forecasting. Thanks also to those in Gulf Harbour who fed and watered me this Sunday evening. All appreciated.

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is the NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet.
This parameter has been near average so far this year, slightly on the cool side.

TROPICAL TOPICS
The first cyclone for the southern hemisphere's new cyclone season is TC Alessia and is moving east inland near Darwin over next few days.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is in its northern most position at present and rather weak and disjointed, but it is expected to activate this week and drift slowly south onto Samoa by early December.

Sub-tropical Ridge STR
The STR is now oscillating between its southern latitude band and its northern latitude band. That High which is expected to be over Aussie Bight by Wednesday should move NE into the Tasman Sea by Sunday/Monday, bringing some settled weather to the Tasman Sea area after rather unsettled weather there this week.

Tasman Sea/NZ.
Front in the Tasman Sea is expected to cross the North Island on Wednesday bringing some welcome rain after a dry spell, and this is expected to be followed by a Low. Another weaker trough is expected to cross the North Island on Sunday 1 December, followed by settled weather of a High.

Briefings
Between tropics and NZ
Slack winds for starters this week—then a useful northerly flow from Monday to Wednesday, then a warm front on Wednesday/Thursday, then slack winds again—So weather pattern is not the best for getting from tropics to NZ this week, but if you don't mind doing some motoring and going through a warm front at some stage, then the voyage can be done.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Website is at metbob.com
Feedback to bob@metbob.com

17 November 2013

BOBGRAM issued 17 Nov 2013

WEATHERGRAM
YOTREPS
Issued 17 November 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

SOI: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin.
It reached a high of 0.52 on 22 September, and since then has dropped. On 17 November it has a 30-day running mean of -0.3, and is trending downwards.

TROPICAL TOPICS
Things seem to have gone quiet at present – no tropical cyclones today.
An interesting comparison of the geographical extent of TC HIAYAN with that of TC KATRINA can be seen at http://lnk.ie/KWJT/e=bobmcd1.bobgram@blogger.com/http://tropic.ssec.wisc.edu/temp/Geographical-Coverage-Hiayan-vs-Katrina.jpg

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ has retreated to it more northern position in the past week and is now expected to go through a quiet period for the next week or more.
A Low is expected to form in a trough that is crossing New Caledonia on Monday. This Low should then deepen between Fiji and NZ on Tuesday and Wednesday. On Thursday its associated trough should cross Fiji and on Friday it should cross Tonga. Following this trough there may be a few days of light variable winds over New Caledonia until Friday and over Fiji until Saturday and Tonga until Sunday 24 November.

Sub-tropical Ridge STR
The STR went to the southern limit if its travel last week and is expected to stay well south of normal this week. This is a pattern sometimes called 'low index' and gives plenty of room for lows to form and expand between the SPCZ and the STR. This is exactly what is expected to happen this week with a low deepening between Fiji and NZ.

Tasman Sea/NZ.
High over the South Island is expected to travel off the east on Monday/Tuesday maintaining a NE flow over NZ. Low between NZ and Fiji should reach peak intensity near 28-29S 175-179E on Wednesday and then weaken as it moves off to the southeast.
Trough in the south Tasman Sea is expected to cross the South Island on Thursday and then fade away as it travels off to the east in Friday. This is likely to be followed by light winds for a few days.

Briefings
Between tropics and NZ
The Low between Fiji and New Zealand and the trough and light winds that follow it basically closes down the idea of getting a cruisey sail to NZ this week. Some may want to get going in the light winds that follow, but others will prefer to wait for some steady and useful breezes to return – maybe this weekend or early next week.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Website is at metbob.com
Feedback to bob@metbob.com

10 November 2013

BOBGRAM issued 10 Nov 2013

WEATHERGRAM
YOTREPS
Issued 10 November 2013

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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

XTRA are disabling my bobmcd@xtra.co.nz account every time I send a weathergram blog now. Very inconvenient so I think I'll change the sending address to bob@metbob.com slowly over the next few weeks. Those who have bobmcd@xtra.co.nz white listed on their sailmail or winlink accounts (on list of allowable emails):- please also white list bob@metbob.com , thanks- easiest way to do this is to send an email from your account to bob@metbob.com .

SST: The Sea Surface temperature anomaly is a good indicator as to where the weather may behave 'normally' or 'abnormally'. The latest anomaly map over the South Pacific shows an inter-lace of cool and warm areas along the equator between the dateline and Peru. This is the zone that triggers an El Nino or a La Nina but it isn't quite doing either at present.

There is a zone of 'warmer than normal' covering the region from Solomons across Fiji to Tonga. This might help tropical cyclones to form or offer them a track to follow. Too early to tell, but keep this in mind.

TROPICAL TOPICS
TC HAIYAN was heralded as the world's strongest typhoon of the year before it made landfall in the Philippines, and now the death toll from this storm is estimated to be over 10,000 with over 4 million people being affected by this one day event. It is now losing intensity and turning north and should fade over south China in the next few days.

(Add a couple of 'r's, and then 'Terror' is a meteorologist's middle name.)

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is slowly getting more active and stretches from Solomons to Wallis/Futuna/Samoa to southern French Polynesia, with a few side branch convergence zones CZ. A Low is expected to form in the CZ crossing Southern Cooks this weekend producing a squash zone of reinforced easterly winds near 30S from 140 to 160W early next week.

Sub-tropical Ridge STR
After last week's steady progression of highs and Lows in the mid-latitudes, the STR spent last week travelling south, and is now in its southern setting. This is a pattern sometimes called 'low index' and is expected to continue this week as well, with plenty of room for lows to form between the SPCZ and the STR.

Tasman Sea/NZ.
A Low is now expected to form within the heat trough over Australia and move across 30S on Sunday 17th and deepen near Lord Howe Island early next week. A front associated with its trough is expected to reach New Caledonia by Monday 18 Nov and maybe Northland by Wednesday 20th November, preceded by strong NE winds. Avoid.

Route Briefings
Between tropics and NZ
Try and time your voyage from the tropics so the arrival tine in New Zealand does NOT coincide with a front or strong winds.
The current pattern looks promising- High pressure over NZ from now until Monday 18th Nov are expected to maintain much the same pattern with a flow that is SE/E flow over New Caledonia /Fiji/Tonga and a weaker NE to Opua. Good for departures on Monday and Tuesday.

