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

27 September 2015

Bobgram issued 27 Nov 2015

WEATHERGRAM

YOTREPS

Issued 27 September 2015

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.

 

Note that NZ has switched to Daylight Time today .

 

There is a full tide in the middle of the  night when we have the  last quarter moon.  Well, the one after  the equinox (and that’s around 5 Oct this year) normally triggers a spawning of the Palolo coral warm. They drop off their worm-tails or pods; jade (female) or brown (male); and these mix together in the swirling tide, with each having a light sensitive spot that directs it towards the moon as it sinks in the west (or a flashlight). At dawn the pods dissolve, allowing eggs and sperm to get together and form the new generation. The rising is only on the turn of that one tide and only takes place for a few hours. Actual timing varies each year, and is usually in October, but may be followed by a minor event a month later.

A bowl of Palolo may be seen at http://www.ird.

fr/recherche/santo2006/blog/index_bestanden/13oct/13oct_3_gen.htm

This is worm sex-Pacific style. The pods can accumulate in the sea in massive amounts. Ask the locals about this and if you time it right you may be about to collect some of this rare delicacy, or photo it. They might look yucky, but taste really nice on toast, something like caviar, so I’m told.

 

El Nino and the SOI

AN El Nino occurs when the Earth’s ocean/atmosphere system stores incoming energy from the sun as heat in the sea. Its atmospheric aspect can be measured by a parameter related to the barometric pressure difference between Tahiti and Darwin, a parameter called the Southern oscillation index SOI. This went into El Nino territory briefly in June and more definitely in August and has been very strongly negative throughout September.

This index usually encourages the fronts and disturbed W/SW winds of the southern ocean to visit the NZ/Tasman Sea area. Yet in the past week we have had the opposite weather pattern with a cut-off low feeding easterly winds onto northern NZ—Heavy rain in places which desperately need it.

Weather is truly a mix of pattern and chaos.

 

TROPICAL TOPICS

There are three tropical cyclones and a tropical low at present In the Atlantic is the remains of TC IDA Near the Mexican coast is TC MARTY Near Hawaii is TC NIALA And approaching Taiwan is TC DUJUAN The weekly rain maps, as seen athttp://trmm.gsfc.nasa.

gov/trmm_rain/Events/big_global_accumlation.gif, over the past two weeks show that maximum rainfall in the South Pacific has shifted so that it now is situated between NW of Fiji and the equatorial dateline.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.  There is a lot of activity between Eq. 180 and the NW of Fiji at present.

This is expected to spread eastwards (westerly winds aloft) and stretch across Tuvalu and Tokelau towards Northern cooks and maybe the Tuamotu Islands. A new branch of the SPCZ is likely to form in the Coral Sea later in the week.

 

STR= Sub-tropical Ridge

High us building eats of NZ on Monday and Tuesday UTC and expected to travel east along 35S from Wednesday to Friday with a squash zone of strong trade winds over the Fiji /Tonga/Samoa area in parts on Thu 1  to at 03 Oct.

New HIGH is expected to travel from interior of Australia to Tasman Sea on Fri 2 Oct then travel slowly east along 30S until 4 Oct and then along 40S from Mon 4 to Tues 06 October. On the northern side of this HIGH there is likely to be a squash zone of stronger trade winds over the Coral Sea from 30 Sep UTC stretching onto New Caledonia by Friday 2 Oct and Fiji by Sun 4 Oct maybe lasting at least until 10 October.

 

Travelling Tahiti to Tonga

It is a better looking pattern than last week:

There is a Low well off to the south of Tahiti at present. Its squalls are well off and of no concern but it has “stolen” the winds around Society winds so that departure in net few days are in light winds.

Southerly winds are forecast to return by Tues UTC/Monday local and Se winds from Wed UTC /Tues local. Squash one of strong SE winds and 3

metre+ swells is expected to be strongest over Tahiti area around Sat 3

Oct/Friday local. Remainder of voyage westwards to Tonga basically has SE winds 20 gust 30 knots this week.

