Bob Blog

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.

 

Compiled Sun 26 July 2020

 

Addendum to last week’s blog about barometer. There is a weather map on the web that shows the 1013.25 hPa . This shows how straight it is, dividing the places of higher pressure and lower pressure evenly. The map also has pink areas for rising pressure and blue areas for lower pressure, which you can check with your own barometer. It’s

www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=1000000000&CONT=aupa&MODELL=gfs&MODELLTYP=1&BASE=-&VAR=slpd&HH=6&ZOOM=1&ARCHIV=0&RES=0&PANEL=0&LOOP=0&INFO=0&WMO=

 

New Cyclone model.

A new tropical cyclone forecasting model has the potential to save lives here and in the Pacific.

 

More time for communities to prepare is key, and the new outlook model will generate predictions for the number of tropical cyclones at an individual country level, up to four months before the start of the tropical cyclone season.

 

It has been developed by climate scientists from the University of Newcastle and the National Institute of Water and Atmospheric Research (NIWA), in New Zealand.

 

The new cyclone outlook model can detect increased cyclone activity and forecast cyclone activity months ahead of time, he said.

 

It’s also known that climate change will intensify the impact of cyclone seasons, and is making the events more and more common. However, at this stage, the Nov 2020 to May 2021 cyclone season is expected to be about to BELOW normal.

 

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The Tropics

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

There are THREE active storms at present, HANNA is attacking inland Texas, DOUGLAS is brushing by Hawaii, and GONZALO is skirting the north coast of South America. There are several areas around or increased potential for cyclone development.

 

WEATHER ZONES

Weather Zones (see text) as expected Wednesday 00UTC showing isobars, winds, waves(magenta), Rain (Blue), CAPE (pink), STR, and SPCZ.) 

 

SPCZ=South Pacific Convergence zone.

This is likely to be about normal from Solomon Islands to north of Vanuatu to Tuvalu and Tokelau to Samoa an d then SE to French Polynesia

Passing trough - now near Cook Islands, moving onto French Polynesia mid-week

Next passing trough over New Caledonia on Wed/Thurs.

 

Subtropical ridge (STR)

HIGH 1030-1034hPa in central Tasman crossing central NZ on Mon and the traveling off to southeast from Tuesday but leaving behind stubborn ridge. There is expected to be a SQUASH zone on the northern side of this high, peaking with strong to possible gale ( in exposed places) SE winds near Tonga mainly Tues/wed.

New high 1028hPa expected in west central Tasman on Friday.

 

Troughs

Forget about crossing the Tasman Sea this week. A Low, forming off Coffs tonight is expected to go SOUTH and deepen to 986hPa off Sydney on Tuesday then SE to South Tasman by wed/Thu .

Another Low is expected to from north of first low in central Tasman Sea on wed and move SSE into South Tasman 994hPa for southern NZ by Friday

 

From Panama: ITCZ 10N to 7N, light winds maybe NW for starters but SW form 8S to 88W then S or light winds a round gala then a switch to S winds. Not sure what GANZALO will do.

 

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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

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Bob Blog 19 July

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.

Compiled Sun 19 July 2020

 

Your 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.

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)

Cricket players know that a passing cloud increases humidity and reduces air pressure allowing the cricket ball to spin better. Watch a spinner bowler watch for a passing cloud next time you watch a game of cricket, may well lead to 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 as shown here from windy.com, looking 9 days of pressure changes at Cairns (early January 2019)

 

This is 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 maybe10pm).

 

Note that the average atmospheric pressure is 1013.25hpa, and the closest isobar to that is 1012. It turns out that 1012hpa (mostly) divides the higher pressures (drier, more settled weather) from the lower pressure s (unsettled weather). It was labeled as the change area on the old-time barometers. It is a useful tool for weather forecasting.

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The Tropics

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

There are currently NO active tropical storms. There are, however, several potential areas for propagation.

WEATHER ZONES

Weather Zones (see text) as expected Wednesday 00UTC showing isobars, winds, waves(magenta), Rain (Blue), CAPE (pink), STR, and SPCZ.)

 

SPCZ=South Pacific Convergence zone.

This is likely to be nudged to the north a little this week and just be from Solomon island d to north of Vanuatu. due to the STR being knocked north over much of the South Pacific by Lows over NZ.

However, there are likely to be passing troughs over Fiji and Tonga /Niue on Monday/Tuesday ,and another passing trough Se of French Polynesia.

 

Accumulated rainfall for next week from windyty.com

Subtropical ridge (STR)

HIGH 1026hPa should move into central Tasman near 35S on Friday and over northern NZ for the weekend.

The record-breaking rain over Northland from a Low in the NW Tasman is now clearing as the Low goes NE then SW (as a new low) south of Fiji on Monday.

Band  of rain crossing NZ on Tuesday.  Another Low, 986hPa, south of NZ is expected to travel NE along east coast on Tue-Wed, bringing strong SW and rough seas onto the North island west coast.

Winds around Northland should start easing again on Wednesday but THURSDAY is looking to be the day this week for departing North.