However it is not expected to last this way for long.
A LOW is expected to move from central Australia to the Lord Howe area on or by Sunday 17 Nov, and may become slow-moving there next week. An associated FRONT is likely to reach New Caledonia by Monday 18 Nov and Northland by Wednesday 20 November. The NE winds ahead of this front may aid your voyage, but not if they get strong. Still too far away to tell exactly.

Since the sailing time for a boat capable of going up to 6 knots in the likely winds for this voyage from tropics to NZ is around 7 days to Opua, a departure on Tuesday 12th or early on 13th may get you to Opua before the front on the 20th, but a later departure may have an encounter with strong winds from that front. This is all still rather hazy, so ask for an update.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Website is at metbob.com
Feedback to bob@metbob.com

03 November 2013

BOBGRAM issued 3 Nov 2013

WEATHERGRAM
YOTREPS
Issued 3 November 2013

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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Another quick Weathergram this week.

Last week XTRA changed their email server settings and only allowed bobmcd@xtra.co.nz to send 200 of these emails to my email list of 620. So I resent via bob@metbob.com but several of you do not have that address set on their white list of allowable emails, and would have missed out. I'm hoping tonight's edition gets to you all.

SOI: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin.

It reached a high of 0.52 on 22 September, and since then has dropped to around zero. On 3 November it has a 30-day running mean of -0.16 , close to zero.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is expected to spend most of this week north of 15S.

Sub-tropical Ridge STR
The STR has weakened to a few lines mainly along 25S. Between 25S and 45S the South Pacific this week has a near regular steady progression of Highs and Lows, all mainly travelling along 40S.

The Low which is expected over North Island on Wednesday should travel off to the southeast and weaken.

The next High from the west is expected to travel across Tasmania/South Tasman Sea on Mon 11 Nov. This High is then expected to intensify over or just east of NZ early to mid-next week, 12-15 November, and form a squash zone of strong easterly winds between NZ and Fiji /Tonga for a few days. Avoid.

Route Briefings
Between tropics and NZ

Try and time your voyage from the tropics so the arrival tine in New Zealand does NOT coincide with a front or strong winds.

The Low crossing the North Island during mid-week has OK winds in its trough between NZ and the tropics—except that some swell over 3 metres may get as far north as 25S on 6 November.

From 12 November onwards (mid next week) some strong easterly winds are likely between NZ and the tropics because of the squash zone of the north side of a large High. It's too far away to tell exactly at this stage, but this needs to be taken into account by anyone wishing to depart from the tropics late this week, heading for NZ.

See my yotpak at http://lnk.ie/KFRS/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Website is at http://lnk.ie/KFRT/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

27 October 2013

BOBGRAM issued 27-28 October 2013

WEATHERGRAM

YOTREPS

Issued 27-28 October 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Only time for a quick Weathergram this week

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is expected to spend most of this week north of 15S.
A squally low has developed over the Kermadecs area tonight and is moving off to the Se trailing behind a small trough that is fading away.
A low is expected to form offshore of Sydney on Monday/Tuesday and deepen as it crosses the Tasman sea on Wednesday/Thursday and New Zealand on Friday. Avoid. A southerly flow is likely to cover the NZ area and the area to north of NZ after this Low on Friday/Saturday/Sunday 1/2/3Nov, may be longer. Avoid.

Sub-tropical Ridge STR
The STR is expected to remain strong along 30 to 35S this week, and that means only mildly enhanced trade winds on the north end of the traveling highs.
One high is expected to move east along 32/35S from near NZ on Monday 28 October to 120W by Monday 4 Nov.
The next High is expected to form in the Tasman Sea from Friday 1 Nov and fade in the north Tasman Sea by Mon 4 Nov.

Route Briefings
Between tropics and NZ
Try and time your voyage from the tropics so the arrival tine in New Zealand does NOT coincide with a front or too much of a southerly flow—since the NZ area is likely to have a southerly flow for at least 1/2/3 Nov and maybe also 4/5/6 November, Tuesday 29 is the best day this week for departure

See my yotpak at http://lnk.ie/K7MU/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is metbob.wordpress.com
Weathergram text only and translator is weathergram.blogspot.co.nz
Website http://lnk.ie/K7MV/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

20 October 2013

BOBGRAM issued 20 Oct 2013

WEATHERGRAM
YOTREPS
Issued 20 October 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

The Palolo are rising
For those lingering in the South Pacific until the end of the month : you may be in for an interesting delight this weekend with the waning moon, especially around the third quarter- when the tide starts ebbing just before dawn. In October or November this usually triggers a spawning of a coral worm called Palolo (or Balolo in Fijian). Sometimes this may be large enough to colour the sea – stuff can be netted and eaten raw or cooked. Ask the locals.

The South Pacific cyclone season:
The scientists in NZ, Fiji and Australia have issued a report about what to expect in the South Pacific for the cyclone season Nov 2013 to April 2014. They expect a near average numbers over the region as a whole (8 to 12), with increased activity late in the season.

Where to get weather information?
Last week this blog gave a few websites but the Group Mail server I am using distorted them so they didn't work. I'll try again here.
For the ECMWF model try bit.ly.ecoz
For the MetService view of the UK model try bit.ly/7daywx
For swell maps try swellmap.com
Even if you only have e-mail access you can request some text based Internet products thanks to saildocs. Send an email, no subject needed , to query@saildocs.com with one of these messaged:
For warnings : SEND http://lnk.ie/JV6J/e=bobmcd1.bobgram@blogger.com/http://m.metservice.com/warnings/marine
For high seas: SEND http://lnk.ie/JV6K/e=bobmcd1.bobgram@blogger.com/http://www.met.gov.fj/aifs_prods/10140.txt
For Fiji Marine :SEND http://lnk.ie/JV6L/e=bobmcd1.bobgram@blogger.com/http://www.met.gov.fj/aifs_prods/10060.txt
For Tonga Marine: SEND http://lnk.ie/JV6M/e=bobmcd1.bobgram@blogger.com/http://www.met.gov.to/index_files/routine_forecast.txt

TROPICAL TOPICS
Things remain busy in the Northern Hemisphere tropics with TC FRANCISCO skirting southern Japan. TC RAYMOND is off the west coast of North America and is not expected to make landfall. . Tropical depressions 01F and 02F, the first two of this new season, are being watched by the Fiji Met Service tonight. More about them soon.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is activating so that TD01F has appeared on it between Solomons and northern Vanuatu as an open trough area. Also TD02F has appeared as a closed isobar centre to southwest of Funafuti. TD01F is expected to fade away on Monday and TD02F is expected to go S and SE then convert into a dose of very squally weather moving across Fiji on around Tuesday 22 Oct UTC. It is the expected to take an active part of the SPCZ onto Tonga on Thursday and Friday UTC and then onto Niue on Saturday/Sunday UTC. Avoid.
During Sat/Sun the trough near Niue is expected to link with a front from NZ and form a large slack trough of light winds over the Kermadecs area
Another branch of the SPCZ is lingering along 5 to 8S across Northern Cooks.