 

NZ

NE (onshore) flow onto Northland on Monday to Wednesday as HIGH to east of country builds and finally moves off to the east, Cold front on Thursday is likely to be followed by strong SW flow on Friday 2/Saturday 3 Oct as the front may turn into a Low off the E of North Island.

An intense Low 980 hPa is likely to travel east across South Tasman and South Island along 48S on Sun 4 / Mon 5 Oct, followed by a strong S/SE flow spreading over NZ on Mon 5 Oct and Fiji /Tonga on Wed 7/Thu 8 Oct.

 

Between Tropics and NZ:

There are no comfortable voyages from Tonga or Fiji this week, unless they can reach Northland by Thursday 1 Oct, before the SW winds of 2 Oct.

Departures from New Caledonia or Australia to NZ may be able to cope with these SW winds, and may find the swell bumpy but OK.

>>>>>> 

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com. Tell anyone you like that to subscribe they should email me.

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.

To unsubscribe send a reply email saying LEAVE.

 

 

20 September 2015

Bob Blof 20Sep 2015

WEATHERGRAM

YOTREPS

Issued 20 September 2015

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.

 

Welcome (on Wednesday) to the vernal equinox (in Southern Hemisphere).

Our Sun, viewed from earth, crosses our equator at 08:21 UTC (8:21pm NZST).

The next full moon (fullest at 2:51UTC on Monday 28th Sep) occurs within a few hours of this month’s lunar perigee (closest at 1:46UTC). This just happens to be the closest that the moon gets to earth for the year at 357,

126 km. Yes, this means the full moon this moon will appear to be bigger than normal. It is a perigean moon, some call it a “super moon”. The moon is also going to cross the ecliptic and thus move into earth’s shadow (lunar eclipse). Mid–eclipse is 2:47UTC. This eclipse is best viewed from the America’s, and they are preparing for a “blood moon”, not visible from South Pacific. The reason I’m relating all this background info is that the corresponding tides are called “king tides” or “perigean tides”

and will have higher and lower extremes than normal, reaching their peak around Wednesday 30 Sep. Take adequate precautions.

 

Astronomical data on the 28Sepeclipse is available at http://eclipse.gsfc.nasa.gov/LEdecade/LEdecade2011.html

 

NIWA in NZ have now published their September edition of the seasonal Outlook for the South Pacific at http://www.niwa.co.nz/island-climate-

update-180-september-2015/tropical-rainfall-and-sst-outlook-september-to-

november-2015

 

El Nino is expected to intensify and that is likely to weaken the trade winds and pull the South Pacific Convergence zone north and east of its normal position. There are likely to be bursts of equatorial westerly winds around PNG and Solomon Islands.

Drier than normal conditions are likely around New Zealand and in the New Caledonia/Fiji/Tonga area Note that this is a seasonal forecast, and, as we shall see later in this blog , this week bucks this trend.

Also, cooler than normal sea surface temperatures around New Zealand and in the New Caledonia/Fiji/Tonga area may reduce the likelihood of severe tropical cyclones in these areas.

 

AN El Nino occurs when the Earth’s ocean/atmosphere system stores incoming energy from the sun as heat in the sea. Temperatures in the target zone (measured by the NINO3.4 index) in the eastern equatorial Pacific have now intensified to 2 full degrees above normal as seen at http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?

c=nino34&p=monthly .

They are still intensifying and are expected to peak around the turn of the year.

The graph shows that they still have a while to go to rival the 1997/98 El Nino.

 

TROPICAL TOPICS

There are more tropical features around than last week including two tropical cyclones.

As seen at http://tropic.ssec.wisc.edu/

In the Atlantic we have TC IDA

And off to NE of Japan we have TC KROVANH The weekly rain maps over the past two weeks show that rainfall in the South Pacific is intensifying and extending to the southeast.

