Translator

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

17 March 2019

Bob blog17 March 2019

WEATHERGRAM

YOTREPS

 

Compiled Sun 17 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.

 

First, I must tell you all that I (as with the rest of Kiwiland) was shocked and saddened by the senseless killing on Friday in Christchurch. My thoughts are with the victims. I can’t fully concentrate on meteorology when all  this inhumane violence is around, so this week’s blog is a brief one. See Image is from www.facebook.com/YeoCartoons/ (Thanks to Shaun Yeo)

Give help at givealittle.co.nz/cause/christchurch-shooting-victims-fund ($~4millionNZD already donated)

 

Second, since my DNA is apparently 95% traceable to Ireland, I can wish you all a Happy Saint Paddy’s day today. Sláinte

 

EQUINOX

The sun is directly over the equator on Wednesday 20 March 2158 UTC (in NZ that’s Thursday morning around 11am NZDT), and that’s the equinox. Australia, New Zealand and Samoa switch from Daylight or Summer time to standard time on 7 April, the first Sunday in April.

 

World Met Day

Another day worth noting this week is World Met Day on 23 March. This marks the anniversary of the opening of the World Meteorological Organisation as part of the UN in 1950. This year’s theme is THE SUN, THE EARTH AND THE WEATHER

The Sun delivers the energy that powers all life on Earth. It drives the weather, ocean currents and the hydrological cycle.

It shapes our mood and our daily activities. It is the inspiration for music, photography and art.

See worldmetday.wmo.int/en/  for an enjoyable encounter with nature.

 

THE TROPICS

During the past week TC IDAI made land fall over Mozambique and Zimbabwe bringing death and destruction www.bbc.com/news/world-africa-47595863 (over 30 deaths during IDAI after a week of at least 66 deaths from floods). Flash floods in Indonesia over last few hours have killed at least 50 people. It is sad but true, that “Weather is the biggest terrorist on this planet”.

Cyclone track from wunderground is at www.wunderground.com/hurricane/southern-indian/2019/Tropical-Cyclone-Idai

Note that month should be 3 rather than 4.

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 SAVANNAH is over the open sea in South Indian Ocean , and Depression 03W is moving towards Philippines and Depression 92P near Papua New Guinea, is moving toward Queensland.

The MJO (Madden Julian Oscillation) wave of increased activity is travelling east across Northern Australia this week, and so we can anticipate increasing activity in the South Pacific over the next few weeks.

Rain in the past week has intensified around Papua New Guinea and along the Pacific ITCZ west of the dateline. It remains weak elsewhere in the South Pacific.  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 the northern Coral Sea, with a tropical Low 92P having a good chance of becoming a cyclone as it heads towards northern Queensland. Activity on the SPCZ is also expected to intensify between the Coral sea and Vanuatu this week.

The week starts with a Low on a convergence zone between Niue and Southern cooks. This low is expected to move off to the south and that should weaken the shower activity over French Polynesia.

 

Subtropical ridge (STR)

HIGH over southern NZ tonight is expected to travel east along 45 South.

The next two HIGHS are also expected to travel south along around 45 to 50S – it’s that time of year that the HIGHS stay south (the equinox).

This fills half the Tasman Sea with easterly winds good only for sailing west.

 

Australia/Tasman Sea / New Zealand

The western half of the Tasman Sea is expected to be dominated by a trough this week—with variable winds and some rain, also with northerly winds on its eastern side, good for sailing.

 

Panama to Marquesas

There has recently been a NE blast across Panama and winds/waves are expected to be uncomfortably high for departure until Tuesday, and it may get uncomfortable again from Thursday to Saturday this week. Looking easier next week.

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

 

Port Vallarta to Marquesas

There is a Tejuantepecer blast occurring this week and another expected at the end of March (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

>>>>>>>>>>>>>>>>>>>>>>> 

10 March 2019

Bob Blog 10 March

WEATHERGRAM

YOTREPS

Compiled Sun 10 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.

 

The state of the ENSO = on watch for an El Nino, mixed messages.

ENSO stands for El Nino/Southern Oscillation.    El Nino is the name given when the ocean surface temperatures around the eastern equatorial Pacific rise warmer than normal.  This happens when the trade winds fade. El Nino events, with warmer than normal seas, draw 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.

During February we has an MJO and an extended monsoon trough and that weakened the trade winds and has indeed helped warm the target area for an El Nino.  This can be seen by looking at the latest Sea surface temperature SST anomaly map.  These trade winds have now returned to normal, suggesting that the SST may ease over the next few weeks.

 Sea surface temperatures can be seen at www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html

Of note, there is also a warm stretch from Fiji to French Polynesia and another from Hobart to the central Tasman Sea.

Also of note; the Gulf Stream off the east coast of North America is much warmer than normal.  Overall, the yellow/red outweighs the blue.

 

The Ocean:

NINO3.4 is the parameter which measures the SST anomaly in the target region in the eastern equatorial Pacific Ocean for El Nino or La Nina. This plays with the heat budget of the atmosphere and thus with the weather patterns.

I have gone to the Bureau of Met page for latest NINO 3.4 data at www.bom.gov.au/climate/enso/indices.shtml, and it shows the weekly temperature anomalies since Jan 2015, with a cool period late 2016/early2017, and again in late 2017/early 2018. A warm period started in mid-2018 and briefly reached the El Nino threshold in late 2018, and the dropped and rose in Jan and Feb.  