Sub-tropical Ridge STR
The STR is expected to remain strong along 30 to 32S this week, and that means enhanced trade winds on the north end of the traveling highs.
One high is expected to move east along 32S from NZ to 120W between Monday and Friday.

The next High is expected move from Australian on Saturday 16 Oct across the Tasman Sea at 33S and then the North Island by Tue/Wed 29/30 Oct.

NZ/Tasman Sea
This area continues to have periods of unsettled weather with enhanced winds south of 35S, especially in between the high cells of the STR. Thursday 24 to Monday 28 Oct is expected to be one of these periods, right in time for Labour week- a long holiday weekend celebrated in NZ. A front is expected to cross northern NZ on Friday night, proving an interesting challenge to those involved in this year's Coastal Classic from Auckland to Russell in the Bay of Islands. This front is expected to be followed by W/SW winds until late on the holiday Monday, good for the return home.

Route Briefings
Tahiti to Tonga:
A trough is lingering to east of Tahiti at present but should fade. The STR is maintaining useful trade-winds all the way to Tonga at present, but that trough reaching Niue on Sat/Sun 26/27 UTC may change this.

Between tropics and NZ
Looking OK to depart when the SPCZ in not visiting. For Fiji this is on Wednesday/Thursday/Friday, and from Tonga this is Monday /Tuesday/part of Wednesday.
After the SPCZ visits Tonga on Thursday and Friday a large slack trough is expected to form near the Kermadecs and that may delay departures from Tonga for a while.
Avoid arriving in New Zealand when a front crosses on Friday 25 UTC or the next front on Thursday 31 Oct.

Between New Caledonia and Australia
A trough is expected to be crossing the eastern seaboard of Australia around Tue/Wed/Thu 22/23/24 and another on Tue/Wed 29/30 Oct. Avoid arriving on these dates.

See my yotpak at http://lnk.ie/JV6N/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/JV6O/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/JV6P/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/JV6Q/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

13 October 2013

BOBGRAM issued 13 Oct 2013

WEATHERGRAM
YOTREPS
Issued 13 October 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Apologies to those who get this twice--- server is changes settings on me and I have to do a resend part way through.

Where to get the best weather?
If you are planning to sail from Tonga/Fiji/Vanuatu/ New Caledonia to NZ in October/ November, and looking to buddy with someone, then you may be interested in checking out the ICA's "All Points Rally" to Opua, see http://lnk.ie/JO19/e=bobmcd1.bobgram@blogger.com/http://www.islandcruising.co.nz/
Some sailors have asked me recently how good are the grib files they are downloading. Well, most of you are looking at data gleaned from the GFS model, and it's good, but not the best. A study done in 2012 shows ECMWF is usually the best. Grib data for EC is not easily available but when you have Internet you can check its latest for the next 10 days for http://lnk.ie/JO1A/e=bobmcd1.bobgram@blogger.com/http://bit.ly.ecoz
Second best is the UK model, again its grib data is not easily available, but MetService pick the model of the day to feed their regional model , and it is usually EC or UK that they pick, and then it is further processed to give maps at http://lnk.ie/JO1B/e=bobmcd1.bobgram@blogger.com/http://bit.ly.7daywx
So check these web sites when planning your trip (and add http://lnk.ie/JO1C/e=bobmcd1.bobgram@blogger.com/http://www.swellmap.com to look at the likely swells). And if your grib data agrees with these then all is good, but if not then you need to consider multiple scenarios.

TROPICAL TOPICS
It is a busy time in the Northern Hemisphere tropics with TC PHAILIN being the largest and most intense cyclone to make landfall from Bay of Bengal into India in the last 14 years. TC OCTAVE is off the west coast of North America and re-curving towards Baja California. TC NARI is about to travel from east to west across the Philippines and head for China, and TC WIPHA seems to making a bee line for Japan.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ has been taken to the north of its range by that active squally trough which brought a S/SW change to Fiji/Tonga last Thursday night (as mentioned in my weathergram last week). During this week is should slowly drift south again, reaching Fiji and Samoa by the weekend. ECMWF model has a low forming on the SPCZ near Fiji early next week, and GFS mode, in a run dome today, has a deep low over Vanuatu early next week. Too far away to be sure at this stage, but something to keep aware about.

Sub-tropical Ridge STR
The STR is expected to be near 30S this week, and that means enhanced trade winds on the north end of the traveling highs.
One high is expected to move east along 30S from date to 140W between Monday and Friday.
Another High is expected to travel east along 30 to 32S from east Australia on Tuesday to northern NZ on Thursday , fading east of the dateline on Friday UTC.
A third high is expected to depart for eastern Australia along 32/33S on Friday and reach central NZ on weekend of 19/20 October. This southward shift of the high tracks is a sign that summer is coming and is linked to a similar southward shift occurring in the jetstreams aloft.

NZ/Tasman Sea
This area continues to have a period of unsettled weather with enhanced winds thanks to passing jetstreams. Activity seems to be shifting southwards. One active front is moving across the South Island on Monday and the North Island on Tuesday morning local. A weaker front is expected mainly over the South Island on Friday.

Route Briefings
Tahiti to Tonga:
Up until Thursday UTC this route has easterly wind son the north side of a travelling High , and travel is OK. Then a trough is likely to form on the SPCZ over Cooks by Friday UTC and is expected to deepen as it travels east to Tahiti by Sat/Sun 19/20 . So better to depart Tahiti by 16 Oct UTC to avoid this trough.

Between tropics and NZ
Looking OK to depart any time this week. Winds over Fiji/Tonga may be too strong for comfort by Friday 18 Oct UTC due to the HIGH pressure system south of them by then, so nicer to depart by Thursday UTC.

