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

29 December 2019

Bob Blog 29

 

Bob Blog 29 Dec 2019

WEATHERGRAM

YOTREPS

 

Compiled Sun 29 Dec 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.

 

On Friday 27 Dec tropical cyclone SARAI went south past the west of Fiji

 

Using windy.com we can view the temperature/rain/wind and barometric pressure at the Nadi Airport observing station, showing the rise and fall and rise again of the wind as SARAI passed by. Peak gust 58 knots. (See illustrated edition). .

 

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The Tropics

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

 

TC PANFONE brought destruction to Philippines early last week

TC SARAI is currently heading for Nuku’alofa in Tonga but may swing left and go northeast.

There is high potential for TC formation between Guam and Palau this week

 

WATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is mainly located from TC SARAI to Samoa to Southern Cooks his week.

So, it’s not a week for sailing around the South Pacific.

 

Subtropical ridge (STR)

HIGH in the central to north Tasman Sea is blocked this week and will be reinforced by a new High over the south Tasman sea on Friday.

 

Tasman Sea /NZ/Aus

Some deep lows are expected east of NZ this week , blocking a High is the Tasman Sea and maintaining a SW flow over NZ.

These SW/S winds may often reach to 25S this week. Better to get to NZ next week.

 

For Noumea to Aus: With a blocked High in the Tasman sea, should be OK with SE winds for this route this week .

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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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22 December 2019

Bob Blog 22 Dec

WEATHERGRAM

YOTREPS

Compiled Sun 22 Dec 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.

On the 19th Dec, Australia has its hottest day for a second straight day as area face ‘catastrophic” fire conditions

See www.washingtonpost.com/weather/2019/12/19/australia-has-its-hottest-day-second-straight-day-areas-face-catastrophic-fire-conditions/

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The Tropics

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

 TC PANFONE is at 999hPa traveling west-northwest just to north of Palau, towards Philippines

There is high potential for cyclone formation to NW of Fiji this week.

 

SPCZ=South Pacific Convergence zone.

The SPCZ is situated from PNG to Samoa and then fades off to the SE.

It is activating this week and expected to form tropical lows NW of Samoa and north of Fiji.

One of these is likely to deepen into a cycle by Friday and has 50% chance (1 model out of 2) to move to the Fiji area by the weekend.

SPCZ stretches into a trough /convergence zone over the Niue to Tahiti area,

So, it’s not a week for sailing around the South Pacific.

 

Subtropical ridge (STR)

HIGH in the south Tasman Sea on Monday should stay there this week and send smaller Highs across the South Island and central NZ on Wednesday and again next Monday.

Tasman Sea /NZ/Aus

Low to NE of North Island on Monday expected to go off to SE by end of Tuesday.

Trough expected to travel NE across the country on Thursday and Friday followed by a SW flow.

Outlook for next week is for High to stay put feeding more troughs and SW winds to NZ.

 

For Noumea to Aus: With a blocked High in the Tasman sea, should be OK with SE winds for this route this week .

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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

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

 

15 December 2019

Bob Blog 15Dec

WEATHERGRAM

YOTREPS

Compiled Sun 15 Dec 2019

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

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

-=-=-=-=-=

The Tropics

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

There are no active cyclones around at present.

There is potential for cyclone formation showing in Micronesia stretching to south of Philippines.

 

WATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to be active all the way across the South Pacific this week from PNG across northern Vanuatu to Fiji, and from Samoa to middle part of French Polynesia. Maybe better to sit back and relax rather than island hopping.

The trend is for this to become more unsettled next week

Passing trough across Samoa on Wed/Thu weakening further east.

 

Subtropical ridge (STR)

HIGH that has been blocking to east of NZ is expected to move off on Wednesday UTC.

Next HIGH is expected to form in the Tasman sea on Tuesday local and gets knocked off to the Ne and fade by Thursday.

Another HIGH may then form in the Tasman by Friday local and then visit northern NZ on Saturday.

Tasman Sea /NZ/Aus

Main feature this week is a 994hpa low expected to cross central NZ on Tuesday local with large swells in the Tasman. followed by a SW flow on Wednesday, and a trough on Friday.

Outlook for next week is more SW flow and a possible low 1007 for Northland on Boxing day. followed by more SW flow. Not a good week to arrive in Northland from the tropics, or to get south for the “summer”.

For Noumea to Aus: A trough and southerly wind change in Noumea on Monday and Tuesday the looks OK.

