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

23 June 2019

Bobgram

WEATHERGRAM

YOTREPS

Compiled Sun 23 June 2019

 

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.

 

Solstice was Friday 21 June 1554UTC, but for the next six weeks, as the days’ get longer in NZ the cold gets stronger.

 

Tahiti to Tonga

Now that many yachts are about to travel west from Tahiti to Tonga, it is time to review the weather, in general terms, for this route.

Getting from the Tahiti area to Tonga/Fiji means crossing the South Pacific Convergence zone, SPCZ

 

1. This zone may be weak or may contain squally showers. In the models it is portrayed as a zone of light winds. To see a forecast for this zone, use windy.com and rain accumulation 5 days.

This zone may linger in the north (it does this in an El Nino, and we are nearly in an El Nino), or, it usually hovers between Samoa and Southern cooks. To avoid it choose a different latitude or aim for gaps in the zone.

2. Another thing to avoid is a SQUASH ZONE, when a large High travels east along 30S.

When the central pressure in the High is 1030hpa or above, it gets dirty (above ten thirty is dirty) and squeezes the isobars north of the high in the trade wind zone closer together making a "squash zone" of enhanced winds and rough seas. These usually occur around 20 to 25 South, and may last for several days. They are reasonably easy to forecast, and are worth avoiding. If caught in one, change your latitude rather than your longitude.

3. The third thing to avoid is the passing trough or passing low.

The systems tend to form on the SPCZ and travel southeast along it, propelled by upper NW winds as a steering field. They also tend to have their own mini-squash zones. Isobars give a clue about the intensity of a passing trough: those above 1010hP are usually weak and those below 1007 are worth avoiding.

There are three routes between Tahihi and Tonga, northern, central and southern:

The northern route goes via Suwarrow to Samoa and can be used when the SPCZ is further south

The middle-route offers stopovers such a Palmerston Island and Niue and is a good alternative when the SPCZ is further north than normal.

The southern route, going via Rarotonga and maybe Beveridge reef, is not often used but may help avoid a squash zone or sometimes a passing trough.

Basically, avoid passing troughs and squash zones, and go thru the SPCZ when it is weak. This may mean taking short hops rather than getting direct from Tahiti to Tonga in one go.

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THE TROPICS

TC VAYU brought moderate damage to NW India last week when it made landfall. It was the strongest cyclone in this area for 21 years. ( 8 fatalities and 12 injury reports).

The latest cyclone activity report is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

There are areas of potential development near the Philippines and to north of PNG, also off the west coast of central America.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ stretches from Solomons to near New Caledonia to south of Tonga this week. A weak passing trough (down to 1016hPa) is expected to travel southeast along this zone to east of New Caledonia and south of Tonga on Mon/Tues, and then another stronger passing trough is likely in the New Caledonian /Fiji this weekend (down to 1004, worth avoiding).

 

Subtropical ridge (STR)

HIGH 1028hpa is expected to travel along 30S to south of Tahiti next few days—with a small squash zone near Southern Cooks.

Large HIGH is expected to slowly travel along 40S this week, reaching 1040 hPa over South Tasman Sea on Thursday, and crossing central NZ this weekend. There are likely to be squash zones between NZ and New Caledonia/Fiji with this High.

 

Tasman Sea /NZ/Aus

Weak trough is expected to linger around North of NZ on Monday/Tuesday with light winds and scattered showers.

After that the winds north of NZ are easterly, increasing to strong in squash zones. Avoid. Should be Ok for getting to Australia , not the other way.

HIGH is expected to be followed by a trough in the Tasman Sea next week.

 

Tahiti to Tonga

Trough now moving off to east of Society Islands. Small squash zone west of Tahiti on local Monday. Weak passing trough over Tonga on Tuesday 25 traveling east to be south of Southern Cooks local Thursday.

Next passing trough expected to reach Tonga this weekend, worth avoiding.

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If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>>

16 June 2019

Bob Blog 16 June

WEATHERGRAM

YOTREPS

 

Compiled Sun 16 June 2019

Bob McDavitt’s ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world.

 

The South Pacific Convergence Zone explained

Now that many yachts are about to travel west from Tahiti to Tonga, and are thus about to sail thru or around the SPCZ, this obstacle has become a talking point…as if it guards the eastern entrance to the South Pacific like a protective dragon, and some have asked what is it, why is it there, how does it differ from the ITCZ and what makes it tick.

 

Weather is a mix of pattern and chaos, and meteorological teaches concentrate on the pattern. In tropical meteorology the first idea given is the Hadley cell.

 

Because the sun is most directly overhead at the equator, that’s where the warmest seas are, and this causes rising air. Once the rising air reaches high enough it spreads outwards and sideways to the north or south, where it sinks at dries out. The sinking air reaches the surface again around 30N or 30S (subtropical ridge) and then recirculates back to the equator as surface winds know as trade winds. The trade winds from each hemisphere converge together in a zone, and this convergence narrows the zone of rising air into a feature called the Intertropical Convergence Zone or ITCZ

 

But in the Southern Hemisphere, the Andes of South America cause a split in the trade winds. They block a HIGH near 30S around 90 to 110W, or near Easter Island. It is quasi stationary, just like the High between California and Hawaii, and also has a gyre that is collecting a rubbish heap just as badly (see Henderson island). blogs.fco.gov.uk/lauraclarke/2018/04/10/henderson-island-plastic-pollution-in-paradise/

 

1. There are easterly winds on the north side of this “Andes” High: they are dry due to continental outflow from off South America. These easterly winds travel well to west of the dateline along around 10 to 15S.

 

2. And there are migratory Highs that travel east along the subtropical ridge from Australia to east of NZ, with a zone of south to southeast winds on their northern side. These South/SE winds come and go according to the migratory high and are usually found around 15 to 25S.

 

3. The convergence zone between these easterly and Southeasterly winds is called the South Pacific Convergence Zone, or SPCZ.

 

It is typically located from the Solomon Islands southeastwards to the Southern Cooks, but sometimes may have large gaps or be very quiet.

 

It is affected by many things: the PDO which takes many years to switch, by the El Nino/La Nina which last a year or so, by the strong annual cycle which makes the seasons, and by the MJO which comes for a week or so every six weeks or so.

See the diagram at  www-gte.larc.nasa.gov/pem/pemt_flt.htm

 

I have found that the easiest way to determine the position and severity of the SPCZ is to use satellite imagery, and the easiest way to decide what it may do over next few days is to use the 5day rain accumulation parameter on windy.com.

 

Read more about it at en.wikipedia.org/wiki/South_Pacific_convergence_zone

 

THE TROPICS

TC VAYU is in the Indian ocean and weakening and about to make landfall over NW of India.

The latest cyclone activity report is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

There are areas of potential development in China sea and North of PNG, also off the west coast of central America. This week.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ stretches from Solomons to Tuvalu and Samoa this week.

