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

31 August 2014

BobBlog 31 Aug 2014

WEATHERGRAM
YOTREPS
Issued 31 August 2014
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

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 has been negative since July and has been hovering around -5 (Australian
units) for the past month - enough to be called a weak El Nino. --

TROPICAL TOPICS
After a busy period, activity has relaxed for the moment in the tropics and
there are no Tropical Cyclones around the planet at present.
The weekly rain maps for the past fortnight show a continuing burst of rain
around India. Activity between Mexico and Hawaii has eased, and there has
been a well-defined band of rain across the SW Pacific. It also continues to
be wet in the northern Tasman Sea.

WEATHER ZONES
SPCZ= South Pacific Convergence Zone
The SPCZ is now well established expected along 10S from 165E to 165W and is
likely to drift southwards towards Samoa later this week. A weak branch of
the SPCZ is drifting eastwards across French Polynesia this week and is
expected to help in the formation of a low near 30S 135W from Wednesday 3
Sep UTC.

Departing westwards from Tahiti:
The convergence zone that has been lingering over French Polynesia over
recent days should travel southeast off the group allowing trade winds to
move onto the area by local Tuesday, good enough for departure.
The SPCZ may travel slowly south towards Samoa by late this week. If this
track continues into next week then it may reach northern Tonga after 7
Sept, so keep a watch out for that A squash zone of strong SE winds is
likely to form between Tahiti and Samoa on Thur/Fri/Sat UTC and then drift
to the southeast- this squash zone is associated with the northeastwards
travel of a large high along
40 to 30S in the southern ocean. Uncomfortable.

STR= Sub-tropical Ridge
The STR is well south of its normal position this week. The intense high
referred to in my blog last week did indeed linger over southern NZ at over
1034hPa, with lots of low cloud and drizzle under its inversion affecting
various coastal parts of NZ (a dirty high). It is now east of NZ and
travelling eastwards along 45S. This high is well supported aloft and slow
to move, a good example of what is sometimes called an omega
block.

Between NZ to the tropics
Not a good week for travelling south to NZ.
There is a squash zone of enhanced NE to easterly winds between the high
east of NZ and a Low tonight over northern NZ.
On Monday, Low is expected to move slowly across Northland (at 1008 it isn't
very intense but because its rain bands are slow-moving they have a high
accumulative affect).
On Tuesday, that Low should finally move off to the east allowing a day of
SW winds that may be good enough for setting sailing off to the north (but
may encounter a period of strong winds on Thursday night near 30S).
However another Low is expected to form in western Tasman Sea on Tuesday,
rapidly deepening to 990hPa on Wed/Thu and then traveling onto North Island
on Fri/Sat. Its associated warm front is likely to cross North Island on
Thursday and be preceded by strong northerly winds and followed by strong
squally westerly winds near NZ. Avoid.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom
right to subscribe.
My website is at metbob.com  Feedback to bob@metbob.com To unsubscribe,
send a reply email saying unsubscribe.

24 August 2014

BobBlog 24 Aug 2014

WEATHERGRAM
YOTREPS
Issued 24 August 2014
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

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 has been negative since July and has been hovering around -5 (Australian
units) for the past month - enough to be called a weak El Nino.

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.
Comparing the current evolution of Nino 3.4 with recent episodes shows us
that there is normally a drop around this stage of the episode and that
there is still plenty of time for this episode to grow stronger by early
2015.

TROPICAL TOPICS
It is all happening in the NE Pacific with Hurricane KARINA and Tropical
storm LOWELL and MARIE travelling NE/NW not expected to make landfall.
For the latest official data on these features see http://www.nhc.noaa.
gov/?epac
The weekly rain maps for the past fortnight show a burst of rain around
India and heaps of convection between Hawaii and Mexico. Also the South
Pacific Convergence zone is becoming less defined.

WEATHER ZONES
SPCZ= South Pacific Convergence Zone
The SPCZ is expected to intensify this week and stay with one branch between
Solomons and northern Vanuatu, and another branch between Tuvalu and Tokelau
occasionally affecting Samoa, and a third branch mostly lingering over
Southern Cooks but expected to drift onto French Polynesia by end of this
week.