 

The Atmosphere:

The SOI or Southern Oscillation Index (30 day running mean) comes from the atmosphere and 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.

Over the past year, the SOI has fluctuated up and down.  There was a period of negative SOI back in September/October 2018, but during December/January the SOI went positive, and in February, when the trade winds faded, it went negative. Trade winds have returned to normal , so maybe it will relax during the next few weeks,

 

SOI is seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekly

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

 

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

The International Research Institute of the Climate Prediction Centre compiles data from several ENSO prediction models. Sadly, during this time of the year, around the equinox and the following 6 weeks, the models usually do not perform as well as other times of the year.

The model predictions for the Nino 3.4 SST anomaly is that the seas ae likely to stay the same or slightly cool during the next few months, but some go for a slight increase. Mixed messages.

 

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 HALEH has travelled into the South Ocean, and TC IDAI is in-between Madagascar and Mozambique.

The MJO wave of increased activity is travelling east across the Indian Ocean, and may reach northern Australia over next few weeks encouraging the formation of a monsoon trough, followed by another possible period of Tropical Cyclone formation in the South Pacific late in March.

Rain in the past week has faded in the South Pacific, but intensified across the equator around Papua New Guinea and along the ITCZ in western and central pacific.  See trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

As is usual at this time of the year, as the overhead sun travels from 5S to 3S, a “mirror Convergence Zone” of the ITCZ has formed just south of the equator in the eastern Pacific.

This “mirror CZ” may last for a month or two, affecting those sailing between Galapagos and Marquesas.

   

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is rebuilding over Papua New Guinea and around Fiji, and remains weak elsewhere.

There are some near equatorial westerly winds along the northern coasts of Papua New Guinea and western Solomons, and a Tropical Depression may form between PNG and Solomons by end of this week and drift southwards.

There is a weak convergence zone around southern parts of French Polynesia this week.

 

Subtropical ridge (STR)

HIGH over southern NZ is expected to travel off to northeast.

Next HIGH travelling eastwards across Bass Strait by Wednesday and then around southern NZ on Thursday and then off to the east. 

Next HIGH is likely to travel southeastwards across Tasmania around Sat/Sun.

 

Australia/Tasman Sea / New Zealand

Trough that crossed the North island on Friday developed a Low over Auckland on Saturday and this is expected to travel slowly southwards towards Chathams by mid-week then fade.

Trough from Southern Ocean expected to intensify over Tasman sea on Tuesday then cross South Island on Wednesday and North Island on Thursday followed by a brief southerly flow.

Low is expected to deepen off Sydney on Friday and then go southwards.

 

Panama to Marquesas

There should be good northerly wind for starters around Panama until local Wednesday and then light winds until late next week.  There is a good tail current to north end of Galapagos, then go to 6S 100W, to avoid the building “mirror convergence zone” along around 5 South,

 

Port Vallarta to Marquesas

Winds around Puerto Vallarta are likely to be best for departure around local Tuesday otherwise rather light for starters. 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

>>>>>>>>>>>>>>>>>>>>>>> 

03 March 2019

Bobgram

WEATHERGRAM

YOTREPS

Compiled Sun 3 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 FEBRUARY

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

The eastern equatorial Pacific around Galapagos is the focal region for ENSO and the warm area there seems to have expanded in the past month. The other main change during February is that seas between Japan and Philippines and along the China Sea have become warmer than normal. Also, the South Indian Ocean. The Tasman Sea warm area has weakened a little, and extended to the northeast of NZ. And the Southern Ocean is showing a lot of melt water, which is cooler than normal.

 

To see how the annual weather cycle and the seasons are working out, check the average isobar maps from

www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

The subtropical ridge in the southern hemisphere reaches its annual southern-most position in February and early March. It is stronger than normal from Indian Ocean and across Tasman Sea and to east of NZ.

The tropical South Pacific was affected by a strong MJO and a monsoonal trough, and this shows as low-pressure anomalies.

The low-pressure anomalies around the Arctic is related to the Polar vortex. Note that there is a large anomalous HIGH around the Antarctic.

Zooming into the NZ area, and comparing February with January shows that to north of NZ, the 1010hP (between light blue and dark blue) isobar is in much the same place, but further north the isobars in the tropics significantly lowered during February.

To the south of NZ, the 1010 line has shifted form near 45South to near 50South.

 

The rain during February can be seen at trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html

This shows that during the past month, Vanuatu and Kiribati/Tuvalu were the wettest areas and (after the flooding in late Jan over norther Queensland), Northern Australia to the Philippines was much drier than normal.

 

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 WUTIP reached Cat 5 over open sea, but is now fading and recurving to the north.

TC HALEH has formed over South Indian Ocean,

This indicates that the MJO wave of increased activity is now in the Indian Ocean, and that the South Pacific can expect a relatively quiet time over the next two to three weeks (afte ra month of activity).

 

The weekly rain maps for the past 2 weeks clearly shows the slow path of TC OMA, WUTIP and POLA.

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

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

OMA and POLA have taken a lot of energy/moisture from the SPCZ and it is now weakening at 15 to 20S between Samoa and French Polynesia, and slowly redeveloping between equator and 7 South. The trade winds are back across the South pacific, so it is a good week to do some island hopping (westwards). As good as it gets in March, so if you have been waiting, then this is the week.