A trough is expected to travel across Southern Cooks and Tahiti late in the week.

 

Subtropical ridge (STR)

HIGH over South Tasman Sea is expected to cross New Zealand on frosty Tuesday and then travel to east of NZ.

Next High is expected to spread into Tasman Sea next week.

 

Tasman Sea

Low is expected to deepen east of Coffs on Monday and then travel east and weaken, with associated front crossing NZ on Thursday followed by a westerly flow on Friday.

This Tasman trough is likely to replace the trade winds over northern Tasman Sea with light winds or SE winds, good for getting from Australia to Noumea, but not the other way.

That Tasman trough is expected to cross NZ on Thursday so the last good day to depart NZ for the tropics is Tuesday, and even that will need waypoints to zigzag across a period of northerly winds on Wednesday and Thursday.

 

Tahiti to Tonga

A passing trough is expected to affect Southern Cooks on local Tuesday and maybe the Tahiti area on local Thursday. Departures from Tahiti until Wednesday should be able to avoid that trough and have trade winds for a while. Passing trough expected to reach Tonga by local Tuesday 25 June.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>>

 

 

09 June 2019

Bob Blog 9 June 19

WEATHERGRAM

YOTREPS

 

Compiled Sun 09 June 2019

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’s the El Nino?

The state of the ENSO =almost an El Nino at times

 

The Atmosphere:

 

El Nino and La Nina are opposite ends of the swing of an identifiable tropical influence on our seasonal weather: the La Nina, caused by cooler than normal seas along the equatorial eastern pacific. shifts the subtropical ridge away from the equator, and the El Nino, with warmer than normal seas, draws the subtropical ridge closer to the equator. Their comings and goings can last several months, maybe over a year, and so their status can be used to help forecast the weather for the coming season.

 

ENSO = El Nino/Southern Oscillation. The main parameter we watch from the atmosphere is the Southern Oscillation Index SOI (30 day running mean) as it sums up the whole weather pattern over the South Pacific in one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin, in other words it counts the average number of isobars between them on the weather map. When the SOI is more than plus one (standard deviation from its mean) for more than a month we call it a LA NINA event, and when it stays more than minus-one we call it an EL NINO event.

 

Since February the SOI has been negative, and for a while in March was touching a weak El Nino. Since then it has weakened, but in the last week it is touching into El Nino again. If it continues as negative as this then the South Pacific may be in for weaker trade winds and more SW wind events than normal

Near El Nino conditions are seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekly

(Note that in this graph on the vertical axis 10= 1 standard deviation)

 

The Ocean:

NINO3.4 is a region in the eastern equatorial Pacific Ocean that acts as a heat storage area during an El Nino or becomes cooler than normal during a La Nina. This plays with the heat budget of the atmosphere and thus with the weather patterns.

At the farmonline web site we can see the trend in the sea surface temperature in the NINO3.4 area. The diagram shows the weekly temperature anomalies since Jan 2016. Since then there has been several cool periods. Sea has warmed since May 2018 and touched El Nino territory late last year and in Feb/March 2019 and since then has been relaxing, Data missing for May and June. The ocean has not been in tandem with the atmosphere.

Near El Nino at times are seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=nino34&p=monthly

 

The International Research Institute of the Climate Prediction Centre compiles data from several ENSO prediction models. The model predictions for the Nino 3.4 SST anomaly is that the seas should stay much the same for the next few months but may warm a little more between the coming October to January period.

CPC/IRI predictions  are at iri.columbia.edu/our-expertise/climate/forecasts/enso/current/

 

The latest SST anomaly map from www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html shows lots of warm anomalies across the entire tropics, except for NW Australia and the Humboldt current off South America.

 

THE TROPICS

There are no cyclones at present, but there is potential off the central American west coast and about the south on India. The latest cyclone activity report is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ stretches from Solomons to Fiji and Tonga this week. A trough is expected to travel across Fiji and Tonga on Monday to Wednesday and then to travel off to the southeast.

 

Subtropical ridge (STR)

HIGH at 30S to north of NZ on Monday is expected to travel slowly east.

Next HIGH is expected to enter from Australia into Tasman Sea on Tuesday and slowly cross the Tasman Sea to ne north of NZ on Saturday.

 

Australia to Noumea

With the near southerly winds ahead of each of these Highs there is a brief opportunity for sailing from Australia to Noumea, departing Monday or Friday/Saturday.

A passing trough crossing the Tasman Sea on Tuesday and Wednesday may  impede a voyage from Noumea to Australia.

 

NZ to tropics:

Monday departure should be OK to go around the back side of the trough that is crossing Fiji and Tonga Monday to Wednesday, and trips to Tonga are able to avoid the larger swells from the Tasman Sea. Trough is expected to cross Northland on Tuesday night /early Wednesday, Stay put for that, but should be OK to depart in the SW flow that follows

 

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If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>>

 

02 June 2019

Bob blog 2 June

WEATHERGRAM

YOTREPS

Compiled Sun 02 June 2019

 

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.

 

REVIEW of MAY

Sea Surface temperature anomalies as at end of April may be seen at

www.weatherzone.com.au/climate/indicator_sst.jsp?lt=global&lc=global&c=ssta

 

The main pattern changes are a slight warming around New Caledonia and slight reduction in the warmth of the Tasman Sea, a warming in the India Ocean, warming in the Humboldt current off western South America, and a reduction in the warmth of the North Atlantic. The Caspian Sea and Black Sea are outstandingly warmer than normal.

Another month that has been mostly warm, with the main cool areas being melt water around the Arctic or Antarctic.

 

To see how the annual weather cycle and the seasons are working out, we csn check the average isobar maps for past 30 days and their anomaly from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

The subtropical ridge has started its northern shift in both hemispheres. This has allowed troughs to develop in the South Tasman Sea. The near equatorial trough has also drifted north, especially over India. But the Indian Monsoon is only now starting and is about a week late, as seen at

www.imd.gov.in/pages/monsoon_main.php. A late monsoon encourages a heat wave over northern India, and sure enough today’s high is 45C

 

Zooming into the NZ area, and comparing monthly anomalies for end of May with end of April, shows that the subtropical ridge STR has moved north as shown by the northern 1015 isobar over Queensland. Also, the STR has weakened in the South Tasman Sea with the 1015 isobar shifting from 50S to 40S. The westerly winds over NZ are increasing.

 

THE TROPICS

There are no cyclones at present, but there is a tropical depression off the central American east coast. The latest cyclone activity report is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is rather weak and mainly from Solomons to the Tokelau area this week, north of Samoa.

There is also an active convergence zone lurking to southeast of Tahiti around the Gambier Islands.

 

Subtropical ridge (STR)

HIGH at 30S to north of NZ on Monday is expected to travel quickly off to east.

Next HIGH is expected to enter from the west into the south Tasman Sea on Friday and travel across central NZ on Sun/Mon 9/10 June.