Between New Caledonia and Australia
Trough crossing the Tasman on Monday and Tuesday, then OK to go. Winds over New Caledonia May become strong this weekend or early next week so try and depart before then. Next significant trough expected for Brisbane should reach there around Tue 22 October.

See my yotpak at http://lnk.ie/JO1D/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/JO1E/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/JO1F/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/JO1G/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

BOBGRAM issued 13 Oct 2013

WEATHERGRAM
YOTREPS
Issued 13 October 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.
Where to get the best weather?
If you are planning to sail from Tonga/Fiji/Vanuatu/ New Caledonia to NZ in October/ November, and looking to buddy with someone, then you may be interested in checking out the ICA's "All Points Rally" to Opua, see http://lnk.ie/JO10/e=bobmcd1.bobgram@blogger.com/http://www.islandcruising.co.nz/
Some sailors have asked me recently how good are the grib files they are downloading. Well, most of you are looking at data gleaned from the GFS model, and it's good, but not the best. A study done in 2012 shows ECMWF is usually the best. Grib data for EC is not easily available but when you have Internet you can check its latest for the next 10 days for http://lnk.ie/JO11/e=bobmcd1.bobgram@blogger.com/http://bit.ly.ecoz
Second best is the UK model, again its grib data is not easily available, but MetService pick the model of the day to feed their regional model , and it is usually EC or UK that they pick, and then it is further processed to give maps at http://lnk.ie/JO12/e=bobmcd1.bobgram@blogger.com/http://bit.ly.7daywx
So check these web sites when planning your trip (and add http://lnk.ie/JO13/e=bobmcd1.bobgram@blogger.com/http://www.swellmap.com to look at the likely swells). And if your grib data agrees with these then all is good, but if not then you need to consider multiple scenarios.

TROPICAL TOPICS
It is a busy time in the Northern Hemisphere tropics with TC PHAILIN being the largest and most intense cyclone to make landfall from Bay of Bengal into India in the last 14 years. TC OCTAVE is off the west coast of North America and re-curving towards Baja California. TC NARI is about to travel from east to west across the Philippines and head for China, and TC WIPHA seems to making a bee line for Japan.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ has been taken to the north of its range by that active squally trough which brought a S/SW change to Fiji/Tonga last Thursday night (as mentioned in my weathergram last week). During this week is should slowly drift south again, reaching Fiji and Samoa by the weekend. ECMWF model has a low forming on the SPCZ near Fiji early next week, and GFS mode, in a run dome today, has a deep low over Vanuatu early next week. Too far away to be sure at this stage, but something to keep aware about.

Sub-tropical Ridge STR
The STR is expected to be near 30S this week, and that means enhanced trade winds on the north end of the traveling highs.
One high is expected to move east along 30S from date to 140W between Monday and Friday.
Another High is expected to travel east along 30 to 32S from east Australia on Tuesday to northern NZ on Thursday , fading east of the dateline on Friday UTC.
A third high is expected to depart for eastern Australia along 32/33S on Friday and reach central NZ on weekend of 19/20 October. This southward shift of the high tracks is a sign that summer is coming and is linked to a similar southward shift occurring in the jetstreams aloft.

NZ/Tasman Sea
This area continues to have a period of unsettled weather with enhanced winds thanks to passing jetstreams. Activity seems to be shifting southwards. One active front is moving across the South Island on Monday and the North Island on Tuesday morning local. A weaker front is expected mainly over the South Island on Friday.

Route Briefings
Tahiti to Tonga:
Up until Thursday UTC this route has easterly wind son the north side of a travelling High , and travel is OK. Then a trough is likely to form on the SPCZ over Cooks by Friday UTC and is expected to deepen as it travels east to Tahiti by Sat/Sun 19/20 . So better to depart Tahiti by 16 Oct UTC to avoid this trough.

Between tropics and NZ
Looking OK to depart any time this week. Winds over Fiji/Tonga may be too strong for comfort by Friday 18 Oct UTC due to the HIGH pressure system south of them by then, so nicer to depart by Thursday UTC.

Between New Caledonia and Australia
Trough crossing the Tasman on Monday and Tuesday, then OK to go. Winds over New Caledonia May become strong this weekend or early next week so try and depart before then. Next significant trough expected for Brisbane should reach there around Tue 22 October.

See my yotpak at http://lnk.ie/JO14/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/JO15/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/JO16/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/JO17/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

06 October 2013

BOBGRAM issued 6 Oct 2013

WEATHERGRAM
YOTREPS
Issued 06 October 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

When to head out of the tropics?
Well the chances of encountering some nasty weather in the tropics is rather low at present and gradually increasing to be not worth the risk from around mid-December. Many Insurance companies do not cover weather damage in the South Pacific tropics from 1 November so that many cruising sailors leave by then—however if you wish to hang around for a few more weeks (because there are still a few cold outbreaks reaching NZ and South Australia) then, on average, there isn't much change in the risk during that time.

If you are planning to sail from Tonga/Fiji/Vanuatu/ New Caledonia to NZ in October/ November, and looking to buddy with someone, then you may be interested in checking out the ICA's "All Points Rally" to Opua, see http://www.islandcruising.co.nz/

Those who are seeking access to a weather map with isobars and fronts and convergence zones that can be down loaded via Internet can request one in FLEET code by sending an e-mail to query@saildocs.com, no subject needed, with the message "SEND nadi-fleetcode". To be able to view this map, save the number-table in it to a *.txt file and then open this with PhysPlot- You will need to FIRSTLY download and install PhysPlot from http://www.pangolin.co.nz/physplot

I shall supply more information regarding web sites for checking the weather models next week.

TROPICAL TOPICS

In East Asia TC FITOW is taking a track across northern Taiwan and into China. Following it is TC DANAS but this cyclone is expected to re-curve to the northeast and move onto Japan. In the Gulf of Mexico tropical Depression KAREN is expected to move onto southern states of USA, full of rain but wind is easing.

WEATHER ZONES

South Pacific Convergence Zone SPCZ
The SPCZ is active from Solomons to just NW of Fiji. During Fiji's Independence day holiday on Thursday 10 Oct the zone is expected to cross Fiji, and then on Friday a low is expected to deepen rapidly about and to south of Tonga, moving off to the SE. Avoid.
There is another convergence zone which is active mainly along 10S from Tuvalu to Northern Cooks. This zone is a mirror of the ITCZ that tends to form for a few weeks around the equinox and is expected to remain active this week, staying north of 11S.