 

Subtropical ridge (STR)

HIGH travelling eastwards across North Island on Monday and then to east of NZ

Next HIGH is likely to travel eastwards across Tasmania around Thursday and around southern NZ on Sat/Sun.

 

Australia/Tasman Sea / New Zealand

Trough is expected to travel eastwards across New South Wales on Wednesday and then across Tasman sea. Its front should cross Northland on Saturday.

 

Panama to Marquesas

Light northerly winds for starters around Panama last week, but the forecast is for more useful northerly winds from local Tuesday to Friday. There is a good west-going north of Galapagos.

Then go SE to 5S 100W, to avoid the building “mirror convergence zone” along around 3 south, This CZ grows due to the sun being directly overhead these latitudes at this time of the year (reaches equator on 21st/Equinox)

 

Port Vallarta to Marquesas

There may light winds for starters over next few days, but a good northerly flow is likely for a start around 11 March, perhaps. Weak ITCZ likely between 5N and 2N, and then a “mirror CZ” 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

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

24 February 2019

Bob Blog 24 Feb

WEATHERGRAM

YOTREPS

Compiled Sun 24 Feb 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.

 

A TROPICAL BLAST

I took some snap shots of a cloud feature I spotted last Thursday in the Coral Sea, to the northwest of TC OMA:

It is as if something has triggered a blast from the centre of this cloud feature, causing squall lines to move out to west, south and east in a radial fashion. Fascinating to watch.

I made a video of the event using the one-hour time stepped imagery available from New Caledonia Met site: www.meteo.nc/nouvelle-caledonie/observations/images-satellite

This video is available at tinyurl.com/tropicalblast

 

THE TROPICS

TC OMA moved a little slower than the computer models were picking, and consequently it missed an opportunity to be steered to New Zealand --- however the upper winds did vent a lot of its higher clouds to New Zealand bringing the blessing of some much-needed rain.

TC OMA edged close to southern Queensland from Friday and brought gusty southerly winds.

Gold Coast Airport was gusting over 40 knots on Saturday. Gale winds affected exposed coastal places. OMA has been downgraded now, but may make landfall over New Caledonia as it goes north over next few days, and there are still strong winds and heavy swells long the southeast Queensland coast.

This month the moon was closest it will get this year to earth on Feb 19th (357,012km) and the resulting King tides a few days later, boosted by a strong onshore flow/ storm surge thanks to OMA brought the sea inundating Gold Coast streets.

See www.brisbanetimes.com.au/national/queensland/streets-flood-as-cyclone-oma-approaches-south-east-queensland-20190220-p50z0e.html

 

As mentioned in last week’s blog, TC OMA has triggered a twin cyclone in the northern hemisphere (spurned by the near equatorial westerly winds) This is TC WUTIP and it is expected to strengthen next few days to CAT 4 as it passes to southwest and west of Guam and then to weaken as it travel northwest towards the Philippines.

There is also a tropical depression forming to northwest of Samoa, TD 95P. Its future is uncertain at this stage.

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

The weekly rain maps for the past 2 weeks clearly shows the slow path of TC OMA and TC WUTIP. The South Pacific Convergence zone has had an active week between Samoa and French Polynesia.

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

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The movement of TC OMA to the south has disrupted the monsoonal trough. The SPCZ now stretches from northwest of Samoa to south of French Polynesia. TD 95P is now on the SPCZ and its future uncertain, but if it deepens it is expected to dominant the South Pacific this week and travel south affecting Tonga. The SPCZ is on the northeastern edge of the monsoonal trough, and likely to stretch from Samoa to French Polynesia this week.

 

Subtropical ridge (STR)

HIGH in central Tasman sea on Monday is expected to cross central NZ on Tuesday.

Next HIGH is expected to travel eastwards across Tasmania on Wednesday and then onto northern NZ on Sun 3 March .

 

Australia/Tasman Sea / New Zealand

North of 30S, too much in the way of SE wind for departing east from Australia this week, but may be Ok for going westwards.

Further south it is looking OK for getting east.

 

Panama to Marquesas

There were only light winds around Panama last week, but the forecast is for more useful northerly winds from local Sunday to Wednesday, and then light winds again from Thursday to Sunday.

 

Port Vallarta to Marquesas

There may light winds for a Monday start, and better winds for a start on local Tuesday and Wednesday, then light winds again. Weak ITCZ likely between 5N and 2N, and there may be a “mirror CZ” 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

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

17 February 2019

Bobgram

WEATHERGRAM

YOTREPS

Compiled Sun 17 Feb 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.

 

SEA ROUGHNESS

The Beaufort Scale was developed by the Irish Royal Naval Officer Francis Beaufort in 1805, and first used on HMS Beagle, as an empirical measure that related wind speed to the observed conditions over an ocean (not near a shore).  The story goes that in those days a British Man-of-War could carry 12 sails, which is why the Beaufort scale goes from 1 to 12 (plus 0, for no wind).

 

From the Beaufort Scale, for a given wind speed, the height of the resulting waves offshore for a fully developed sea are given. But the impact of waves on navigation depends on the size of the vessel and factors such as the wave period, the water depth, and swells from other directions. Also, larger waves need time and distance to develop, so the wave fetch is big factor.