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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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08 December 2019

Bob Blog 8 Dec

WEATHERGRAM

YOTREPS

 

Compiled Sun 08 Dec 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 THE LAST WEEK

 

A series of fronts with heavy rain and strong winds battered South and central NZ in the past week. The main cause of this “river of wind” has been the squash zone between and quasi-stationary HIGH east of NZ and a very deep (at times below 960 hPa) Low caught in an upper low so that it looped as shown in the illustrated edition for Sat 7 Dec. The red arrows track the Low back to 2 Nov.

 

The HIGH managed to keep winds mostly light NW for yachts arriving in northern NZ from the tropics in the past week (except for last Tuesday night with a passing front).

 

The wild weather is expected to cross the North Island overnight tonight, then weaken away.

-=-=-=-=

The Tropics

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

 

Active cyclones at present is AMBALI and BELNA in South Indian Ocean. AMBALI almost broke the Global record for central pressure drop , intensifying from cat 2 to borderline cat 5 in 24 hours. (PATRICIA holds the global record) . At one stage last week there were 5 tropical systems in the West Indian Ocean.

 

There is potential for cyclone formation showing in the Coral sea and about around Guam.

 

WATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to be active in the north Coral Sea and from Samoa to southern parts of French Polynesia, mainly stretching from Solomons, across northern Vanuatu to between Fiji and Samoa to Southern Cooks.

 

Subtropical ridge (STR)

HIGH east of NZ over 1025hPa is expected to finally move a little to the east on Monday a n d then hover around 40 to50S 150E until Sun 15 Dec.

Next High is expected to enter the Tasman Sea (from East Aus) on Monday and slowly spread east, reaching Northern NZ on Thu and Fri then further east on Sat and Sunday.

 

Tasman Sea /NZ/Aus

Trough crossing North island tonight, followed by SW S flow on Tuesday and Wednesday, the light winds from a passing high on Thursday /Friday. Next trough from the Tasman is expected over northern NZ on Sat/Sun/Mon 14/15/16Dec local followed by a SW flow for several days. .

 

For Noumea to Aus: With mainly High pressure in Tasman Sea this week it OK until Thursday. However, passing trof 1009 over Noumea this weekend/early next week.

 

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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

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

01 December 2019

Bob Blog 1 dec 2019

WEATHERGRAM

YOTREPS

Compiled Sun 01 Dec 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 THE LAST MONTH

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

 

The anomolies in the North Pacific are unchanged. There continues to be a build-up in heat in the Tasman Sea. And sea-temperatures around Galapagos are on the warm (El Nino) side of normal.

 

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 subtropical ridge in the southern hemisphere has expanded southwards. The area below 1010hPa in the equatorial area has also expanded southwards.

 

Higher than normal air pressure over arctic and Antarctic are helping send cold air equator-wards into the mid-latitudes. There are four low-pressure anomolies around the Southern hemisphere mid-latitudes. Siberian High has formed stronger than normal.

 

Zooming into the NZ area, and comparing monthly anomalies from last month with now,(but with a change of colouring), shows that the subtropical ridge STR has strengthened and expanded southwards, but the 1010 isobar is still over central NZ .

 

It remains most intense over SW of Australia, most intense spot has shifted from eastern Australia to west of Australia. Isobars over NZ have weakened, with the 1010hPa isobar in much the same place as last month, and 1005 hPa now further south. Now a NW anomalis flow over NZ

 

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The Tropics

The latest cyclone activity report is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html (but not this weekend)

Active cyclones at present is KAMMURI aiming for northern Philippines.

 

WATHER ZONES

SPCZ=South Pacific Convergence zone.

Tropical cyclone RITA briefly reached Cat 1 (the lowest) just east of northern Vanuatu last week, so our cyclone season has started.

The SPCZ is expected to have a normal week, mainly stretching from Solomons, across northern Vanuatu to between Fiji and Samoa to Southern Cooks.

There is expected to be a passing trough further east.

 

Subtropical ridge (STR)

HIGH east of NZ over 1025hPa is expected to linger near 35S 160W this week. maintaining a disturbed NW flow over the North Island.

Next High is expected to enter the Tasman Sea (from East Aus) over the coming weekend 7-8 Dec.

 

Tasman Sea /NZ/Aus

Deep lows, one dropping to maybe 951 by Tuesday local, way south in the Southern Ocean, are expected to maintain a series of fronts on the Tasman Sea /NZ area. The quasi-stationary HIGH east of NZ should keep a lot of the rain away from NE of NZ.