Sub-tropical Ridge STR
The STR is expected to be north of its normal position this week, and that means a week of weak trade winds.
The high that is over eastern Australia on Wednesday 9 Oct is expected to move east across the Tasman Sea along around 30S and fade away just to south of New Caledonia by Fri 11 October. This is expected to be followed by another High along 30S from Sat 12 Oct and that High is likely to spread out, making mainly light winds in the tropics.

NZ/Tasman Sea

This area continues to have a period of unsettled weather with passing troughs. A Low is expected to form in the Tasman Sea on Monday and cross the North Island during Tuesday/Wednesday, deepening as it tracks to the southeast.
Another Low is expected to form on a cold front as it crosses the South Island on Friday 12 Oct. This Low should cross northern North Island on Saturday 12 Oct.

Route Briefings

Tahiti to Tonga:
Trough is expected to affect Niue on or around Tues 8 Oct and another over Tonga and Niue around Friday 11 Oct followed by a rare period of W/SW winds there on Sat 12 Oct UTC. Otherwise expect light winds this week.

Between tropics and NZ
The southerly flow in the NZ/Tasman area following the low on Tuesday makes for a period of headwinds for anyone trying to sail from New Caledonia/Vanuatu/Fiji mid to late this week. Not Good.
Those trying to get from Tonga to NZ may have a passable voyage with a departure on Wed 9 October, skirting around weather systems.

See my yotpak at http://lnk.ie/JGZ9/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/JGZA/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/JGZB/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/JGZC/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

29 September 2013

BOBGRAM issued 29 Sep 2013

WEATHERGRAM
YOTREPS
Issued 29 Sep 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.
Background influences
SOI: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin.
It maintained a value over 1 for most of June, hinting at a La Nina. Since then it has dropped to just below zero in early September and bounced back to 0.4 by 29 Sep.

TROPICAL TOPICS
TC WUTIP is heading westwards across the NW Pacific heading to make landfall in Vietnam.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is active between Solomons and Tuvalu and is expected to extend towards Niue by Wednesday UTC.
There is another convergence zone which is very active mainly along 10S from Tuvalu to Northern Cooks. This zone is a mirror of the ITCZ that tends to form for a few weeks around the equinox and is expected to remain active this week, occasionally spreading as far south to Samoa and Suwarrow.

Sub-tropical Ridge STR
The STR is still weak around the NZ longitudes and this is allowing lows to spread over the North Island. One is expected to cross this Auckland early on Monday and continue ENE, and then turn SE on Wednesday.
Over Australia and east of 180 the STR is strong along 30S as is normal for this time of the year.

Roaring 40s and New Zealand
A disturbed westerly flow, typical of spring, covers the Aussie Bight and southern NZ.

Route Briefings
Tahiti to Tonga:
Weak trough is expected to affect Niue on or around Wed/Thu UTC and another may affect Tonga from Sat to Sun 5/6 Oct. Try and time your voyage to avoid these troughs.

Between NZ and Fiji/Tonga
There is a good opportunity to travel south from Mon 30/Tue Sep/Oct as this should go nicely around the back end of a High.

See my yotpak at http://lnk.ie/J9SR/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/J9SS/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/J9ST/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/J9SU/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

22 September 2013

BOBGRAM issued 22 Sep 2013

WEATHERGRAM
YOTREPS
Issued 22 Sep 2013

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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Background influences
EQUINOX: It is logical to divide the seasons on earth use the four 'corners' of our orbit around the sun as a guide. At the equinox the earth's equatorial plane lines up with the sun's, or the sun's sub-solar point (overhead sun) crosses the earth's equator. This happens at 22:20:44 UTC, bringing spring into the southern hemisphere.
Note that day length as measured by sunrise and sunset tables is slightly MORE than 12 hours on the day of the equinox--- Because sunrise is times when the top limb of the sun clears the horizon, rather than the mid-point of the sun, same for sunset,-- and that adds 7 to 10 minutes to the day.

SOI: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin.
It maintained a value over 1 for most of June, hinting at a La Nina. Since then it has dropped to just below zero in early September and bounced back to 0.52 on 22 September.

TROPICAL TOPICS
Mexico was hit by the combo of Cyclones MANUEL in the eastern Pacific and INGRID in the Atlantic, last week, but America is free of cyclones at present. In the NW Pacific TC USAGI is about to make landfall just north of Hong Kong and the large catherine-wheel like structure of TC PABUK is posed south of Japan and expected to go then northeast skirting the east of Japan.

Looking at the anomaly map of last week's average wind we can see the monsoon has got across Philippines into NW Pacific. Another feature that shows up is the extreme anticyclone in the South Pacific - between NZ and South America intensified to over 1040 at one stage , creating squash zones of enhanced wind on its northern and southern fringes, explaining the strong winds over Tahiti.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ has broken into several small branches and these are likely to remain separate during the coming week. One is positioned from Solomons to near Tuvalu and another weak one occasionally extends west east from around Tokelau to Northern Cooks. A more intense Convergence Zone CZ over Vanuatu/Fiji is expected to go south during Monday and form a rapidly deepening Low that is likely to affect New Zealand's North Island on Tuesday and Wednesday. Avoid.
Another CZ is expected to linger over the Tahiti area this week, bring some squally showers and variable winds that come and go.

Sub-tropical Ridge STR
The STR has a weakness in the New Zealand area at present and this is expected to allow a low to deepen in the area between NZ and Fiji on Monday. This low, of tropical origin, is expected to completely disrupt the STR—and go south during Tuesday and Wednesday affecting North Island, and then peel off to the southeast.
The old STR should get pushed to the south by this low and weaken, A new STR is expected to start forming over New Caledonia by Tuesday and the slowly expand south and east into the Tasman Sea North island area by the weekend of 28/29 September.

Roaring 40s and New Zealand
A disturbed westerly flow, typical of spring, is expected to spread from the Aussie Bight across the South Tasman Sea and onto the South Island from Wednesday.

Route Briefings
Tahiti to Tonga:
There are likely to be some squally showers near Tahiti this week, but the weather pattern is looking OK on the way to Tonga.