 

After World War One, in the 1920s, the first SHIP weather reporting code was being developed, and just one character was set aside to report the “state of the sea” and another for the “state of the swell”. Captain H.P Douglas (later Vice Admiral Sir Percy Douglas and hydrographer of the Royal Navy) devised two ten-point scales to do this.  These scales estimate the roughness of the sea and the swell for navigation.

   The Douglas scale for the “state of the sea” (Wind waves) is as follows:

Degree Height (m)          Height (ft)          Description

0                           no wave                                                         Calm (Glassy)

1                           0–0.10                 0.00–0.33                         Calm (rippled)

2                           0.10–0.50           0.33–1.64                         Smooth

3                           0.50–1.25           1.6–4.1                              Slight

4                           1.25–2.50           4.1–8.2                              Moderate

5                           2.50–4.00           8.2–13.1                            Rough

6                           4.00–6.00           13.1–19.7                         Very rough

7                           6.00–9.00           19.7–29.5                         High

8                           9.00–14.00         29.5–45.9                         Very high

9                           14.00+                 45.9+                                 Phenomenal

Interestingly, It is almost linearly related to the square root of the wave height

 

MetService forecasts give the wind speed to the nearest 5knots. 

MetService uses the following Sea State guide, based on the Douglas and Beaufort Scales,

relating wind speed, sea state and probable wave height:

 

Wins Speed (Knots)        Sea State                           Possible wave height (metres)

0-5                                     Smooth                             <0.5

10-15                                 Slight                                 0.5-1.25

20                                       Moderate                         1.25- 2.5

25-30                                 Rough                                2.5-4

35-40                                 Very rough                       4-6

45-55                                 High                                   6-9

60+                                     Very High                          9+

 

Note that sea state given in the MetService marine forecast is the maximum possible state for that wind speed.  So, if the forecast is for 25 knots, then the seas will be forecast to be rough, but may actually be smooth or slight within places of limited fetch such as the harbour.

For a more detailed discussion on this see the MetService blog at

blog.metservice.com/sea-state-and-swell

When it comes to working out the likely Height H and Period P of swell waves, the main chart used by marine meteorologists is the Bretschneider nomogram (1970) which, based on climatological observations, gives what waves result from a given wind + fetch + duration.    Examples of this are given in that MetService blog.

The Bretschneider normogram does NOT tell us much about the roughness/steepness of swell.

Looking at the cruising forums, there seems to be some agreement that wave Period affects the roughness of the swell

www.cruisersforum.com/forums/f90/wave-height-period-wind-speed-comfort-116480.html

www.cruisersforum.com/forums/f90/how-to-estimate-roughness-of-sea-206263-2.html

In summary, If P in seconds is 1.33 or more times H in feet then waves are manageable.  Any shorter a period and the waves are too rough.  

We use metres, so that translates to if P in seconds is more than a ratio of 4.4 times the H in metres then waves are OK.   I think that perhaps a simple factor of 4 may be a better pick, so a 2m swell is manageable if its period is 8 Seconds or more, and a 3m swell is manageable if its period is 12 seconds or more. However, this is just a rule of thumb that kind-of works for mid-range waves,

I came across an article at widecanvas.weebly.com/nature/waves-height-period-and-length

And here Dr. Dilip Barua offers us a graph which shows 7 roughness or comfort curves and how they sort out with swell given in Significant height in metres and Period in seconds for what he calls “longshore waves” .

Basically, his magenta roughness curve is close enough to acceptable comfort.

 It isn’t a straight line, but at H= 2m height is around P=7 seconds period (ratio of 3.5) and at 3m height it is near 9 seconds (ratio of 3) and at 4m it is at 10 seconds (ratio of 2.5).  The suggestion from this graph is that maybe the ratio between H and P for acceptable waves is not linear, and maybe it drops for the higher waves. I think this relationship requires more research. 

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

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 still a monsoonal trough stretching from the Coral Sea /TC OMA across Fiji to another tropical Low located south of French Polynesia.   TC OMA is expect to slowly drift southwest across NW parts of New Caledonia and then curve southwards into the Tasman Sea.  When it reaches 30S I expect it to encounter stronger WNW winds aloft that may knock off its top clouds and start its spin-down, or perhaps shunt the whole system east-southeast across northern NZ—ah well, we need the rain, and the surfers may get some interesting swells.   The models still haven’t latched onto this system and are offering different scenarios, and at this stage a wide variety of outcomes are still possible, so get updates. 

An interesting meteorological is very likely to soon occur north of OMA. The near-equatorial westerly winds are expected to help spin-up another tropical cyclone north of the equator which will have a life of its own.  This is called “cyclone twinning”, but in this case the spin-up is likely to occur when OMA is near 15S, and usually it occurs when the starter cyclone is a 5 to 10S.

 The weekly rain maps for the past 2 weeks clearly shows this monsoonal trough weakening and the slow path so far of an intensifying TC OMA

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

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is on the northeastern edge of the monsoonal trough ,and likely to stretch from Samoa to French Polynesia this week.

 

Subtropical ridge (STR)

HIGH is travelling east across central NZ next few days and then further east along 40S.

