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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
Website is at metbob.com Feedback to bob@metbob.com To unsubscribe send
an email to bob@metbob.com saying unsubscribe or, if you have web access,
go to %%UNSUBSCRIBE%%

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
Website is at metbob.com Feedback to bob@metbob.com
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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

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