One of those fronts may turn into a low in mid-Tasman that may visit NW NZ by Sunday 8 Dec local, 1002 hpa, followed by SW winds early next week, avoid arriving then.

 

For Noumea to Aus: Mixed bag this week, Northerly winds until Wednesday, then light wind then southeast winds from Sunday 8 Dec. OK to go, but may need waypoints,

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

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

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

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

Contact is bob@metbob.com or txt 6427 7762212

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

24 November 2019

Bob Blog 24 Nov

WEATHERGRAM

YOTREPS

 

Compiled Sun 24 Nov 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.

 

LIGHTNING

 

The following notes have been summarized from a blog by Marshall Shepherd at

 

www.forbes.com/sites/marshallshepherd/2019/06/10/the-science-of-keeping-safe-indoors-and-outside-from-a-lightning-strike/#1e9a34a56102

 

Most lightning flashes (roughly 80% or so) are intracloud (IC), either cloud-to-air (CA) or cloud-to-cloud (CC). It is the cloud-to-ground (CG) lightning flashes that pose a risk to us.

 

Lightning is a giant spark of electricity in the atmosphere between clouds, the air, or the ground. In the early stages of development, air acts as an insulator between the positive and negative charges in the cloud and between the cloud and the ground. When the opposite charges builds enough, this insulating capacity of the air breaks down and there is a rapid discharge of electricity that we know as lightning.

 

Here are the 5 steps that occur in a cloud-to-ground strike:

 

1. A channel of negatively charged ions surge toward the ground in very distinct steps. This is called a stepped leader.

2.As the stepped leader (and its various branches) move toward the ground, it attracts streamers of positive charge from the ground.

3.The electrical potential of the stepped leader connects to the ground, tree, building, or whatever is available in the pathway. The negative charge starts to flow down the pathway.

4.A return stroke explodes "up" the pathway or channel, and this is what we actually see as the lightning stroke. It happens so fast that you may not easily discern the direction of propagation.

5.If there is enough charge left in the cloud, subsequent dart leaders can use the same pathway created by the initial stepped leader. The return strokes associated with dart leaders are why lightning seems to flicker.

 

The atmosphere is a very good insulator, so lightning seeks the path of least resistance. Because the atmosphere is a good electrical insulator, lightning is looking for the path of least resistance. Lightning often strikes taller objects like trees, buildings, antennas, and metal poles For this reason, we often advise you to get inside if possible. If you are caught outdoors during lightning, and if no shelter is available, crouch low, with as little of your body touching the ground as possible.

6.Stay away from plumbing or water pipes. Metal piping conducts electricity.

7.Don't get near electrical equipment like televisions, stereos, or the other fancy smart electronics in homes today.

8.Avoid concrete walls and flooring. Concrete is often supported by metal rods or frames.

9.Don't use a corded phone, however cellular or cordless phones are fine.

 

Here is a summary of “A Detailed Analysis of Lightning Deaths in the United States from 2006 through 2018.” (John Jensenius, Jr)

 

During this 13-year period fishermen accounted for more than three times as many fatalities as golfers, while beach activities and camping each accounted for about twice as many deaths as golf. From 2006 to 2018, there were a total of 38 fishing deaths, 23 beach deaths, 19 camping deaths, and 17 boating deaths. Of the sports activities, soccer saw the greatest number of deaths with 12, as compared to golf with 10. Around the home, yard work (including mowing the lawn) accounted for 18 fatalities. For work-related activities, ranching/farming topped the list with 19 deaths.

 

While these results may be surprising, there were other results that were not. For example, males account for more than 80% of the fatalities, and weekends are the time of week most likely to experience a lightning fatality.

 

Myth: If it’s not raining, there will be no lighting

FACT: Lightning can occur without rain—often happens in Australia triggering bush fires.

 

Myth: Rubber tires on a car or rubber shoes protect against lightning

FACT: It’s the metal surrounds of a car that acts as a Faraday cage, protecting you from lightning when inside (just don’t touch the radio).

 

Myth: people struck by lightning carry an electrical charge and shouldn’t be touched.

FACT: No, they don’t. It’s safe and necessary to help them immediately. Lightning can disrupt or stop the heart rhythm and may require a defibrillator. If someone has stopped breathing after a lightning strike, start CPR and call 111.

