Translator

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

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