 

Australia to Noumea

Travelling Tasman Trough expected to break the trade winds and reach Noumea around Wednesday, followed by southwest/South winds and big swells  on Thursday, then the trade winds return.

 

NZ to tropics:

Stay put until Friday or Saturday.

A Low is expected to develop off Sydney on Monday and deepen into a large system with a Low of 986hPa on Tuesday, then cross the North Island on Wednesday, followed by a cold and vigorous SW flow from the Antarctic over NZ on Thursday, slowly easing on Friday.

Departures to the north from NZ may be possible on Saturday (perhaps for some from late Friday).

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>> 

26 May 2019

Bob Blog 28 May 2019

WEATHERGRAM

YOTREPS

Compiled Sun 28 May 2019

 

Bob McDavitt’s ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world.

 

THE TROPICS

The 3pm analysis from Fiji Meteorological Service today shows some convergence zone, a band of trade winds, and that Big fat High we mentioned last week is now moving off now to east of NZ.

 

There were around 20 yachts caught in North Minerva reef is last week s squash on. It’s easing now and yachts are stirring to get to Fiji (or Vanuatu). Eastely swell around the area was 3.5m 7 seconds earlier today, and is still around 2.7 m tonight, expected to ease to 2.3m on Monday.

 

The winds are expected to be from NE in the area on Mon/Tue/Wed, turning to light SW/W/NW on Thursday/Friday, so those heading for Tonga should wait for this weak passing trough until Thursday and then have a few days of tail winds.

 

Voyages to Suva or places further west may be able to take off on Monday. As for Savusavu, may be able to go on Mon or Tue, fall off to the west in the NE winds and when they finally swing easterly further north, go more direct

 

There are no cyclones at present, but there is p tropical depression off the central American west coast. The latest cyclone activity report is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is mainly from Solomons to the Samoa area this week.

There is also an active convergence zone lurking to south of Tahiti and the Society Islands.

 

Subtropical ridge (STR)

HIGH now east of NZ is expected to linger swell south of French Polynesia this week with a squash zone of enhanced trade winds on its northern side until Wednesday.

 

Australia to Noumea

From Brisbane area to New Caledonia: There are useful Southwest to south winds from Mon to Thursday.

 

NZ to tropics:

A series of troughs is expected across Tasman Sea and NZ this week.

One front is expected to visit Opua on Tuesday, and the local forecast is for northwest winds rising to 25 knots on Tuesday morning with rough sea, easing early Wednesday to southwest 15 knots. So, a Tuesday departure might have a bumpy start.

However, this may change, and, depending on tomorrow’s data, a Tuesday departure might be better than a Wednesday departure.

Next trough is likely to bring strong disturbed westerly winds to Northland from Thursday 30 until at least Queen’s Birthday Monday.

A Wednesday departure should be able to get far enough north to avoid these strong winds.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>>

19 May 2019

BobBlog 19 May

WEATHERGRAM

Compiled Sun 19 May 2019

 

Bob McDavitt’s ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world.

 

THE TROPICS

There is a tropical low NW of Fiji, called TD12F by Fiji and 95P by Guam, slowly drifting SE. It is expected to visit Vanua Levu on Wednesday and may either then linger as a trough somewhere near Fiji, or drift off SW towards NZ, or fade where it is. At this stage I’m not sure which option it may take.

 

Viewable at www.met.gov.fj/index.php?page=trackmap

 

It is quite active at present as seen at www.meteo.nc/nouvelle-caledonie/observations/images-satellite and there is a possibility it may be be briefly named as a Cat 1 cyclone

But it is in a moderate sheared environment  (differing winds which tend to rip it apart) and there is high shear on its south side with dry air, which means as it comes south it dies. See www.met.gov.fj/aifs_prods/20036.txt

 

If it’s remains linger to east of Fiji then we have the makings of a squash zone between Tonga and Minerva

 

A HIGH is expected to travel east along 35S from NZ eastwards from Friday 24 May to Wed 29 May. It is the combination of this High and that lingering trough which is expected to make a squash zone with strong E to SE winds and rough seas near Tonga to Minerva from Friday 24 May until maybe the middle of the following week. This squash zone is worth avoiding.

 

The squash zone may be seen at windy.com

 

There are no cyclones at present. The latest cyclone activity report is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

No cyclones around, but it interesting to see some potential off the Nicaragua coast so early in their season.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ has weakened into three different zones: one in the Coral Sea, one over Tuvalu by mid-week, and the third, with today’s depression NW of Fiji shifting to between Samoa /Niue and Tonga by mid-week.

 

HIGH is expected to travel east along 30 to 40S across Tasman Sea from Monday reaching NZ on Thursday then going further east of NZ from Friday 24 May until early/mid the following week. There is likely to be a squash zone of strong SE wind sand rough seas on the north side of this High between Tonga and Minerva next weekend. Avoid.

 

Australia/Tasman Sea / New Zealand

From Brisbane area to New Caledonia: Trade winds weakening on Thu/Fri and may be light winds/southerlies from Friday 24 to Tuesday 28 May offering a reasonable voyage.

From NZ to tropics: Departures early in the week to Tonga are likely to encounter squash zone near Minerva/Tonga due to combination of a stalled trough near Fiji and a HGH travelling to east of NZ late this week. Better to stay-put until squash-zone threat weaken.

Possibly Ok for getting to Fiji and looks good next few days for departure to New Caledonia.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>> 

 

 

12 May 2019

Bob Blog 12 May

WEATHERGRAM

YOTREPS

Compiled Sun 12 May 2019

 

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.

 

We can now say that the 2018/2019 Cyclone season is nearly over.

There has been one last “cyclone” named today as ANN located west of New Caledonia and going west. It seems to have managed to make the threshold for being a tropical cyclone, in the lowest category 1, but is expected to weaken back to a tropical depression by Tuesday.

 

During the past week there has been the passage of an active phase of MJO or Madden Julian Oscillation across the South Pacific. It takes 10 to 20 days for the active part of an MJO event to travel across the Pacific (a burst of extra convection that can trigger cyclones). Since this MJO event is now expected to move off, we are likely to have a more subdued South Pacific Convergence zone over the next few weeks.

 

Another parameter that helps us watch pattern sin the tropics is Outgoing longwave radiation or OLR. When the tropical convergence zones are active their cloud blocks radiation from escaping to outer space, and OLR is low, coloured blue (for bubbly). When skies are clear radiation can escape to outer space and OLR is high, coloured orange or (mellow) yellow.

 

A constructed analogue forecast of future values of the OLR show that we are expected to have a phase of high OLR (orange values) over the next few weeks, and that means a subdued South Pacific convergence zone.

See diagram at www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/forca.shtml

 

=-=-=-=-=-=

THE TROPICS

Latest cyclone activity is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential as seen at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

TC ANN was named today and is expected to weaken as it moves of to the west.