Next HIGH is further south and likely to travel east across Tasmania and into South Tasman sea around Sat/Sun 2/24 Feb

 

Australia/Tasman Sea / New Zealand

Wait until after TC OMA.

 

Panama to Marquesas

Only light winds for starters over next few days, but  a reasonable northerly wind is expected next week, so may as well stay put this week.

 

Port Vallarta to Marquesas

There may be a few days of light winds for starters, and then looks Ok with a departure on Tuesday to Thursday, and then some more light winds until Saturday.  ITCZ likely between 5N and 2N, and there may be a “mirror CZ” 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

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

10 February 2019

Bobgram

WEATHERGRAM

YOTREPS

Compiled Sun 10 Feb 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

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

The monsoonal trough that was over northern Australia earlier this month is now stretching across the Coral sea then in an arc around Vanuatu to north and then east of Fiji.

 

There are tropical depressions spaced out along this monsoonal trough, and there is a good chance that at least one of these may deepen into a tropical cyclone this week, but the models are having problems resolving the details, so it seems best to avoid sailing in this region for the coming week.

 

Sunday evening (Fiji time) weather map shows spaced out depressions, and ex TC NEIL between Fiji and Tonga with gale winds.

The rain map for the past 7 days clearly shows this monsoonal trough,

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

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is draped around a monsoonal trough, and is likely to have at least one tropical low along its length this week. Avoid. The SPCZ the n stretches further to the southeast , touching southern parts of French Polynesia.

 

Subtropical ridge (STR)

Next HIGH is expected to spread from East Australia into Tasman Sea on Monday and then travel east along around 32S fading away to north of NZ on Wednesday.

 

Australia/Tasman Sea / New Zealand

With the Highs crossing central or southern Tasman Sea, the main wind flow north of latitude 35South is from the east, good for sailing from New Caledonia to Queensland.

Easterly winds are expected to get strong and seas rough near Northland from Thursday to Sunday local as a low from the tropics travels southwards to east of NZ.

 

Panama to Marquesas

Same as last week: OK to go any day this week with northerly winds for starters and a good tail current to current to 2N 85W. From there either peel off to the Galapagos Islands or follow the current along around 1deg north to 125W and then head for Marquesas Islands.

 

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

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

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

03 February 2019

Bob Blog 3 Feb

WEATHERGRAM

YOTREPS

Compiled Sun 03 Feb 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.

 

Late January brought some extreme weather, with the peak of a heatwave over Australia, some spots in NZ having a heatwave, an unpresented polar vortex over North America, and the continuing drenching monsoonal low over norther Queensland. A mighty meal for any meteorologist. Sadly, I was out of action, as I needed emergency surgery for a blocked gut.   I’m back home now, so here’s my regular blog once more.

 

REVIEW of JANUARY

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

The eastern equatorial Pacific around Galapagos is the focal region for ENSO and the warm area there seems now to be shrinking. There is also a corridor of warmer-than-normal conditions between Samoa and Southern Cooks — this may add oomph to the South Pacific Convergence zone and act as a possible path for cyclones. The Tasman Sea remains warmer than normal, and ready to add extra rain to any passing lows. And the Southern Ocean is showing a lot of melt water, which is cooler than normal.

The Gulf Stream off the east coast of North America still stands out, which is unusual at this time of the year.

 

To see how the annual weather cycle and the seasons are working out, check the average isobar maps from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

The subtropical ridge in the southern hemisphere is almost at its southern most latitude and the anomalies show it is stronger than normal and maybe somewhat further south than normal.

Zooming into the NZ area, and comparing January with November (December data missing due USA govt shutdown) shows that to north of NZ, the 1010hP  isobar has shifted south from around 10S to 20S.  To south of NZ, the 1010 remains in much the same spot, but the pressure gradient shows stronger westerly winds in the Southern Ocean in January than in November.

 

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

This shows that during January, western South Pacific and Tasman Sea has been dry and it has been French Polynesia that has had the main share of the South Pacific Convergence Zone.

 

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 monsoonal low north of Mt. Isa, and this is expected to stay over land next few days, limiting its chances to develop to a tropical cyclone.

There is a convectively active phase of the MJO over the Western Pacific at present, and it is expected to weaken this week. It may remain in the western Pacific and intensify again by mid-February.  

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is like a monsoonal trough stretching from Australia to Fiji and then as a convergence zone from around Samoa to Tahiti. Tropical lows are likely to form and space themselves along this trough line.

 

Subtropical ridge (STR)

HIGH to east of central NZ on Monday expected to travel off to the east-NE.

New High is expected to travel east across the south Tasman Sea on Tuesday and then around eastern NZ on Thursday and after that to the east-NE.

 

Australia/Tasman Sea / New Zealand

With the Highs crossing the southern Tasman Sea, the main wind flow north of latitude 35 South is from the east, good for sailing from New Caledonia to Queensland.

Easterly winds are expected to get strong and seas rough near Northland from Wednesday in a squash zone with rising pressures to the south and falling pressures to the north.

Further south there are expected to be swinging winds from a passing front on Monday and Tuesday, and increasing NW wind from Friday to Sunday.

 

Panama to Marquesas

Looks OK to go any day this week with northerly winds for starters and a good tail current to current to 2N 85W. From there either peel off to the Galapagos Islands or follow the current along around 1deg north to 125W and then head for Marquesas Islands.