Weekly rain signatures for past two weeks, as seen at http://trmm.gsfc.

nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

There is a lot of activity between Eq. and 5S from 160E to 180 at present and this moisture is expected to feed west then S then SE along SPCZ that extends from eastern Solomon Islands to Fiji. Another branch of the SPCZ is expected to linger around tokelay and Northern Cooks.

The 10 day rain accumulations at windyty.com confirms these ideas

 

STR= Sub-tropical Ridge

This is very weak over the Pacific at present.

The High over Australian Bight on Wednesday is expected to spread eat to South Island for Fri/ Sat 25/26 Sep. The reason it is being diverted so far south is because of the cut-off lows in the Tasman Sea. We meteorologists have a name for this pattern – “low index” meaning that one of the zonal parameters we use to measure the weather (Z1) is taking negative values --- the isobars are higher in reading over the South Island rather than the North Island. These low index patterns occur occasionally, even at this time of the year (the equinox) BUT they are the antithesis of El Nino, so I suspect that next High will take a different route and go NE across the Tasman Sea and return us to a “high index” pattern early in October. Meanwhile the eastern and Northern North Island will welcome the rain this week, for the season forecast is for dry, dry, dry.

 

Travelling Tahiti to Tonga

The rain accumulation map shows that it should be dry from Tahiti to Southern Cooks. However, Trough over Tonga on Monday UTC and Niue on Tuesday UTC. After that the trough is expected to weaken and there may be a ridge of light winds along the route—OK for motoring, but not so good for sailing.

The outlook shows a better looking pattern next week.

 

NZ

The cut-off Low located east of Auckland at present should dominate

conditions over the North Island until Wednesday local (some call this

the “olde man southerly” pattern). Then a brief ridge for the North

Island on Thursday.

Another Low is expected to form and cut-off just east of New South Wales

on Tuesday. Its deepening should bring a gale to Sydney/Coffs by

Wednesday. Then this low should travel east along 30S affecting northern

NZ from Friday to Sunday 27 Sep.

 

Between Tropics and NZ:

There are a lot of southerly winds on the western side of these Cut-off

lows until Friday. Things may be OK for a departure after Saturday 26Sep,

not before.

>>>>>> 

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage

forecasts– Feedback to bob@metbob.com. Tell anyone you like that to

subscribe they should email me.

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at

bottom right to subscribe.

To send a reply email saying LEAVE.

17 September 2015

Tsunami currents today

Last night’s Tsunami arrived at Chatham Island around midnight NZ time and has been affecting east facing NZ harbours with swirling currents.

 

At Tutukaka, north of Whangarei in Northland locals are commenting the onset wave was around half to 1 metre high, and currents have been coming for ten minutes then going for ten minutes , and different parts of the harbour having different currents—something like a 20 minute tidal cycle.

A good web site to see the impact is http://www.geonet.org.nz/tsunami/ which shows the waves compared with the normal tides, and also has a “de- tided” diagram 

 

Today’s image shows that the Tsunami currents had their largest wave heights at onset, and are still going.  There have been several aftershocks in Chile ,  so these currents may be expected to linger all day today.

Bob McDavitt

 

Tsunami Tonight

The 8.3 quake over Chile at  around 16 2300UTC  (11am  Thursday NZ time) 

and its aftershocks   has generated Tsunami waves which are travelling

westwards across the South Pacific tonight.

 

For the latest NZ advice on these waves see http://www.civildefence.govt.nz/

 

Basically sea level rises and falls in the order of .2 to 1 metre are likely along east facing coast lines overnight tonight, along with swirling currents in harbours with a period of around 20 minutes.

 

A graphic showing  the expected timing  of the first of the  Tsunami waves is at

http://www.stuff.co.nz/national/72147349/tsunami-warning-for-coastal-parts-of-new-zealand-after-big-chile-quake

The 12hr line corresponds to 11pm  New Zealand time The same scoop article relays a graphic from NOAA of the expected energy propagation.