Between NZ and Fiji/Tonga
Will need to wait for the Low to clear away, then may be OK to travel either from N to S or from S to N--- voyage will encounter some light winds from the new STR. At this stage don't have enough data for the entire voyage and so need to get another update.

See my yotpak at http://lnk.ie/J2AP/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/J2AQ/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/J2AR/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/J2AS/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

15 September 2013

BOBGRAM 15 Sep 2013

WEATHERGRAM
YOTREPS
Issued 15 Sep 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Background influences
Drought: Areas that miss out on rain for an extended time tend to have the ability to perpetuate themselves by diverting rain-bearing fronts around them. In our part of the world this has been the case for many months in northern New South Wales. However this week a rain-bearing low is expected to reach this region.

SOI: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin.
It maintained a value over 1 for most of June, hinting at a La Nina. Since then it has relaxed to around -0.07 in early September. This week is has risen to +0.11 (15 September).

GLOBAL TROPICAL TOPICS
Mexico has Cyclone MANUEL in the eastern Pacific and INGRID in the Atlantic. And there is also another Low heading west across the north Atlantic. In the NW Pacific MAN-YI is about to make landfall over Japan.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ has a main branch from Papua New Guinea to approximately Samoa. There is a smaller side branch along about 10S to north of Suwarrow. The intensity in these zones is expected to remain weak the week. The main zone is expected to drift across Samoa at times, most likely on Tuesday and Wednesday UTC. The side branch may drift south across Suwarrow on Saturday UTC.
A trough is expected to develop over Vanuatu on Sun UTC and deepen over Fiji early next week.

Sub-tropical Ridge STR
High that is tonight in the South Tasman Sea is expected to spread NE across NZ on Tuesday and Wednesday and then expand as it goes east of NZ along 35 to 33S from Thursday to Monday, intensifying the trade winds on its northern side.

Roaring 40s and New Zealand
Jetstreams have gone north to around 30S over Australia and this has bred one Low that is tonight between Lord Howe and Norfolk Islands and is expected to roll past northern NZ on Tuesday.

Another Low is now moving from Victoria to New South Wales, and is expected to deepen off Sydney on Tuesday. It has the warmth and moisture potential to bring heavy rain to New South Wales, the first decent soaking since March. This Low is then expected to track off to the south-southeast, and another low may form in Tasman Sea on Friday and cross the South Island by Sunday.

Next week the outlook is for a disturbed westerly flow to spread from Australian Bight to Tasman Sea/New Zealand.

Route Briefings
Tahiti to Tonga:
This is likely to be a week with consistent trade winds. There is an increased risk of tropical squalls near Suwarrow on Sat 21 Sep UTC (local Friday).

Between NZ and Fiji/Tonga
Take care near northern NZ as that Low flies by on Tuesday, otherwise the week offers a mix of light winds and NE/NW winds, good for travelling southwards.

See my yotpak at http://lnk.ie/IV34/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/IV35/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/IV36/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/IV37/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

08 September 2013

BOBGRAM issued 8 Sep 2013

WEATHERGRAM
YOTREPS
Issued 08 Sep 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Background influences
Jet streams
This week, and for the next few weeks Lows and Highs in the NZ area are expected to be more extreme than they have been lately, assisted by jet-streams which visit the NZ area at this time of the year.

The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin.
It maintained a value over 1 for most of June, hinting at a La Nina. Since then it has relaxed to around -0.07 (1 to 8 Sep).

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet.
This parameter has been near average so far this year, slightly on the cool side.

GLOBAL TROPICAL TOPICS
There are three possible areas of formation in the North Atlantic at present, and the low now over the Azores is likely to develop into a cyclone by Wednesday and then peel off into the mid-Atlantic.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ has increased in intensity over the Solomons, and extends as a trough which during the weekend has shifted from Fiji/Tonga to Samoa/Southern Cooks. This trough and the westerly wind that follows it is likely to skirt the Austral group on Monday UTC, and the main part of the SPCZ is expected to weaken.
There is a weak part of the SPCZ along 10S between 140 and 170W and this is expected to intensify during the coming week but should stay north of Suwarrow – this week anyway.

Sub-tropical Ridge STR
High in north Tasman Sea tonight is expected to travel eastwards along 30S past 180 on Monday and then E/SE along 30/35S for the rest of the week. This High is expected to intensify to over 1032hPa, creating a squash zone of enhanced SE winds between Tahiti and Samoa from Wed to Fri UTC (Tues to Thu local). This can bring some excitingly fast sailing but the roughened seas are likely to be uncomfortable.

Roaring 40s and New Zealand
It is to be a troughy week over NZ, with jet streams intensifying the surface winds, NW on Monday to Wednesday, and cold southerly on Friday 13th and Saturday.

Route Briefings
Tahiti to Tonga:
Squash zone over the route from local Tuesday to local Thursday with some enhanced trade winds. These conditions should ease from local Friday onwards.

Between NZ and Fiji/Tonga
Squally trough is expected to cover the area between northern NZ and 30S on Fri 13 Sep local and then a broader trough is expected on Sat 14 Sep.

See my yotpak at http://lnk.ie/INNO/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/INNP/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/INNQ/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/INNR/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

01 September 2013

BOBGRAM issued 1 Sept 2013

WEATHERGRAM
YOTREPS
Issued 01 Sep 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

1st September=start of southern Spring? Not necessarily so: the timing of the seasons is done by various conventions – there is no "official" definition.
Some people, such as climatologists who like to follow monthly means, use 1 Sep as the start of spring—very practical. Others use the four 'corners' of the earth's orbit to mark that start of the seasons, and wait for the equinox on 22 September—very logical. Others again use signs from the garden such as daffodils and can thus compare one year with another ---very interesting. I tend to be one of the logical ones.

Background influences
The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin.
It maintained a value over 1 for most of June, hinting at a La Nina. Since then it has relaxed to around -0.07 (1 Sep).

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet.
This parameter has been near average so far this year, slightly on the cool side.

GLOBAL TROPICAL TOPICS
The Baja California coast remains busy with cyclones, as KIKO reaches Hurricane force off there and travels northwards. The NW Pacific is quietening down after a few busy weeks. The Atlantic has got through half its cyclone season with NO HURRICANE yet (first such year since 2001), but there are two possible areas of formation there at present.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ currently extends from Solomons to Fiji/Tonga and has increased in intensity during the last week. It is expected to stay in much the same position during this week, but to weaken late in the week. A tropical trough is expected to move southeast along the convergence zone and cross Fiji on Tuesday and Tonga on Wednesday. This trough is expected to weaken in the tropics and continue eastwards, getting to Tahiti by Sunday, and is likely to be followed by a W/SW flow to south of 20S. There are also a few minor convergence zones near Suwarrow and Northern Cooks areas .