STR= Sub-tropical Ridge
The STR has come south and intensifies since last week, The INTENSE High
(more than 1034 at centre) over South Tasman Sea and southern NZ today is
slow moving and should finally weaken and move off to the NE of South Island
from Thursday. This is a winter anticyclone so there is plenty of stratus
cloud under its inversionwhat some people call anticyclonic gloom , so it
maynt bring the 7 sunny days that some may have promised.
A squash zone of strong trade winds are found in the tropics on the north
side of this high These strong SE winds are already affecting Fiji/parts of
Tonga, and should continue there until around Thursday. The squash zone
should spread east to Samoa by local Monday, lasting there to local
Thursday, to Niue for local Wednesday to Friday, and Southern cooks for
local Friday and Saturday.

Departing westwards from Tahiti:
There are three challenges/complications: 1) the SW winds that are likely
around Southern Cooks until local Monday; 2) The convergence zone that is
expected to develop and linger over Southern cooks by local Tuesday and
linger there a few days and then travel east to French Polynesia by local
Saturday; and 3) the squash zone that is travelling east later this week.
It may be possible to make short trips and dodge around these factors.
Anyway none of these challenges are likely to be too intense this week 
they may make things uncomfortable at times but should still allow sailing.

Between NZ to the tropics
A subtropical Low is now deepening off Brisbane and expected to remain
slow-moving there for a few days, finally weakening and travelling east
along 30S across to north of North Island by the weekend.
Associated front should spread strong to gale easterly wind and heavy rain
onto northern North Island from the north during Wednesday to Friday.
Avoid.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom
right to subscribe.
My website is at metbob.com  Feedback to bob@metbob.com To unsubscribe,
send a reply email saying unsubscribe.

17 August 2014

BobBlog 17 August

WEATHERGRAM
YOTREPS
Issued 17 August 2014
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

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 has been negative since July and has been hovering around -5 (Australian
units) for the past month - enough to be called a weak El Nino.

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 warmer than normal since March, but in the past week
has returned to normal. This mean that there WAS an oceanic signal towards
El Nino over past few months, and now its gone.
There WAS a lot of extra heat stored in the sea over the past few months.
At present this is presenting itself mainly as zones of warmer than normal
sea in the North Pacific  right in the middle of the North Pacific cyclone
season.

GLOBAL TROPICAL TOPICS
Cyclone KARINA is located between Mexico and Hawaii along with two other
tropical depressions. These are expected to travel west then north and
weaken, but another cyclone is expected to form in the area later this week.
Busy.
There is also a tropical depression in the North Atlantic. Its future is
uncertain at this stage but it may head towards Puerto Rico later this week.

Taken as a whole, the area between Hawaii and Mexico has shown strong
convection in the past week. Also convection has dropped over the Asian area
in the wake of last weeks cyclone HALONG in early August.
The weekly rain maps for the past fortnight show an enhancement in
convection between Hawaii and Mexico.

WEATHER ZONES
SPCZ= South Pacific Convergence Zone
The SPCZ is in much the same position as last week, and starting to
intensify between Papua New Guinea and Vanuatu.
The north end of a passing trough is expected to travel east across central
and southern parts of French Polynesia on Wednesday UTC/local Tuesday.

STR= Sub-tropical Ridge
High over 1020 (not very intense) over North Island on Monday is expected to
travel east along 30/35S this week  no squash zone on its northern side.
High over 1025 (moderate intensity) over Tasmania on Wednesday is expected
to intensify and spread along 45S and onto southern NZ this weekend 23/24
August.

Departing westwards from Tahiti:
It may be a good idea to wait for that convergence zone to pass by on local
Tuesday. Also note that the next trough is likely to reach Niue area by
local Thursday, followed by W/SW winds for a few days

Between NZ to the tropics
An intense front is expected to cross North Island on local Tuesday night,
followed by NW winds on Wednesday, and a trough on Wednesday night. On
Thursday this trough is expected to deepen into a low east of the North
Island bringing a southerly gale to central NZ, probably not as cold/snowy
as last weeks was. It should be OK to depart from Northland to tropics on
Thursday and Friday, but not before.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom
right to subscribe.
My website is at metbob.com  Feedback to bob@metbob.com To unsubscribe,
send a reply email saying unsubscribe.