 

Waves are expected to lose grunt west of 160W, and fade away west of 180,  but there are likely to be ribbons of extra energy all the way to the NZ and Samoa/Tonga/Fiji coasts, especially around Chatham Islands.

 

A good site to monitor these waves are the sea=level gauges at NIWA

e.g.  http://www.niwa.co.nz/our-science/coasts/tools-and-resources/sea-levels/marsden-point

or the GNS tidal network at http://www.geonet.org.nz/tsunami/

 

Bob McDavitt

 

 

 

13 September 2015

BOBblog 13 sep 2015

WEATHERGRAM

YOTREPS

Issued 13 September 2015

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.

 

Where are we with El Nino?

SOI (the atmosphere)

The SOI (Southern Oscillation Index) measures the (normalized) air pressure difference between Tahiti and Darwin.

This parameter has been in El Nino territory since July. El Nino has recently been encouraging disturbed SW wind condition in the Tasman Sea/NZ area, but, as we shall see, the opposite is about to happen for a week or so, as some sort of atmospheric fling.

The SOI can be seen at http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekly

 

TROPICAL TOPICS

There are some tropical lows around as seen at http://tropic.ssec.wisc.edu/) but no tropical cyclones at this time:

 

WEATHER ZONES

 

SPCZ=South Pacific Convergence zone.

This extends from Solomons area to the Fiji/Samoa/Tonga area by mid-week.

 

STR= Sub-tropical Ridge

The HIGH that is in the Tasman Sea on Monday 14 UTC is expected to travel east along 30 to 35S, crossing northern NZ on Tuesday and then off to east of NZ for the remainder of the week.

It is an intense high and is expected to grow to over 1028hPa by Thursday.  There is expected to be a squash zone of strong winds on it northern side over the Tonga area from late Wednesday and affecting the in the Niue/Southern Cooks areas on Thu/Fri UTC Avoid.

Next HIGH is expected to cross Tasmania on Friday and then southern NZ on Saturday and linger over Chatham Islands area for the next week, with a squash zone of strong E /NE winds over northern NZ.  This is the opposite of the El Nino pattern so is just an atmospheric fling. It is a good pattern for sailing from New Caledonia/Vanuatu to Australia.

 

Travelling Tahiti to Tonga

The north end of a passing front is expected to bring a period of changing winds and maybe a few showers to Society Islands on local Sunday (Monday UTC) followed by good SE winds for a departure to the west on local Monday/Tuesday.  However a departure on local Monday is likely to encounter period of strong SE winds on local wed/Thu. A departure on local Tuesday/Wednesday should only have a brief encounter with strong SE winds on Thursday. And a Thursday departure should miss the strong SE winds.

 

NZ

TROUGH moving across Tasmania on Monday UTC is expected to travel across NZ on Wednesday/Thursday/Friday.  The north end of this trough is expected to bring a change to light southerlies and showery weather to New Caledonia/Vanuatu on Friday ,  and this is then expected to deepen into a LOW near 25S 175E by Saturday UTC, with strong to gale NE winds in a zone between NZ and Tonga.  This Low is forecast to travel SE and bring some sort of easterly gale to northern NZ by Sunday UTC, possibility lingering for a few days.

 

Between Tonga and NZ:

Southern Tonga is expected to have strong ESE winds in a squash zone from Wednesday and between Tonga and NZ there is likely to be strong to gale NE winds from Friday to Sunday, with strong easterly winds persisting near Northland into next week.  SO not a good week to sail from Tonga to NZ.  If you are going the other way then go north to west of around 175E, so that you can go clockwise around the developing Low.

>>>>>> 

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com. Tell anyone you like that to subscribe they should email me.

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.

To unsubscribe send a reply email saying LEAVE.