 

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

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 January 2019

Bobgram

No Bobgram this week. I’m indisposed.

Bob McDavitt

20 January 2019

Bob Blog 20 Jan 2019

WEATHERGRAM

YOTREPS

 

Compiled Sun 20 Jan 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 to last week’s blog about barometers is that there is a good website prepared by David Burch at www.startpath.com/barometers that discovers web links to the ten closest barometers near your location and allows you to interpolate between them.

 

The state of the ENSO = on watch for an El Nino, but signs are fading.

The first sign to check when looking at the state of the ENSO index is the sea surface temperature

Latest SST anomaly map shows warmer-than-normal sea all the across the equatorial Pacific. Of note, there is also a warm stretch from Solomon Islands to French Polynesia and another form the Australia Bight to central New Zealand. Also of note; the Gulf Stream off the east coast of North America is much warmer than normal. Overall, the yellow/red outweighs the blue.

Sea surface temperatures across the Pacific on 17 Jan are at www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html

 

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.

 

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 farmonlineweather.com.au 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, show a cool period late 2016/early2017, and again in late 2017/early 2018. A warm period started in mid-2018 and briefly reached the El Nino threshold in late 2018, but is now fading.

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

 

The Atmosphere:

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.

Over the past year, the SOI has fluctuated up and down. There was a period of negative SOI back in September/October 2018, but during December the SOI went positive, indicating that atmospheric pattern is out-of-sequence with the oceanic pattern.

Uncoupled conditions is 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)

 

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

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 ae likely to stay the same or slightly cool during the next few months, so that there is a decreasing chance of an El Nino event.

The performance of these statistical and dynamical models since 2017 may be seen from the IRI website and shows an interesting amount of variation.

 

 

THE TROPICS LAST WEEK

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

There are two tropical depressions around at present: 01W over the Philippines and 10S between Madagascar and Mozambique.

Models now have the idea of a developing tropical lows off the northwest and northeast of Australia later this week.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is active from Norther Australia to Solomon Islands and then stretches across the South Pacific almost all the way to Tahiti. A low is likely to form to south of Rarotonga after wed UTC and take some of the convective energy from the SPCZ southwards to higher latitudes.

 

Subtropical ridge (STR)

HIGH crossing Tasmania tonight is expected to travel slowly NE across the Tasman Sea by Wednesday UTC, and then fade as a ridge along 30S during Thursday UTC.

Next HIGH is expected to travel east along 45S past Tasmania on Wednesday UTC and then across central/northern NZ by the end of the week.

 

Australia/Tasman Sea / New Zealand

With the Highs crossing the Tasman Sea, the main wind flow north of latitude 35South is from the east, good for sailing from New Caledonia to Queensland. Any vessels wishing to get from Australia to NZ can possibly motor thru the High near 35 south or sail in disturbed westerly winds and sometimes large swells further south.

Arrange arrival in New Zealand between fronts. One front is expected to reach NZ on local Monday, another on local Wednesday/Thursday, and the next on local Saturday/Sunday.

 

Panama to Marquesas

Looks OK to go any day this week with northerly winds for starters and a good SW going current to 2N 85W. From there either peel off to the Galapagos Islands or follow the equatorial current to 120W and then head for Marquesas Islands.

 

King Tides

Note that there is full moon tonight (and a total lunar eclipse visible from North and South America. This month’s lunar perigee (moon closest to Earth) is Monday 21 Jan 1959hr UTC, so there are some King Tides later this week (more extreme high and low tides). Take this into account in your travels.

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

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

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

13 January 2019

Bob blog 13 Jan 2019

WEATHERGRAM

YOTREPS

Compiled Sun 13 Jan 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.

 

HOW TO READ A BAROMETER

That barometer you got last Christmas can be put to use as a weather forecaster.

OK, all it does is read air pressure, or the weight per unit area of the column of air above it. But by following these readings you can tune into the vibrations of the weather pattern as it changes. Like whiskers on a cat.

 

Pressure. Why is it so important? Because imbalances in air pressure cause wind and weather. You want to know about wind and rain, but weather forecasters talk about isobars and fronts. This is because isobars and fronts have a pattern that is easier to draw and follow. Isobars are those lines on a weather map joining together places with the same surface pressure. The shape of the isobars describes the weather pattern, so changes in the weather can be forecast by tracking the changing isobar pattern or by observing pressure change.

 

Pascals.  Most barometers measure pressure in hectoPascals (hPa). These are the same as what used to be called millibars. A hectoPascal is one hundred Pascals, and a Pascal is the standard metric unit for pressure, named to recall an experiment done under the direction of Blaise Pascal in September 1648 that used a barometer to show how pressure changed with height. This experiment was historically important for it showed the limitations of Aristotelian philosophy and showed how thinking and experimenting (science) can win out over simply modifying an explanation (literature/journalism)  (see www.strange-loops.com/scibarometer.html). Truth vs struth.

Other common pressure units are inches and millimetres of mercury. They refer to the height of a column of mercury which can be supported by the air pressure. To convert a pressure reading from hectoPascals to inches divide the hectoPascals by 33.86. And to convert from hectoPascals to millimetres multiply the hectoPascals by 0.75.

 

Types: Your barometer is most likely an aneroid (= without fluid) or digital (using a pressure transducer) type.