No other cyclones around.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to weaken this week in the Coral Sea, and to be most active this week between Tokelau (north of Samoa) and Southern Cooks.

 

Subtropical ridge (STR)

New HIGH is expected to travel east along 30S across Tasman Sea on Mon and Tuesday and fade on Wed.

Next HIGH is expected to travel east along 30S across Tasman Sea from Thursday, crossing central NZ on Sat/Sun 18/19 May, followed by active trough on Sun/Mon 19/20 May.

 

Australia/Tasman Sea / New Zealand

Looks OK for departure from NZ to Tonga/Fiji/Noumea on Tuesday/Wednesday 14/15 May.

A Monday 13 departure may have a bumpy start in left over northerly swell.

After Wed, stay put or may encounter some NE winds.

 

Fast moving active FRONT is expected over Tasmania on Monday and NZ on Tuesday/Wednesday followed by large swells around NZ on Thu to Saturday.

 

As that front crosses the south Tasman Sea on Tuesday, there is a brief twist to southerly in the winds between Queensland and Noumea—offering possibilities of sailing to Noumea, then again a Fri/Sat departure is looking possibly better than a Tuesday/Wednesday/Thursday departure.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>>

05 May 2019

Bob Blog

WEATHERGRAM

YOTREPS

Compiled Sun 05 May 2019

 

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.

 

REVIEW of APRIL

Sea Surface temperature anomalies as at end of April may be seen at www.weatherzone.com.au/climate/indicator_sst.jsp?lt=global&lc=global&c=ssta

The main pattern changes are a slight reduction in the warmth of the Coral and Tasman Sea, a shifting to south of Australia of the cool pool that was in the South Indian Ocean, and the growth of some cool water in the Humboldt current off the west of South America.

It is sad to see these maps are mostly warm, and that the cool areas seem mainly to be melt water around the Arctic or Antarctic.

 

To see how the annual weather cycle and the seasons are working out, check the average isobar maps for past 30 days and their anomaly from www.esrl.noaa.gov/psd/map/images/fnl/slp_30.fnl.html

The subtropical ridge has had a strong month around the Sothern hemisphere, and has been split into three in the northern hemisphere. The lower than normal pressures to south of Australia are interesting.

Zooming into the NZ area, and comparing monthly anomalies for end of March with end of April, shows that the main difference is the building of High pressure over Australia, and a slight weakening of high pressure east of NZ. This means there has been a switch over NZ from mostly NE winds to mostly SW winds.

 

The last 30 days of rainfall, and its anomaly are seen at trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html

This web site seems to be having problems at present and latest data is 23 April.

Some tropical cyclone tracks in the Indian Ocean stand out. The ITCZ has been wetter than normal across Micronesia, and below normal near Galapagos. There is a “mirror Convergence Zone” along 5degrees south in the Eastern Pacific. There are dry patches appearing in the South Pacific.

 

-=-=-=-=-=-=-=-=-=-=

THE TROPICS

TC FANI has finally weakened after devasting parts of the NE coast of India.

The active phase of MJO is travelling into the western pacific this week.

There are no tropical cyclones around tonight, but there are potential areas for development mainly around north Coral sea and Micronesia. The GFS model currently is running away with the idea of a Tropical cyclone forming in the Coral sea by mid-week and maybe developing and curving counter-clockwise around New Caledonia this weekend. The EC model has a low, but it is weaker and later. Each new GFS run over the past few days has been delaying things, and that is a sign that it doesn’t have a good grasp. The models disagree a lot at this stage, and there is uncertainty until their scenarios get closer.

TC in the tropics at present, with latest cyclone activity may be seen at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is expected to intensify in the Coral sea this week, and spread south. The models agree that a tropical Low forms by around mid-week, but disagree as to if/when it deepens and how fast it travels south. Should be a branch of SPCZ from Samoa to Southern Cooks.

 

Subtropical ridge (STR)

HIGH over 1030hPa traveling around south of South Island tonight is expected to then go NE along 45 to 40S east of NZ. This high should block the troughs in the Tasman Sea until this weekend.

 

Tasman Sea troughs

Low is travelling south into the South Tasman sea on Monday and fading by Wednesday.

Next Low is expected across Bass Strait by Thursday and then across NZ by Sunday 12 May=Mother’s Day.

 

Australia to New Caledonia.

If the GFS model is correct, then a low from the tropics may curve around New Caledonia 11/12 May. That’s no good. Stay put and hope for something better next week.

 

NZ to Fiji/Tonga

With such a dominant High to east of NZ there is a possible departure on Monday, but after that there is too much NE wind between NZ and the tropics until that trough crosses NZ on Mother’s Day. There maybe a good enough departure next week, but unsure at this stage.

 

Panama to Marquesas

Light variable winds in the Gulf of Panama for a motoring start. Then mainly SW winds between 5N and Galapagos area so some tacking may be required for that. Trade winds from the SE are likely for west of around 100W so that’s when to turn to Marquesas.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>>

 

28 April 2019

Bob Blog 28 April 2019

WEATHERGRAM

YOTREPS

Compiled Sun 28 April 2019

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.

 

Another Amateur Radio or HAM network for sailors around the Tasman Sea is TONY’S MARITIME NET

Daily at 2100UTC (9am NZST) on 14315USB.

The net was started about 40 years ago by Tony, ZLIATE (now a silent key) and in those early days boats could be heard from the other side of the world. With the sunspot cycle being at its low, that is no longer possible but we seem to manage.  This is a very friendly amateur radio net that provides a means of communication between maritime mobiles and land-based stations. There are net controllers on both sides of the Tasman and all stations relay reports when conditions are poor.

-=-=-=-=-=-=-

Jonathan Robinson the Fleet director  of SEA MERCY has asked me to add their 20 page web  link to my weathergram this week: imags.com.au/sea_mercy/

Basically, SEA MERCY continues to help around the South Pacific with health care from a floating clinic  and help from sailing vessels volunteering to deliver medical aid to villages affected by cyclones.   There are other Sea Mercy programs offering disaster relief, Education and Economic aid.

It is a registered USA charity based in Oregon, and has developed key international partnerships.   Sea Mercy Fiji operates from Port Denarau, and Sea Mercy Australia was established in Dec 2017.   It is looking for more volunteer yachts, so if you feel the urge the check out this web site.

-=-=-=-=-=-=-=-=-

Another example of chaos: both from weather and a whale in short succession:

From Graham ad Gina on SV SUPERMOLLI

We were off 50 miles East Cape (NZ), Tues 16 April, around 1100hrs when we encountered 2 closely following event You will see the results of a rogue wave and a Whale in the attached photos, all this occurred in about a five-minute period. Bit spooky you see but we are here to share the event by Pic's taken after.

