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 27 Sep 2020

 

CAPE or Convective Available Potential energy, is the integrated (total) amount of work that the upward (positive) buoyancy force would perform on a given mass of air (called an air parcel) if it rose vertically through the entire atmosphere. Positive CAPE will cause the air parcel to rise and is an indicator of atmospheric instability in any given atmospheric sounding, while negative CAPE will cause the air parcel to sink.

 

Instability and rising motion in a cloud can cause a thunderstorm, CAPE values over 5Kj/Kg are significant in creating thunderstorms. This means that CAPE can be used as an indicator of the intensity of the South Pacific Convergence Zone. So I’m adding the mid-week CAPE map (from predictwind.com) to my illustrated edition of weathergram, as it shows another rview of the SPCZ..

 

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

Just two tropical depressions today. 15W and 14W (ex DOLPHIN at 40N 146E)

Also, some high potential for development off west Mexico coast., near Philippines, an d in the N NE Atlantic, off Africa

 

SPCZ=South Pacific Convergence zone.

SPCZ is moderate and in its normal position, from Solomon Islands to Samoa. The CAPE map also shows some convection along 15S.

Passing trough over Fiji /Tonga on Wednesday, and Southern Cooks on local Tuesday/Wednesday and Southern Cooks on Thursday.

Accumulated rainfall for next week from windyty.com

 

SubSubtropical  Ridge

HIGH 1024hPa over New South Wale on Tuesday and broaden as it crosses Tasman Sea , reaching North Island on Thursday and Friday, leaving a lingering ridge over North Island.

 

Tasman troughs

Low 966 hPa south of NZ moving south and deepening to below 050 hPa at 55S on Monday, then moving east., followed by vigorous S flow over NZ until Wed with huge swells. .

Front over South Island on Friday with NW winds followed by westerly winds.

 

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

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's Blog 20 May

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 20 Sep 2020

 

LA Nina update

The main Met sites have confirmed that in the past week we have indeed started a new La Nina episode. It is expected to be a weak one, peaking around December and fading by March 2021. Should have a moderating effect on the number of cyclones, with the main ones forming WEST of 180.

 

Spring equinox and Daylight saving

The equinox is at 0130UTC on 22 September.

NZ switches to daylight time at 2am Sunday 27 Sep

In Australia Daylight saving is observed in New South Wales, Victoria, South Australia , Tasmania. Australia Capital Territory, and Norfolk Island

It starts on 2am on first Sunday of October.

Fiji starts 2am 8 Nov

French Polynesia doesn’t have daylight savings

Tonga is no longer (since 2017) having Daylight saving

 

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

Three Cyclones in the North Atlantic, TEDDY and WILFRED (+ Paulette’s remains north of 30 north, not shown ). But during the past week there were up to 7 systems worth watching. BETA in Gulf of Mexico--- so we have switched to the Greek Alphabet for names. NOUL is near Bangladesh. Also a high potential for development off west Mexico coast. And a rare ‘Medicane’ in Greece in the Mediterranean Sea with at least two fatalities, see https://www.bbc.com/news/world-europe-54219180

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is moderate and slightly north of normal from Solomon Islands to North of Vanuatu to Tuvalu /Samoa.

Passing trough over Southern Cooks on local Tuesday/Wednesday.

 

Subtropical ridge (STR)

HIGH 1028hPa over NZ moving east along 40S, but leaves a lingering ridge over North Island on Monday that may allow a new HIGH 1020pa to travel east along 30S to E of NZ from Tues to Sat.

 

Tasman troughs

Passing trough over NZ on Tuesday.

Low forming east of Tasmania on Thursday and crossing southern NZ on Friday at around 995hPa.

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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

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 13 Sep 2020

 

LA Nina watch

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

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.

There has been a positive trend I the SOI over the last few weeks , heading for the start of a La Nina event soon.

The SOI 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 showing a cooling (La Nina) trend . It looks like the Atmosphere and Ocean parameters are “coupled” or doing much the same thing, so a La Nina event may indeed soon be occurring.

Sea temperature anomaly, taken from

www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

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 a 55% chance of weak La Nina for Sep Oct Nov. This is the trend of the average of the models.

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

 

So, we are currently “neutral”, but we are on watch for La Nina trends.

 

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

Three Cyclones in the North Atlantic, PAULETTE, TD20 , and RENE,

and one inn Gulf of Mexico, SALLY. Also a high potential for development off west Mexico coast.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is moderate and slightly north of normal from Solomon Islands to North Vanuatu to Tuvalu /Samoa. Passing trough over Southern Cooks on local Sunday/Monday.

 

Subtropical ridge (STR)

HIGH 1028 to 1030 hPa crossing Tasman Sea Tues/Wed an d the travelling along 32S between Fiji an d NZ on Wed night/ Thursday, with a squash zone of rough weather over Fiji, easing from Friday.

Next High is expected to cross Tasmania on Friday and grow to 1032hPa in South Tasman on Friday/Saturday, crossing central NZ during the weekend.

 

Tasman troughs

Strengthening NW flow south of 40S on Monday, followed by a cold front on Tuesday with heavy rain for Southern Alps, then another front for all NZ on Thurs night/Friday.

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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 6 Sep

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 6  Sep 2020

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REVIEW OF THE LAST MONTH (August 2020)

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

A noticeable cooling of SST along eastern Pacific Equatorial zone, A sign that we are likely to have a La Nina. Soon, and this tends to bring the southern hemisphere’s subtropical ridge southwards, especially in the South Pacific.

The North pacific and Atlantic have warmed between 30 and 50N but this may be seasonal.

 

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

The monsoon is much like last month. The northern hemisphere sub-tropical ridge has weekend and the southern hemisphere subtropical ridge is in much the same place, has shrunk a little, but for the High near western South America has intensified.

 

Zooming into the NZ area, and comparing monthly anomalies from last month with now, shows that the sub-tropical ridge has shifted north over NZ (as per a normal July), but strangely has intensified over Australia.

The 1015 line over NZ has shifted north, allowing more fronts to spread north over NZ.

The 1025 over Australia has weakened but the High near the Andes has intensified.

The Antarctic high has also intensified.

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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

MAYSAK last week affected Japan and South Korea and sunk a cattle ship .

HAISHEN follows , possibly stronger.

JULIO is moving offshore from west Mexico.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is moderate and in two bits, one from Solomon islands to Vanuatu to south of Fiji, t’other over Tuvalu to Samoa, briefly Tonga.

Passing trough over Fiji/Tonga mid-week, turning into a Low that goes Southeast.

 

Subtropical ridge (STR)

HIGH 1034hPa in Tasma Sea Monday travels onto central NZ 1028hPa on Tue/Wed then goes off to east.

Next HIGH expected to cross Tasmania on Thu 1032hPa , then ENE to Northern NZ 1022hPa by Sunday.

 

Tasman troughs

Trough is crossing NZ North Island tonight.

Next Tasman trough is expected to reach NZ South Island on Wednesday, lingering on Thu and developing into a Low over northern NZ on Friday, moving off to east on Sat.

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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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