Aneroid Barometers: Inside there is a metal cell only partially filled with air. The size of this airtight cell varies with changes in the surrounding air pressure, and these variations are passed on to an indicator needle by a series of levers. It is all mechanical, so no batteries are needed. If the metal chamber cracks then the barometer will no longer work.

These barometers usually have words such as “Stormy” for low pressures (980 to 1000 hPa) and “Dry” for high pressures (1020 to1030 hPa). These words are at best only a first guide to the weather and date back to Vice-Admiral (Royal Navy) Robert Fitzroy (1805-65) who first visited New Zealand with Charles Darwin on the Beagle in 1835. Fitzroy later became New Zealand’s second Governor (in 1845) and Superintendent of the British Meteorological Department (in 1853).

Digital Barometers: Digital barometers have the advantage that they can display a graph of recent pressure change and the disadvantage that they require batteries. They may give a read out to the nearest tenth of hectoPascal (precision), but their accuracy is usually to around a one hectoPascal, so don’t bother paying more for this feature. Some use the pressure (and temperature) reading to produce an image that forecasts the weather for the next day or so. For a yacht, a digital barometer is better than an aneroid barometer so long as it has a display of recent pressure change.

 

Will it rain? It is OK to tap the outer glass of an aneroid barometer (just enough to see a change). By so doing you shift any recent pressure change stored in the mechanical linkage to the measuring needle. The resulting slight movement indicates whether the pressure is rising, steady, or falling. If the measuring needle goes to the left then there has been a drop in pressure recently. Most digital barometers also indicate if the pressure is rising or falling.

 

What causes pressure to fall?

Several things can cause this.

• maybe there is an approaching low pressure system (marked as an L on a weather map).

• maybe the air is getting warmer (and less dense)

• maybe there has been an increase in the moisture or cloudiness in the air (YES- damp air weighs less than dry air)

Cricketers know that a  passing cloud increases humidity and reduces air pressure allowing the cricket ball to spin better.  Watch a spinner bowler wait for a passing cloud next time you see a game of cricket, sure to be an “out!”.

• maybe there has been a decrease in the amount of air above (this happens when rising air is removed by strong winds aloft faster than it can be replaced. increasing the speed of the rising air).

• maybe it is just the time of the day. There is a twice-daily roller coaster.

There is a twice daily roller coaster of pressure due to a solar-induced atmospheric tide and called the “diurnal pressure change”. Pressure rises between about 5 to 9 local am or pm and falls between 11 and 3  local am or pm.  Daylight saving alters this.

The amount of this diurnal change is more in the tropics (about 3 hPa per tide) than over New Zealand (about 1 hPa). The easiest way to remove diurnal change from your calculations is to read your barometer at the SAME TIME of the day, preferably with the “flat tops” at about 10am (and maybe at 10pm).

 

As a rule of thumb,

a sustained DROP in pressure is a sign of more chance of rain

a sustained RISE in pressure is a sign of less chance of rain

 

Where to put it?

Anywhere that is most convenient. But when deciding where to put your barometer there are places that you should avoid..

• Avoid placing a barometer in draughty places such as near a door. In such places the air pressure is too variable.

• Avoid direct sunlight on a barometer. This will warm and expand the metal cell causing a false recording of falling pressure. For the same reason, do NOT position your barometer near a heater.

• Avoid placing a barometer in a well-sealed or air-conditioned room. Such places do not respond well to changes in pressure.

SO whether in your house or an your yacht, the best place is on an interior wall.

 

Setting a Barometer.

The main use for a barometer is not so much to read pressure, but to measure CHANGES in pressure over time. Digital barometers usually display this as an arrow or as a bar graph. In an aneroid barometer there are normally two needles. The needle connected to the insides of the barometer is called the measuring hand. The second needle is a movable pointer (sometimes called the setting hand) which is free to be moved around by means of twirling a knob at the centre of the glass. When you arrange it so the setting hand is directly over the measuring hand you have set your barometer. The idea is that you set your barometer early in the day. Then, later, you need only glance at your barometer to see how far the measuring hand has moved. If it has moved to the left (of the setting hand) then pressures are falling.

If the pressure is changing rapidly this suggests that an approaching weather system is moving quickly or becoming more intense. In this case isobars are moving quickly across your area and are possibly getting closer together. This usually results in strong winds, and can be taken as a STRONG WIND WARNING. But sometimes the isobars in your area may not change position much even though they are getting closer together, in which case you may have stronger winds and only a small pressure change.

 

Getting it adjusted (calibrated).

This only needs to be done if you want to compare your readings with others or with the weather map. To do this, adjust your barometer so that it reads Mean Sea Level (MSL) pressure. Mean Sea Level is the standard datum level to which all barometers should be adjusted. This adjustment will automatically apply a correction to your barometer that takes into account its height above sea level. Pressure near the ground drops off at the rate of about 3hPa per 25 metres of altitude. SO if you change the altitude of your barometer by more than 5m , then  re-calibrate it.

Calibrating your barometer is easy. All you have to do, once you position your barometer in a new location, is look for the latest MSL pressure at a location near you (on the Internet or ask Siri or Alexia or Google). Then tweak your barometer to read this value. For aneroid barometers there is normally an adjustment screw found at the back of the barometer.  For digital barometers this usually means pressing the menu or settings button. Try to do this adjustment at a time when the pressure is not changing much and is neither very high nor very low  (around 1010-1020 hPa)  with no fronts coming, and around 10am local (a flat top).