No one hurt, Gina was down below and flew horizontally across the cabin but managed to grab the bridging grab rope we have installed across U Dining area wings. See the Knife and onion peel in the ceiling, not good housekeeping

 =-=-=-=-=-=

More chaos- SV Flying Fish was hit by a rogue wave on Wed 24 April between NZ and Fiji

Read the blog at flyingfishsail.wordpress.com/

-=-=-=-=-=-=--=-=-=-

And here’s a call for a watch for a drifting yacht:

Yves Jaegar was sailing his 44ft Oceanis Beneteau SV FETIA UO UO” when it was hit by a storm on September 3, 2018 between Fakarava and Tahiti. He was rescued by the JRCC of Papeete and had to abandon his sailboat.

Since then, so far, there has been no news of his boat – it probably drifted across the Cooks Islands and Samoa/Tonga, and may now be further west.   If you have heard something please contact <yves.jaeger.at.mail.pf>

(replace the .at. with @, I wrote it this way to stop Yves getting spam)

-=-=-=-=-=-=-=-=-=-=

THE TROPICS

After a few quiet weeks the MJO active phase popped up in the Indian Ocean and has triggered Three Tropical cyclones.  KENNETH has now weakened by has brought wide spread damage to Mozambique--- one month after the damage from TC IDAI.  Warmer than normal seas.

FANI seems to be heading to East coast of India or maybe Bangladesh. BEWARE. 

 LORNA should travel south over open sea.

TC in the tropics at present, with latest cyclone activity may be seen at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

MJO’s active phase in the Indian Ocean last week may cross northern Australia this coming week and  reach the Western Pacific in a few weeks (and weaken) see www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml

WEATHER ZONES

 

SPCZ has moderate intensity from PNG/Solomon Islands to Northern Vanuatu and north of Fiji, and may occasionally visit Samoa.

A trough with squalls between Fiji and NZ tonight is expected to travel southeast over next few days. The trough is likely to reach French Polynesia (Tahiti and Tuamotu Group) on local Tuesday to Thursday this week along with enhanced E to NE winds.  Avoid.

 

Subtropical ridge (STR) /  Australia

HIGH over 1030hPa to east of 160W should travel only slowly east along 35 to 40S this week with enhanced E to NE winds on its northern side.

HIGH is expected to travel east across central Tasman sea from Monday to Friday, maintaining enhanced SE winds between New Cal and Australia until Thursday.  On Thursday/ Friday a trough is expected to travel east across NSW and Southern Queensland, followed by a period of lighter southerly winds which may provide a good enough weather pattern for departing from Australia to Noumea—depends on your boat speed.

South of this passing High there should be an opportunity for a voyage for Hobart to NZ.

 

Tasman Sea/ New Zealand

Trough is expected to cross the North island on Monday followed by a southerly to SE flow. 

 So, from Wednesday to Friday there should be an OK start for a voyage for NZ to the tropics

Trough is expected to travel east across NSW on Fri/ Sat  4/5May and then travel east across South Tasman Sea and Southern NZ from Sun 5  May to Tuesday 7 May.

 

Panama to Marquesas

Gulf of Panama is expected to have some northerly winds this week, so it’s ok to go.  ITCZ between 5N and 3N seems to be having a quiet time this week, after a few squally weeks.  Some calm zones. The variable zones of SW winds on the way to Galapagos are becoming more dominant.    S to SE trade winds from 5S 100W to Marquesas.

 

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>> 

21 April 2019

Bob Blog 21 April

WEATHERGRAM

YOTREPS

 

Compiled  Easter Sun 21 April 2019

Happy Easter .

 

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.

 

Here is an addendum to last weeks tips for cruising yachts:

1. If you are subscribed to or following weathergram@cruisersat.net or weathergram_short@cruisersat.net, then, if you wish to only receive the weathergram (and not messages from other users) you can mute other calls by sending MUTE ON to the net address. To unmute, send MUTE OFF.

2. Note that Gulf Harbour Radio ZMH286 runs independently from YiT. It is NOT necessary for boats to be on YiT before they can talk to Gulf Harbour Radio. If you are registered with YiT then you can send your reports to send@yit.co.nz and they can be seen by Gulf Harbour Radio. Also Gulf Harbour Radio has a net on cruisersnet, see cruisersat.net/nets.

3. The Windy.com app (free of charge) has a planned route plot option.

To make one: "right click" anywhere on the map, this will open a small context window;

- choose "Distance & Planning"; - place your points on the map;

- in the "table of points" you just made, click the button label "share" in the bottom right corner;

- copy the short url link provided or the long URL in the top of your browser and "voilĂ "!

You can also make one by building the URL manually if you are familiar with this.

Each time you plug this "short" or "long url" in your browser, Windy will show the map and your planned route.

4. YiT, Yachts in Transit, at www.yit.nz has a smart phone app, and offers a subscription service to plot your reports and blogs on the web and to request weather information via coded emails. They also provide info on how to use iridium Go!, YB Tracking or Garmin inReach for communications.

5. Saildocs also offers High sea forecast via email:

Send an email, no subject necessary, to query@saildocs.com with message

SEND nadi.sopac or SEND nz.subtrop

6 Fiji Fleet code. Can get a manual weather analysis map via EMAIL.

To download the latest Nadi Fleet code send an email to query@saildocs.com, no subject needed, saying SEND nadi-fleetcode.

Or SEND https://tgftp.nws.noaa.gov/data/raw/as/asps20.nffn..txt

This can be viewed with the Fleet Code plug in OpenCPN.

Open the email and (on a PC) <Right> click on the data, <copy> or CTRL-C. Then, in OpenCPN’s Fleet code plugin, there are 4 options: Files, Text, Raw and Downloads. Select Raw and <paste> or CTRL-V. Voila!, the map appears.

I still have a copy of the old, no longer supported, Fleet code viewing program called PhysPlot. If you want to try it, let me know.

7. AIS: the AIS system allows tracking via relay and via Satellite, but the display online of that oceanic data is restricted by subscription to sites such as marinetraffic.com.

=-=-=-=-=-=

 

THE TROPICS

It id quiet in the tropics at present, with latest cyclone activity seen at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

The monsoon that was active over northern Australia last week has dissipated, and the transition to the dry season is underway. There is a weak pulse of MJO over the Indian Ocean.

Rain in the past week continued strong over Vanuatu, and built in the Indian Ocean. The “mirror CZ” continues just south of the equator in the eastern Pacific, affecting those sailing between Galapagos and Marquesas.

For rain in the past two weeks see trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ has been active between Vanuatu and Fiji, but this section is expected to waken this week. The SPCZ is expected to build in activity along about 17S from Fiji to Tahiti. 

A trough in the northern Tasman Sea is expected to travel east across New Caledonia tonight and during Monday and then fade on Tuesday.

 

Subtropical ridge (STR)

HIGH to east of NZ is expected to travel east along about 35S.

HIGH in mid-Tasman Sea on Monday is expected to stay pit until it is reinforced by another High on Wednesday and then fade as it shifts north to 30S by Friday, allowing westerly winds to also shift north.