06 September 2015

Bob Blog 6 Sep 2015

WEATHERGRAM

YOTREPS

Issued 6 September 2015

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.

 

Weather anomalies in August as seen at http://www.esrl.noaa.gov/psd/map/images/fnl/slp_30.fnl.anim.html

and at http://www.esrl.noaa.gov/psd/map/images/fnl/slp_30a.fnl.anim.html show there was a  very strong sub-tropical ridge over the Australian bight and to south and east of NZ, with increasing intensity in the troughy conditions across the tropical North pacific (around 5 cyclones

in 4 weeks) and also over Tahiti to Cape Horn.   Typical El Nino conditions are solidly in place. 

The troughy conditions that were over Solomon Islands have shifted east towards Tuvalu.  There are slight above normal pressures over most of Asia showing a stuttering Monsoon, but Myanmar/Burma stands out as lower than normal pressures and has had floods and landslides last month killing over 100 and affecting over one million people.

 

Outgoing Longwave radiation OLR is a parameter that can easily be measured by satellites.  It is inversely proportional to cloud cover (OLR is highest over clear skies) So blue readings in the map correspond to bubbly clouds and yellow /red readings are mellow /quiet/cloud free areas.

From http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjoupdate.pdf we can see that maps of last month’s OLR readings show that convection has been strong in the equatorial and tropical north pacific.

There was a period in early August of strong convection over Solomon Islands, and then rather quiet convection in the South pacific during mid and late August.

 

TROPICAL TOPICS

There are five tropical cyclones at present FRED is located in mid North Atlantic and weakening:

GRACE is to the SE of FRED and heading for Dominica in the Caribbean Islands.

KEVIN is off the Mexican west  coast

JIMENA is to the north of Hawaii:

And KILO is to the NW of Hawaii, heading for the Japan area The weekly rain maps over the past two weeks as seen at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

show a weakening in the rainfall in the South pacific during the past week.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

Nothing organised at present.  Main band extends from Solomons area to northwest of Fiji and is expected to travel south this week and visit Vanuatu by Saturday and Fiji on Sunday/Monday and maybe Tonga on Tuesday

15 Sep local.  Minor branch between Tuvalu and Tokelau is expected to be strongest around local Thursday 10 Sep. Avoid.

 

STR= Sub-tropical Ridge

The HIGH that is in the Tasman Sea on Sunday 6 UTC is expected to travel east along 30S, crossing northern NZ on Tuesday. It is a weak HIGH and does not have a squash zone on its northern side.

Next HIGH (now crossing South Australia) is likely to be more intense and move into the Tasman Sea on Thu 10 UTC, then travel rather slowly NE,

crossing northern NZ on Wed 16 Sep UTC.  

This HIGH is likely to have a squash zone of strong SE winds on its northern side in the Coral Sea from Friday to Sunday.

Such a slow-moving HIGH offers a good opportunities for sailing to/from NZ/Australia or across the Tasman Sea in quiet conditions.  This may be the last such opportunity for a few months, as El Nino conditions often bring strong SW winds to the Tasman Sea area especially during Sep to November.

 

NZ

The Low we had over last weekend is still intensifying to SE of NZ on Monday, affecting Chatham Islands.

Tuesday is expected to be the day this week with sunshine and light winds,  but a frosty start in many inland places.

On Wednesday a LOW is expected to form in mid-Tasman Sea.  This is expected to intensify as it crosses NZ on Thursday along with strong northerly winds, and further deepen to east of the North Island on Friday/Saturday/Sunday—a typical event sometimes called an “olde man Southerly’ lasting three days and bringing intense rainfall to eastern North Island.

>>>>>> 

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com. Tell anyone you like that to subscribe they should email me.

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.

To unsubscribe from WordPress: click the "unsubscribe" link on the bottom of the email. Or, if email wasn’t from WordPress then send a reply email saying LEAVE.

 

 

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