Your barometer may slowly drift out of adjustment, especially after a bumpy voyage on a yacht, so check it every six months or so.

 

THE TROPICS LAST WEEK

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

Much quieter now that the recent MJO of extra convection has moved off from the central Pacific. Last week PENNY and MONA faded. There is still a depression near Micronesia,01W ONE, but this is not expected to develop.

GFS model has the idea of a developing tropical low to southwest of Bali by the end of this week, but ECMWF has a weaker feature.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is active from Solomons to Tuvalu to Tokelau/Samoa then southeast to Southern Cooks. There may be a tropical low over Fiji by Thursday UTC moving across Tonga on Friday UTC and south of Niue on Saturday UTC.

 

Subtropical ridge (STR)

HIGH that has been east of NZ is expected to travel eastwards along 36 to 38S.

HIGH over Tasmania today is expected to travel slowly NE across the Tasman Sea this week.

 

Tasman Sea / New Zealand

The main event of this week is the front that is expected to travel across the North Island on Monday, turning into a cut off /slow-moving low to east of the North Island for the remainder of the week. This system has cold air above it, so that may bring thunder and hail to the North Island on Monday, a change from the settled weather since Christmas.

After this trough of Monday the wind over the eastern Tasman Sea and NZ for the remainder of the week ahead is likely to be southerly and showery. May be a week to stay put in NZ.

 

Australia/ New Caledonia:

With High pressures in the Tasman Sea and low pressures in the Coral Sea this week, the winds favors one-way traffic form Noumea to (southern) Queensland, but winds over 20 knots and swells over 2m at times.

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

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

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

06 January 2019

Bob Blog 6 Jan 2019

WEATHERGRAM

YOTREPS

Compiled Sun 06 Jan  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.

 

To start the New year off, here's  a review of the stats for downloads of the illustrated edition of my weathergram: (/metbob.wordpress.com)

2018 plateaued (with a slight increase) at over 11,000 view and over 7,000 unique visitors, with around 30 likes and 30 comments.   This is sufficient for me to see a worthwhileness so that I'll continue in weathergrams (which started around 1998). I'm not sure if I've broken any seniority records yet with my blogs – let me know if you think so 😊.

My weathergram also is made available to saildocs-- To get a one-off weathergram via email: 

Send an email to query@saildocs.com,  no subject needed with message SEND nz.wgrm

There is also an archive with a language translator at weathergram.blogspot.com.

TEXT only edition has been sent out in 2018 via Mailchimp to over 600 email addresses, but I've also started text-only-weathergrams via Cruisersat.net which also offers , for satellite phones,  a trimmed down to 4-TXT messages edition  (wow).

I may slowly ask people to shift from mailchimp to cruisersat during the next year.  Not sure yet.

 

To subscribe 

a) to my text-only weathergram, send an email, no subject needed,  from  your vessel's email address  to weathergram@cruisersat.net,  with the message SUBSCRIBE Boat name

or b)  or shortened weathergram for sat phone in four  SMS text messages, send an email,  no subject needed, from  your vessel's email address  to weathergram_short@cruisersat.net,  with the message SUBSCRIBE Boat name

 

REVIEW of DECEMBER

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

(parts of US govt are shut down again so unavailable for direct data).

The eastern equatorial Pacific around Galapagos is the focal region for ENSO and is still only slightly warmer than normal.

 The main warm anomaly is now over the Tasman Sea.

There is also a corridor of warmer-than-normal conditions between Tuvalu and French Polynesia— this may add oomph to the South pacific Convergence zone and act as a possible path for cyclones .

The Gulf Stream off the east coast of North America still stands out, which is unusual at this time of the year. 

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

The rain map shows extra convergence over northern Australia to equator/180 and from Tuvalu to Niue, also a drier-than-normal zone between Tokelau and French Polynesia (this zone may well change is the sea surface temperature anomalies are indicative).

 

THE TROPICS  LAST WEEK

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

PENNY was downgraded today but is still heading for northeast Queensland and may redevelop before making landfall.

MONA is category one and after doing a clockwise loop earlier today is expected to curve SE/S across eastern Fiji during tonight and Monday then move off to the southwest.  Also bring lots of rain.

During the past week Tropical Storm PABUK  brought record-breaking rain to Thailand (during their "dry" season).

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is active from Tuvalu to eastern Fiji and is likely to be active from Niue to Austral Islands this week.  MONA is expected to weaken and travel to SW once it has visited the  Lau group, and PENNY is expected to redevelop and make landfall  over NE Queensland around Thursday.

 

Subtropical ridge (STR)

A new HIGH is expected to travel eastwards from Tasman Sea across New Zealand on Tuesday/Wednesday and then to east of NZ along 40S.

Another HIGH is likely to form off Tasmania on Thursday and travel over Southern NZ on Sat/Sun 12/13 Jan.

 

Tasman Sea / New Zealand

Troughs are expected to cross southern and central NZ on Monday and Thursday.

 

Australia to New Caledonia:

With High pressures in the Tasman Sea and low pressures in the Coral Sea this week, the winds favors one-way traffic form Noumea to (southern) Queensland.

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

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

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

Blog Archive