 

Australia/Tasman Sea / New Zealand

A slack low is expected to bring heavy shower activity to northern NZ on Monday and Tuesday and travel off to the east on Wednesday then southeast on Thursday.

Deep Southern Ocean Low is expected to travel east along about 55S to south of Tasmania and Tasman Sea from Thu to Sat with vigorous west to SW winds as far north as 35S and large swell going to 30S. Avoid.

North of 30S winds are expected to be mainly from east or SE, Ok for going from Noumea to Australia.

 

Panama to Marquesas

Gulf of Panama is expected to have northerly winds this week, so it’s ok to go. ITCZ has been active between 6N and 3N. This week it is looking OK to go to NW of Galapagos and then SW to around 5S 110W.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>> 

14 April 2019

Bob Blog 14 April 2019

WEATHERGRAM

YOTREPS

Compiled Sun 14 April 2019

 

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.

 

Now that cruising sailors are on their final preparations for departing New Zealand/ Australia for the warmth of the tropical Islands, ‘tis is a good time to review the ways to obtain weather forecasts and/or provide position reports when at sea.

 

Let me know if any of this has changed and I’ll add an addendum to my next blog….

1. For those depending on Shortwave radio, ZLM/ Taupo Maritime Radio offer a continuous 7/24 Trip reporting service see www.maritimenz.govt.nz/about/what-we-do/safety-and-response/maritime-radio.asp

The HIGH SEAS forecast for the area SUBTROPIC from MetService is read out in English via ZLM at 0903hr, and 2103hr NZST/NZDT on 6224 and 12356KHz and repeated an hour later on 8297 and 16531 KHz.  A copy of the Radiofax sked is at

www.metservice.com/_/files/marine-surf/radio/radiofax_schedule.pdf

 

2. Northland Radio ZMH292 is owned and operated by Peter Mott and provides a free of charge (donations welcome) check in service on multiple maritime frequencies. Northland Radio tracks vessels and has a formal policy for dealing with a missed check in. To use Northland Radio, operator requires Maritime Restricted Radio Operators Certificate (MRROC). In the maritime radio service, the callsign is assigned to the vessel, and in New Zealand it starts with ZM. See northlandradio.nz/faq/

 

3. Another SSB service is offered by Yachts in Transit. Patricia and David from Gulf Harbour Radio use the web site www.yit.co.nz to keep track of boats that listen to their rollcall/weather service. FIRST You need to register on this web site with your boat and crew details and then you simply email or radio in your position and conditions in preferably each day (send@yit.co.nz or via SSB). These reports are plotted on a webpage for you and your friends.

FROM 1 MAY to 25 NOV, Patricia/Dave is on air, Mon-Fri 07:15NZST on ZMH286 on 8752Khz or 8779KHz or 8297KHz in that order depending on interference. Other frequencies have been allocated for far away yachts. After the reports are taken, at around 07:30 NZST Dave does a round-up of the weather in each island group, including passage weather from east to west. The www.ghradio.co.nz website offer live streaming and has several good background weather and radio/comms articles.

 

4. AMATEUR RADIO / Ham net: PACSEANET is a ham (amateur radio) network providing a free of charge check in service on amateur frequency 14300KHz USB in the 20 metre band (at 0300UTC). To participate, operator needs to hold an Amateur Radio Operators Certificate (General class or above). In the amateur radio service, the callsign is assigned to the licensed operator, so this is a different callsign from using a maritime callsign. In New Zealand amateur callsigns start with ZL. See pacseanet.com. Position reports are received and reported in the well-know YOTREPS format (but missed calls may not be followed up). People onshore can listen in to a transcription of the roll call from the Pacseanet.com website. The net features 17 listening station dotted between Australia and Alabama.

 

5. EMAIL: Those who have access to EMAIL have several options.

Saildocs may be used to relay the text details of a webpage even if you only have email and no access to the Internet.

They are able to order the latest edition of MetService warnings by sending an email, no subject necessary, to query@saildocs.com with message

SEND http://m.metservice.com/warnings/marine

For subtropics use SEND http://tgftp.nws.noaa.gov/data/raw/fq/fqps43.nzkl..txt

This system also works for coastal sailors using a mobile phone with email.

The formula to get a copy of the latest coastal area BRETT via email is to send an email to query@saildocs.nz with message SEND http://m.metservice.com/marine/coastal/brett

A new provider is cruisersat.net--- using sophisticated filters to reduce the text of a weather forecasts and warnings to a pithy TEXTABLE alternative, free of charge to the average user. They also have a forecasting option based on NOAA weather models.

 

6. Smart phone apps: Some satellite phones now provide wifi that allow nearby smart phones to use apps. www.predictwind.com makes good use of this and as an app that supplies forecast model data, observations and, at the Professional Account level, tools for routing and comparing departure dates. It also has a position tracking tool. There is also a Windy.com app (free of charge) and, I think, it has a position tracking option.

 

7. MetBob. See my website to study more of my services at www.metbob.com

WEATHERGRAM (This blog) is available in different ways :

Internet illustrated edition is at metbob.wordpress.com

To get a one-off (text-only) weathergram via email:

 

Via SAILDOCS:

For a one-off: Send an email to query@saildocs.com, no subject needed with message

SEND nz.wgrm

To subscribe: use SUB nz.wgrm (or SUBSCRIBE nz.wgrm)

To cancel: use CANCEL nz.wgrm or UNSUB nz.wgrm or UNSUBSCRIBE nz.wgrm

 

Via www.cruisersat.net

For full text (Ok for Sat Phone or HF SSB with sailmail/winlink)

To subscribe, send email to weathergram@cruisersat.net, no subject needed with message subscribe boatname (replace boatname with name of your vessel, up to 20 characters).

For the whole weathergram reduced to 4 SMS text messages, for Satellite messengers such as Garmin inReach:

To subscribe, send email to weathergram_short@cruisersat.net, no subject needed with message subscribe boatname (replace boatname with name of your vessel, up to 20 characters).

=-=-=-=-=-=

THE TROPICS

Latest cyclone activity as at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential as seen at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

There is a complex gathering of tropical lows to NW of Fiji tonight, and one of these is expected to go off to the southeast, and the others are likely to fade in a few days.

 

Rain in the past week was strong over NW Australia from TC WALLACE, and also across Vanuatu, associated with a a zone of low pressure forming

For rain in the past two weeks see trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

The “mirror CZ” continues just south of the equator in the eastern Pacific, affecting those those sailing between Galapagos and Marquesas.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to be active until mid-week and linger from Vanuatu across Fiji and occasionally across southern parts of Tonga, and should weaken by end of the weak.

 

Subtropical ridge (STR)

HIGH in southern Tasman Sea on Monday is expected to build to 1035hpa over South Island by mid-week and then travel east across northern NZ on Tuesday and then weaken and travel eastwards along 40S. There is likely to be a squash zone of enhanced trade winds on north side of this High near 20S from southern Tonga to New Caledonia, easing after Thursday.