From Panama: Not as squally as last week as ITCZ may ease a bit. 10 to 15kt west to SW winds as far as 90W. Further west, the winds swing slowly to S then SE. Tropical features may form off west of central America, but not a bother on voyage to Marquesas.

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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

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Bob Blog

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.

Compiled Sun 12 July 2020

 

ENSO (El Nino /Southern Oscillation) update

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 strengthens the trade winds, and the El Nino, with warmer than normal seas, draws the subtropical ridge closer to the equator, weakening the trade winds. 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 Atmosphere:

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 a brief El Nino late in 2019 the ENSO has been roller coasting above and below zero, in a neutral away . Recently, the subtropical ridge in the southern hemisphere has been remaining in the same position, slightly south of normal.

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

The Ocean:

The sea surface temperatures in the equatorial eastern Pacific has been is now showing a cooling (La Nina) trend. It has recently stalled , but climate models show this stall is likely to be temporary

For Sea temperature see www.ssec.wisc.edu/data/sst/

This image shows the Humboldt current moving onto the Galapagos, cooling the sea.

Waters just beneath the surface are slightly cooler than normal. These trends are towards a La Nina.

The International Research Institute of the Climate Prediction Centre compiles data from several ENSO prediction models.

The model forecasts shows ~45% near-equal chance of La Nina or neutral over next few months, with a slightly more chance of La Nina from Sep to Jan then neutral. It may be a weak La Nina.

 

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

So the outlook is for a near Neutral window, but we on watch for La Nina trends.

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The Tropics

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

CHRISTINA is traveling west in the north Pacific but should fade before reaching Hawaiian longitudes. However, it is likely to be followed by another cyclone during the next week.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is active around Solomon Island, over northern Vanuatu, and Tuvalu/Tokelau/Samoa with a trailing trough further SE.

 A brief trough should cross New Caledonia to Fiji slowly from Tuesday to Saturday.

 

Subtropical ridge (STR)

HIGH 1026hPa over northern NZ moving off to east along 40-45S,

Next HIGH 1034hPa expected south of Tasmania by Tuesday to get south of NZ as 1028hPa by Thursday the go NE and rise to 1030hPa. It also should leave a ridge back into Tasman Sea for a few days 1024hPa to 1018hPA.

Active trough in Tasman sea to cross northern NZ around Wed followed by a Low until Sunday then SE/S winds.

 

From Panama: Squally due to ITCZ, but often light winds. 10 to 15kt W to SW winds from 80W to 90W. then southerly winds to 95W, then SE winds. Tropical features likely to form off west of central America, but not a bother on voyage to Marquesas.

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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

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

 

Bob Blog 5 July 2020

 

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.

Compiled Sun 5 July 2020

REVIEW OF THE LAST MONTH (June 2020)

Sea Surface temperature anomalies as at start of May can be seen at https://www.weatherzone.com.au/climate/indicator_sst.jsp?lt=global&lc=global&c=ssta

Early July (below)

Looking at the SST during the past few months we now see a weakening warm pool in the Indian Ocean/Tasman Sea/Fiji. This means there may be a NEGATIVE Indian Ocean Dipole is possible later this year over Australia with above-average winter/spring rainfall over parts of Southern Australia, perhaps—3 out of six models say a sort of yes.

According to BoM (Australia) that cooling sea in eastern equatorial Pacific is significant. ENSO (El Nino/southern Oscillation) is likely (around 50%) to bring a La Nina late winter or early spring.

La Nina tends to bring the subtropical ridge southwards.

SAM (Southern Annular Mode) is currently positive for a few weeks., keeping southerly outbreaks away.

To see how the annual weather cycle and the seasons are working out, we can 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

Last month , there was a belt of low pressure near 40-50S from south of South Africa to the east of N and has gone south to 50-60S allowing the sub-tropical ridge to get as far as 50S, rather strange for winter.

Zooming into the NZ area, and comparing monthly anomalies from last month with now, shows that the subtropical ridge STR has strengthened

The 1020 line has shifted north a little in the Tasman Sea, allowing more fronts to get further north over NZ.

The Tropics

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

Tropical Depression 5 in the Atlantic is expected to move offshore. There are a few moderate patches of potential development especially west of central America, but these are not really expected to come to much. But stay wary.

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is active around Solomon Island, over northern Vanuatu, and Tuvalu/Tokelau/Samoa.

 A tropical trough should cross Fiji/Tonga on local Wednesday and Southern Cooks onlocal Thursday. and then go southeast.

 

Subtropical ridge (STR)

HIGH 1024-1026 to east of NZ moving off along 40-45S,

Next HIGH 1028 expects to cross Tasmania on Tuesday/Wednesday and then northeast across Tasma Sea onto on northern NZ on Friday/Sat/Sun.

Active front crossing North Island tonight/Monday. Another front/Low visits South Island on Tuesday followed by strong SW winds on Wednesday. Big swells in eastern Tasman Sea on Tuesday and Wednesday.

From Panama: Squally due to ITCZ, but some rare NW winds are likely around Panama this Monday/Tuesday followed by light winds for starters. Will need to go south at first and maybe then NW to handle SW winds SW winds as far as 90W. Some tropical features likely to form off west of central America, but not a bother on voyage to Marquesas.

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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