Sub-tropical Ridge STR
High over central NZ is expected to fade away on Monday, and High in Tasman Sea is then expected to expand so that the squash zone of enhanced SE trade wind on the north side of this High over Coral Sea and New Caledonia is expected to reach its peak by Wednesday. Also on Wednesday a High centre is expected to break free from Antarctica in the area south of NZ, this should allow the High in the Tasman Sea to extend south, and these two highs may combine to shovel a chilled southerly flow onto NZ. That's a MID WEEK POLAR OUTBREAK.
Later in the week the Tasman High should weaken and shift to the north Tasman Sea.

Roaring 40s and New Zealand
By Thursday, the trough that accompanies the mid-week polar outbreak over NZ is expected to combine with that tropical trough crossing Tonga on Wednesday so that they form a deepening complex are of low pressure east of the North Island on Thursday. The gale SW winds around this low are likely to produce high seas between NZ and Fiji/Tonga on Thursday and Friday. Avoid.
This complex area of low pressure is expected to move quickly off to the east, followed by a disturbed westerly flow over NZ on Sat/Sun 7/8 September.

Route Briefings
Tahiti to Tonga:
Avoid the squalls that are likely to accompany the trough that is expected to cross Tonga on Wednesday (afternoon local) and Southern Cooks by local Friday. This trough is also likely to be followed by a period of W or SW winds, mainly south of 20S, and these are counter progressive.

Between NZ and Fiji/Tonga
Best to wait until after the expected gale SW and high seas between NZ and the tropics on Thursday and Friday 5/6 Sept.

See my yotpak at http://lnk.ie/IFX6/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/IFX7/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/IFX8/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/IFX9/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

25 August 2013

BOBGRAM issued 25 Aug 2013

WEATHERGRAM

YOTREPS

Issued 25 Aug 2013

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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Background influences
The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin.
It maintained a value over 1 for most of June, hinting at a La Nina. Since then it has relaxed to around 0.1 (25 Aug).

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet.
This parameter has been near average so far this year, slightly on the cool side.

GLOBAL TROPICAL TOPICS

The flooding in Manila last week has been caused by a double whammy of monsoon rain and a tropical storm (TRAMI) dumping more than an average month of rain in a day. Rain in the area returned to normal last week. TC PEWA is also making its way to the NW in the NW Pacific. TC IVO is fading off the Baja Californian coast—unlikely to interfere with the final race of the Louis Vuitton in San Francisco.
Trade winds have weakened in the South Pacific between Australia and the dateline recently and the South Pacific Convergence Zone SPCZ has been stronger than normal between Papua New Guinea and Fiji/Tonga.

WEATHER ZONES

South Pacific Convergence Zone SPCZ
The SPCZ currently extends from Solomons to Fiji/Tonga and is increasing in intensity. It is expected to stay in much the same position during this week, but SE trade winds over Vanuatu and Coral Sea are expected to become strong in a squash zone as a slow-moving High forms in the Tasman Sea. There is a smaller Convergence Zone CZ along 10S around Northern cooks.

Sub-tropical Ridge STR
The new High moving into the Tasman Sea is a slow-moving one – the first we have had in several weeks, and this provides a good pattern for sailing between NZ and the Tropics.

Roaring 40s and New Zealand
Low that crossed northern NZ on Sunday is expected to move off quickly on Monday. Next trough is expected to arrive over South Island from southern ocean on Wednesday and over North Island on Thursday and then deepen into a low east of the North Island on Friday and doesn't move off to the east until Sunday. This is a classic setup for an "old man southerly" in Wellington that lasts three days. And it introduces another week if winter to NZ after a mild few weeks.

Route Briefings
Tahiti to Tonga:
As was the case last week, this week's weather pattern is looking Ok for sailing from Tahiti to Tonga or Samoa via the northern route (passing Suwarrow/Suvorov). There are not many troughs or convergence zones to worry about; however it is not expected to be entirely squall-free.
The southern route --- going via Southern Cooks /Niue—is second best this week because there is a trough that is expected to visit Southern Cooks on Tuesday/Wednesday (Monday/Tuesday local)

Between NZ and Fiji/Tonga
The slow-moving high entering the Tasman Sea offers a good pattern for travelling north with departures on Monday and Tuesday. After that the voyage is likely to be affected by that trough crossing the North Island on Thursday.

See my yotpak at http://lnk.ie/I9PE/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/I9PF/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/I9PG/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/I9PH/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

18 August 2013

BOBGRAM issued 18 Aug 2013

WEATHERGRAM
YOTREPS
Issued 18 Aug 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Background influences.
The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin.
It maintained a value over 1 for most of June, hinting at a La Nina. Since then it has relaxed to around 0.5 (18 Aug).

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet. This parameter has been near average so far this year, slightly on the cool side.

GLOBAL TROPICAL TOPICS
Tropical Depression ERIN is weakening in the North Atlantic and it becomes subtropical. TC TRAMI is expected to take a path westwards into China to north of Taiwan this week, after TC UTOR killed at least four people and displaced more than 320,000 in Southern China las6t week. TC PEWA is also making its way to the NW in the NW Pacific. The Cyclone season is getting busy.
Monsoon seems to be weakening. In fact rain around the planet seems to have been below par last week, with the wettest zone in the South Pacific being from Samoa to Suwarrow.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ currently extends from Solomons to Tuvalu/Samoa to west of Tahiti at present and is expected to divide into two branches during the week, with one near 10S and the other between Fiji and southern Cooks. A small but intense and squally LOW may form on the SPCZ and visit northern Vanuatu on Wednesday and then move SE. Avoid.

Sub-tropical Ridge STR
There is part of the STR between NZ and Fiji/New Caledonia with a weak extension further east. There is a strong and slow-moving High over Australia and this is expected to finally start moving east into the Tasman Sera after Sat 24 Aug-not before.
The High that is east of NZ by mid-week is expected to move northeast from out of the southern ocean, and so is a cold high. There should be a squash zone of strong winds on its northern side. The SAM (Southern Annular Mode) index became very negative last week, indicating that any southerly outbreak – such as that on the eastern side of this high- is polar-chilled.
A low crossed northern NZ on Saturday and is expected to continue to move east along 35 to 30S this week, between the two ridges.