10 August 2014

BobBlog issued 10 August 2014

WEATHERGRAM
YOTREPS
Issued 10 August 2014
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.

There is a closer gap between perigee (1743UTC 10 Aug) and full moon
(1809UTC 10 Aug) this month than there was last month or will be next month,
and so tonight is the biggest full moon of the year, followed for the next
three days by KING TIDES. Take care out there.

TROPICAL TOPICS
More action in the past week with 5 cyclones across the Pacific and Atlantic
basin at once.
ISELLE hit Hawaii hard, and it is looking as if JULIO, following it, has
now diverted to the north.
And at present TC HALONG is crossing Japan

WEATHER ZONES
SPCZ= South Pacific Convergence Zone
Continues to be rather weak, but a branch is expected to intensify over
Tonga on Thursday/Niue on Friday/ and Southern Cooks on Friday UTC.

STR= Sub-tropical Ridge
An intense HIGH is expected to build to over 1040 in the Aussie Bight by
Wednesday. This intensifies the winds over Australia. This High is
expected to travel NE across the Tasman Sea and weaken to below 1030 by the
time it reaches NZ around early next week, but should bring a squash zone of
enhanced trade winds to Coral Sea by Thursday spreading to Fiji by Friday.

Departing westwards from Tahiti:
OK to depart and travel west to Suwarrow, but a departure to more southern
places such as Niue are likely to encounter a convergence zone late in the
week.

Departing from NZ to the tropics
An intense front is crossing NZ on Monday and Tuesday followed by a strong
cold S/SW flow on Wednesday to Friday. This should relax on Saturday and
weaken on Sunday/Monday as that HIGH arrives over northern NZ.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom
right to subscribe.
My website is at metbob.com  Feedback to bob@metbob.com To unsubscribe,
send a reply email saying unsubscribe.

03 August 2014

BobBlog issued 3 Aug 2014

WEATHERGRAM
YOTREPS
Issued 3 August 2014
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.

Negative storm surge
A few weeks ago I shared on my blog that I was having problems explaining
the consistent negative storm surge at Green Island. I have been since
informed by NIWA that the gauge was damaged and the new pipe ended up being
shorter than the previous one, so was reading lower than before.
An offset has been applied and readings are OK now.

TROPICAL TOPICS
More action this week
Tropical Storm BERTHA in North Atlantic
ISELLE is expected to weaken as it approaches Hawaii.
HALONG is approaching southern Japan.
And NAKRI is visiting Korea.
The weekly rain maps for the past fortnight show a northward shift in the
tropical convergence zone over the NW Pacific. Not much change in the South
Pacific.

WEATHER ZONES
SPCZ= South Pacific Convergence Zone
The SPCZ has been steady in position for a week or so, and part of it may
spread south into Coral Sea or onto Fiji by the end of this week. A Low is
expected to form near 25S 140W by Monday (Sunday local) and this feature
should go SE this week.

STR= Sub-tropical Ridge
There is a High moving east well to the east of NZ along 30 to 35S this week
on Monday. It has a squash zone of enhanced trade winds on its northern
side around 10 to 15S which has recently been bothering Fiji and Tonga and
is expected to bother Samoa on Monday and Southern Cooks on Tuesday (UTC).
The next HIGH is expected to depart the Aussie bight on Wednesday and travel
east along 30/35S reaching northern NZ on Sunday 10.

Departing westwards from Tahiti:
OK to depart and travel west, but be mindful that there are some strong SE
winds around until Tuesday UTC.

Departing from NZ to the tropics
A low is expected to cross central North Island on Monday, bringing a
squally change to SW winds to Northland in the afternoon: that could be a
boost for departures going north- or maybe some might prefer the quieter
winds on Tuesday. A Monday departure should get a better go (than a Tuesday
departure) at crossing the light wind zone of the
subtropical ridge near 30S. After Friday winds are likely to get too
light for a good departure.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom
right to subscribe.
My website is at metbob.com  Feedback to bob@metbob.com To unsubscribe,
send a reply email saying unsubscribe.

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