Next HIGH is expected to travel east across Tasmania on Thursday and then across the South Island on Saturday.

 

Australia/Tasman Sea / New Zealand

A week of easterlies to north of 35S, OK for getting to Australia.

Active trough is expected to cross Tasmania on Wed and then over South Island on Holy Thu/ Good Friday (Passover) and then may stall over North Island on Easter Sat/Sun. This trough is something to consider in Easter Sailing.

 

Panama to Marquesas

Gulf of Panama is expected to have northerly winds this week, so it’s ok to go.

This week it is looking OK to go to NW of Galapagos and the SW to around 5 or 6S 100W.

 

Port Vallarta to Marquesas

Best looking northerly winds for departure this week are from Tue to Thu, otherwise light winds.

ITCZ likely between 9N and 5N, and another convergence zone between 4S and 6S.

 

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>> 

07 April 2019

Bob Blog 7 Apr 2019

WEATHERGRAM

YOTREPS

Compiled Sun 07 April 2019

 

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.

 

For those of you who are now planning to depart Australia or NZ for the tropical Islands (after the cyclone season) and would like as assisted passage: here is some contacts.

 

Island Cruising New Zealand are organising a rally from Opua to Tonga. Sadly the registration for this is now full, but if you’d like to join the waiting list then see www.islandcruising.co.nz/ or visit their facebook site at www.facebook.com/islandcruising.nz/ for newsy tidbits

 

And the Down Under crowd are in full swing arranging the GO EAST Cruisers rally from the Gold Coast to New Caledonia/Vanuatu in May 2019 (6 Maty or soon after).

 

For more info see www.downunderrally.com/go-east-rally-2019

 

=-=-=-=-=-=

 

So, when will this cyclone season finish?

 

Nominally, the cyclone season ends at the end of April. At present TC WALLACE is travelling southwest well offshore of NW Australia, and there is a tropical depression travelling westwards near Darwin, so this cyclone season is still with us.

 

One parameter we watch is the MJO or Madden Julian Oscillation. It takes 10 to 20 days for the active part of an MJO event to travel across the Pacific (a burst of extra convection that can trigger cyclones) and we get such a passage around once every 4 to 6 weeks. There have been active MJO events over the Australia/Pacific region during much of December/early Jan, then in late Jan/early Feb, and now in late March/early April. These can be seen as the blue (for bubbly) OLR or Outgoing Radiation zones in a time-longitude diagram from www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/forca.shtml

 

The stage is set for the non-active or settled phase of the MJO to travel across the Pacific over the next few weeks, but there may be another active MJO late in April, so even if the next few weeks are clear of cyclones we can’t say the season is “over” yet.

 

=-=-=-=-=-=-=-=-=-

 

A touch of weather chaos.

I often use the expression that weather is a mix of pattern and chaos, and I use it as a way of explaining away the weather features that the models just do not resolve. I noted an example from the real world near Wellington yesterday, as seen at windy.com

The smoothed-out pattern of the global model isobars did NOT capture a chaotic little whirl of winds that formed to southeast of Cook Strait. This little feature caused a gale of southerly winds through Cook Strait, as seen in the Wind observations. The computed wind forecasts were constantly underestimating the real world.

 

Another thing to note is that the barometer was reasonably steady throughout this gale. This is often the case near a “squash zone” and that is little comfort to a sailor looking for signs.

 

MetService was on the ball, watching weather radar and analysing the reported observations with isobars down to 1hPa apart, they could track this chunk of chaos and incorporate it into marine, aviation and general media forecasts and warnings. The MetService analysis was tweeted at twitter.com/MetService

=-=-=-=-=-=

THE TROPICS

Latest cyclone activity as at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential as seen at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

 

TC WALLACE is staying offshore (fingers crossed) off NW Australia. There is also a low travelling west across the Darwin area, but it is not expected to deepen much further.

 

There are some spots of possible activity this week around Solomon Islands and Micronesia, otherwise all looks quite quiet.

 

Rain in the past week from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif was strongest near WALLACE and around Micronesia and weaker than last week elsewhere around the Pacific.

 

The “mirror CZ” continues just south of the equator in the eastern Pacific, affecting those sailing between Galapagos and Marquesas.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to be most active this week across the north Coral Sea to northern Vanuatu to south of Fiji. There is also expected to be a convergence zone over Nauru and Tuvalu.

 

Subtropical ridge (STR)

HIGH in the central Tasman Sea on Monday is expected to travel east across northern NZ on Tuesday and then further east along 30 to 35S.

Next HIGH is expected to travel east across Tasmania on Thursday and then across the South Island on Saturday.

 

Australia/Tasman Sea / New Zealand

Lots to avoid. Low to east of NZ is travelling slowly south-southeast from Monday to Wednesday, giving a southerly flow over North Island mainly on Monday. Next trough is expected to cross central Tasman Sea on Tuesday, the South Island on Wednesday, and then deepen over North Island on Thursday, with a Low near Cook Strait, and then a southerly flow over the North island on Friday and Saturday.

 

Panama to Marquesas

Gulf of Panama now has SW swells. There are reasonable northerly winds for departure until local Tuesday, and again from next local Saturday, otherwise variable light-ish winds. Now looks better to go around south end of Galapagos rather than the north end, to avoid adverse winds/currents.

 

Port Vallarta to Marquesas

OK winds for departure until local Tuesday, then light winds.

Weak ITCZ likely between 7N and 3N, and another convergence zone near 3 to 4S

 

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>> 

31 March 2019

BobBlog

WEATHERGRAM

YOTREPS

Compiled Sun 31 March 2019

 

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.

 

REVIEW of MARCH

Sea Surface temperature anomalies as at end of March may be seen at

www.weatherzone.com.au/climate/indicator_sst.jsp?lt=global&lc=global&c=ssta

 

The main pattern changes are a cooler South Indian Ocean and a warmer Coral Sea. It may be that fresh melt water from the recent Antarctic summer has gone north into the South Indian Ocean.

Elsewhere the changes are more subtle—even in the target area for El Nino, the eastern equatorial Pacific,

 

To see how the annual weather cycle and the seasons are working out, check the average isobars for past 30 days and their anomaly from www.esrl.noaa.gov/psd/map/images/fnl/slp_30.fnl.htmlclip_image005

There is a strong “WAVE 3” pattern in the southern hemisphere with HIGHS lingering over Southern Indian Ocean, east of NZ, and west of the Andes. Troughs and southerly outbreaks have been encouraged into the Aussie Bight.

The low-pressure anomalies around the Arctic and northern Europe are related to the Polar vortex. And there is still a large anomalous HIGH around the Antarctic.