Roaring 40s and New Zealand
A disturbed and sometimes showery northerly/westerly flow is expected over NZ this week.

Route Briefings
Tahiti to Tonga:
This week's weather pattern is looking Ok for sailing from Tahiti to Tonga or Samoa via the northern route (passing Suwarrow/Suvorov). There are not many troughs or convergence zones to worry about; however it is not expected to be entirely squall-free.
The southern route --- going via Southern Cooks /Niue—is second best this week because there are several troughs expected to make their way eastwards between 18 and 25S associated with the low that is expected to travel east along 35 to 30S.

Between NZ and Fiji/Tonga
The disturbed northerly/westerly flow this week is not a good weather pattern for going north or south. If a slow-moving high does enter the Tasman Sea this weekend then there may be an OK pattern for sailing north starting early next week.

See my yotpak at http://lnk.ie/I4K6/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/I4K7/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/I4K8/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/I4K9/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

11 August 2013

BOBGRAM issued 11 August 2013

WEATHERGRAM
YOTREPS
Issued 11 Aug 2013

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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Background influences
The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin.
It maintained a value over 1 for most of June, hinting at a La Nina. Since then it has relaxed to around 0.7.

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet.
This parameter has been near average so far this year, slightly on the cool side.

GLOBAL TROPICAL TOPICS
The Atlantic hurricane season is on track to be above normal from mid Aug to late October.
http://lnk.ie/HYEL/e=bobmcd1.bobgram@blogger.com/http://www.noaanews.noaa.gov/stories2013/20130808_atlantichurricaneupdate.html

At present there are two TC's. One, called UTOR, is tracking across northern part of Philippines and is expected to make landfalls to SW of Hog Kong on Wednesday. T'other, called Henriette, is traveling from east to west along path south of Hawaii. The winds of the SW Monsoon over India are starting to ease, compared with last week.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is expected to spend the first half of this week along roughly 10 to 12S. After Wednesday 14th UTC it is expected to drift southwards across Samoa, then it should cross Suwarrow on Friday and Southern Cooks on Saturday forming a Low near 23S 160W by Mon 19th UTC that is then expected to deepen and move off to the SE. This is likely to be a squally trough, one to avoid if possible.

Sub-tropical Ridge STR
The STR starts the week off strongly at its winter latitude of round 25/30S.
The High cell over central Australia on Wednesday is expected to cross the northern Tasman Sea on Friday and then the North Island on Saturday and move off to the east from Sunday.

Roaring 40s and New Zealand
A disturbed and boisterous westerly flow covers the mid-Tasman Sea and North island until Wednesday, albeit with the brief calm of a passing ridge on late Monday UTC. Thursday may be an OK day for departing to the north, but the NW/SW winds of the next trough are then likely to be encountered by Tuesday/Wednesday 20/21 Aug.

Route Briefings
Tahiti to Tonga:
Avoid that trough that is expected to cross Samoa on Wed/Thursday UTC and Suwarrow on Friday, Southern cooks from Saturday 17th UTC. If you depart early in the week you should be able to reach Suwarrow or Palmerston before the trough does, and wait out the passing trough there.
I am unsure how to compare the sheltering conditions of Suwarrow and Palmerston… I think Suwarrow will have a briefer impact than Palmerston from this trough, so maybe if you do intend to start this voyage this week, then leave early and go to Suwarrow and no further.

Between NZ and Fiji/Tonga
Travelling south arrange to arrive between Sat 17 and Tue 20 Aug.
Going north, there may be an OK departure on Thursday/Friday 15/16 Aug, but after that these voyages are likely to encounter Northerly winds by Tuesday 27th.

See my yotpak at http://lnk.ie/HYEM/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram text only and translator is http://lnk.ie/HYEN/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Weathergram with graphics is http://lnk.ie/HYEO/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Website http://lnk.ie/HYEP/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

04 August 2013

Bobgram issued 4 Aug 2013

WEATHERGRAM
YOTREPS
Issued 04 Aug 2013
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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Background influences
The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin. It maintained a value over 1 for most of June, hinting at a La Nina. During early July it dropped to around 0.7 from kid to late July and rose to 0.9 in early August.

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet.
So far this year NINO3.4 has been on the cool side, but rather weak.

GLOBAL TROPICAL TOPICS
There has been some unusual tropical action over Hawaii, FLOSSIE made landfall, and now GIL is weakening as it takes a track south of the Islands followed by another tropical depression.
Over Asia, SW/W Monsoon wind and rain have relaxed a little over Indonesia There has been some active convection over Philippines. No TC as yet, however, the risk remains moderate to high in this region this week.
In the past week there was a squash zone over the Marquesas area but trade winds were below par over remainder of South Pacific.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ rebuilt last week from Solomons to Suwarrow and there was a convergence zone around the centre of a low that formed near 30S to South of Southern Cooks.
This week the SPCZ is expected to intensify and move south, reaching from Samoa to Papeete by Tuesday then splitting and relaxing over French Polynesia but shifting south in-between Vanuatu and Fiji on Thursday and forming a LOW between Fiji and NZ on Friday that then rapidly moves SE and deepens to east of NZ by Saturday 10 August .

Sub-tropical Ridge STR
High cell in the STR to east of NZ is currently 1035+ near 45S and expected to weaken back to below 1030 by Wednesday. To west of 180 STR is reforming along 30S and remains weak, so that there is no squash zone in the trade winds to the north.

Roaring 40s and New Zealand
W/NW flow over NZ on Monday and Tuesday, and a trough crossing NZ on Wed to Friday, then a Low is expected to deepen to NE of NZ on weekend Sat/Sun 10/11 Aug UTC with a weak ridge over NZ.

Route Briefings
Tahiti to Tonga:
Wait until the trough clears Tahiti and the winds revert to be from S/SE either on Tuesday or Wednesday. The next trough is expected to cross Aitutaki on Tues 13/14 Aug, so it may be better to go via Suwarrow.

Between NZ and Fiji/Tonga
Keep an eye on that Low from Fid 9 to Sun 11 Aug.

See my yotpak at http://lnk.ie/HS6A/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/HS6B/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/HS6C/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/HS6D/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

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