 

Zooming into the NZ area, and comparing monthly anomalies for end of Feb with end of March, shows that the main difference is the expanding of the HIGH east of NZ with a 1020 isobar pushing the 1015 from 45S to 55S. Further north, the 1010hP (between light blue and dark blue) isobar is in much the same place, but the 1005 that was around Vanuatu and New Caledonia has faded.

 

The last 30 days of rainfall, and its anomaly are seen at trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html

And this shows that even in this monthly averaged image the rain track of TC IDAI into eastern Africa stands out. The ITCZ has been wetter than normal across the central Pacific, and below normal across the eastern Pacific. The “mirror Convergence Zone” along 5degrees south in the Eastern Pacific has blossomed in March. There are dry patches appearing in the South Pacific during the “wet” season.

 

THE TROPICS

Latest cyclone activity as at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential as seen at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

TC JOANINHA continues on its voyge southwards across the Indian Ocean, and has now left the tropics. The probability for cyclone formation is high around the Marshall islands, the Timor Sea , and. Less so, around Solomon Islands.

For rain in the past week, see trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

Rainwas strongest near JOANINHA and between Nauru and Fiji. There was also a drenching day over NZ Southern Alps, with one raingauge measuring over 1000mm of rain but TRMM doesn’t seem to resolve that finely. This rai took out a bridge, see www.facebook.com/watch/?v=342974573228755

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is active over Papua New Guinea and parts of the Coral Sea. A LOW is forming southeast of Niue and expected to deepen as it travels southeast out of the tropics, bringing a few days of vigorous SW winds and swell to Niue and NW winds and rain to Southern Cooks.

 

Subtropical ridge (STR)

HIGH expected to spread across Tasmania on Monday and Tuesday and then to fade in central Tasman sea/ central NZ on Wed and Thurs.

Next HIGH is expected to travel east to south of Tasmania on Thursday, south of NZ on Fri, then to east of NZ along 45S from Sat.

 

Australia/Tasman Sea / New Zealand

Active front expected to cross NZ on Monday followed by a cooler south/SW flow on Tuesday, and then another cold front from the south on Thursday and Friday, dropping temperatures.

 

Panama to Marquesas

SW swells are starting to arrive in the Gulf of Panama. Good northerly winds for departure from Panama until local Wednesday, then light winds and a motoring start.

There is a reasonable tail current to north end of Galapagos, then go to 6S 100W, to avoid the “mirror convergence zone” along around 5 South,

 

Port Vallarta to Marquesas

Light winds for starters over next few days, best winds for departure this week are likely to be after Friday.

Weak ITCZ likely between 6N and 2N, and then a “mirror CZ” near 3 to 5S

 

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If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>> 

24 March 2019

Bob Blog 24 March

WEATHERGRAM

YOTREPS

Compiled Sun 24 March 2019

 

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.

 

An addendum regarding that DECLINATION map which appeared in last week’s blog , is that you can find your solar altitude (local sun angle at solar noon) by computing (for the southern hemisphere) 90-L-D, where L is our latitude in degrees South,  and D is the declination.

(In Northern Hemisphere  it is 90-L+D, where L is Latitude in degrees North).

SO

At the equinox, latitude L of Auckland is say 37 degrees so 90-L-D is 90-37-0 = 53 degrees.

At winter solstice D is +24.5 so 90-L-D is 90-37-24.5= 28.5 degrees

At summer solstice D is -24.5 so 90-L-D is 90-37+24.5= 77.5 degrees

 

MJO What is it and what might it do?

MJO stands for Madden Julian Oscillation, and can be thought of as being a wave of extra convection or shower activity that travels eastwards around the planet, in the tropics once every 30-60 days taking around a week to pass by.

It was discovered in 1971 by Roland Madden and Paul Julian of NCAR (US national centre for Atmospheric research), and as it passes it triggers extra cloud and rain. This wet phase is followed by a dry phase.

The normal diagram used for following MJO is a phase diagram as found at

www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml#forecast

 

In this diagram, the “ Maritime Continent “ is another name for Indonesia/Papua New Guinea. It shows the expected position and strength of the wet phase of the MJO travelling westwards (right to left in this diagram) next few weeks, but one with little strength.

Another diagram we use is the OLR diagram. OLR= Outgoing radiation and is lowest (blue) when blocked by cloud and rain, and highest (yellow/orange) in reasonably clear skies. As a mnemonic, think Blue for “bubbly” and Yellow for “mellow” This diagram shows the wet phase of the MJO having an impact on the western Pacific during the coming week, and then fading as it gets further east.

 

Meteo France have used this data to produce a probability diagram of Cyclone formation during the next three weeks, as seen at www.meteo.nc/nouvelle-caledonie/cyclone/coin-des-experts

These maps reach their strongest probability of a cyclone occurring in the region of TC VERONICA, and second highest but looking rather weak, chance is between New Caledonia and Fiji

 

THE TROPICS

Latest cyclone activity as at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential as seen at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

 

TC JOANINHA is over the open sea in South Indian Ocean. VERONICA is skirting NW Australia, and TREVOR is going inland and has just been downgraded.

The MJO (Madden Julian Oscillation) wave of increased activity is travelling east into the Western Pacific this week, and it is weakening. There is likely to be increased activity between Solomon Islands and Vanuatu/Fiji.

Rain in the past week was strongest near the cyclones. It has weakened a little along the Pacific ITCZ.

See trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

The “mirror CZ” continues just south of the equator in the eastern Pacific, affecting those sailing between Galapagos and Marquesas.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is active over Papua New Guinea and from Solomon Islands to Vanuatu/Fiji this week. A low may form over the Fiji/Tongan area by the end of the week, travelling to the southeast

 

Subtropical ridge (STR)

HIGH to east of NZ tonight is expected to travel slowly east, lingering near 40S 165W. Expect enhanced trade winds on its northern side, between 20 and 30 South.

Next HIGH from Australian Bight is expected to travel east across Bass Strait around Wednesday and around the South Island on Thursday, then off to the east along 45 to 40South.

 

Australia/Tasman Sea / New Zealand

Deep Low is expected to travel southeast across South Tasman Sea from Monday to Wednesday and  associated front should cross New Zealand on Thursday.

A small but intense low may deepen off Sydney on Friday, and then widen outwards and travel south/southeast late this week.

 

Panama to Marquesas

The northerly winds are still over 20 knots at times around Panama, but for a lull on local Monday, and then relaxing from local Thursday.

There is a good tail current to north end of Galapagos, then go to 6S 100W, to avoid the “mirror convergence zone” along around 5 South,

 

Port Vallarta to Marquesas

There is a Tejuantepecer blast forecast to peak from Monday to Wednesday, (for background see en.wikipedia.org/wiki/Tehuantepecer)

However, winds around Puerto Vallarta are likely to be OK for departure anytime this week.

Weak ITCZ likely between 6N and 3N, and then a “mirror CZ” near 3 to 5S

 

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>>

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