 

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The Tropics

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

Active cyclones at present are FUNG WONG and SEBASTAIN (now in mid-North Atlantic and remains are aiming for UK).

Large potential for development this week over the Guam area and east of northern Vanuatu (along 70E).

 

WATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is very active to north and NE of Vanuatu with a tropical Low NE of northern Vanuatu. This Tropical low is likely to deepen and may become a Cyclone for next few days as it travels south along around 170E, skirting the eastern edge of Vanuatu. Should fade by end of the week and drift west across mid or south Vanuatu.

Another Convergence zone is expected to hover around southern Cooks/ southern French Polynesia .

 

Subtropical ridge (STR)

HIGH over northern NZ on Monday is expected to travel off to the east along 40s this week.

Another HIGH is expected to enter the Tasman sea on Wed and cross northern NZ on Sun 1 Dec.

 

Tasman Sea /NZ/Aus

Trough crossing northern NZ on Wednesday night followed by S/SE winds on Thursday /Friday then light winds over the weekend from incoming High. Next trough is likely mid-next week (3-4 Dec) preceded by NW winds that may get strong west of northern NZ on Tues 3 Dec. OK for sailing from Fiji /Tonga to NZ this week, with waypoints to handle the changing winds near NZ.

For Noumea to Aus: OK to o next few days but remains of that possible cyclone on Sun /Mon /Tues 1/2/3 Dec with variable winds.

 

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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

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

 

17 November 2019

Bob Blog

WEATHERGRAM

YOTREPS

Compiled Sun 17 Nov 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.

 

SAM

We have had a taste of winter in New Zealand late August/early September, followed by a few weeks with disturbed lows and fronts, but this week is looking more on the HIGH side.

A good parameter to watch, to forecast southerly blasts is the Southern Annular Mode (SAM), or its proxy called the Antarctic Oscillation (AAO), SAM describes the north to south movement of the westerly wind belt that circles Antarctica, so it can be used as a predictor for cold air reaching our mid-latitudes.

When SAM is positive, the belt of strong westerly winds contracts towards Antarctica. This results in weaker than normal westerly winds and higher pressures over mid latitudes, limiting the northern extent of cold fronts.

A negative SAM event indicates an expansion of the belt of strong westerly winds into the mid-latitudes. This weather pattern results in low pressure systems over mid-latitudes such as New Zealand, with more (and stronger) storms.

We can see the latest forecasts for the AAO (a good proxy for SAM) at

www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/new.aao_index_ensm.html

 

There was a Sudden Stratospheric warming over Antarctica, and that encourages streamers of cold air to break off Antarctica into the Southern Ocean and further north at times. The SAM index shows this with its negative values since last October, and even the forecast for the next week or so is for negative SAM. Yuck.

 

=============================

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

Active cyclones at present are KALMAEGI, FENGSHEN and RAYMOND

Large potential for development this week over the Guam area.

 

WATHER ZONES

SPCZ=South Pacific Convergence zone.

 

The SPCZ is expected to stretch from PNG to Samoa ---a tropical Low is expected to form NW of Fiji by Wednesday. Its future is uncertain, but there is a good chance it may onto Fiji or Vanuatu next week, so get some updates.

 

There is also a convergence zone over Australs and Gambiers this week.

 

Passing trough over Tonga on Friday, expected to travel east followed by light variable winds.

 

Subtropical ridge (STR)

HIGH in north Tasman sea is expected to fade on Tuesday.

Another HIGH is expected to move into South Tasman Sea on Wednesday and stall in the Tasman Sea until maybe Tues 26 Nov.

Tasman Sea /NZ/Aus

Trough crossing northern NZ on Monday, a brief ridge of light winds on Tuesday, then another trough on Wednesday. That second trough is expected to develop a Low east of NZ from Thursday to Monday, travelling NE. This maintains a southerly wind between NZ and Tonga, so not good for getting to NZ.

For Noumea to Aus, OK this week with trade winds.

 

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

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

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

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

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

Contact is bob@metbob.com or txt 6427 7762212

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

10 November 2019

Bob blog 10 Nov

WEATHERGRAM

YOTREPS

Compiled Sun 10 Nov 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.

OCTOBER above

The state of the ENSO

The Southern Oscillation Index SOI sums up the weather pattern over the South Pacific as one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin.

SOI (30 day running mean) touched El Nino territory in mid-September but is now relaxing.

It was below -10 units on this Australian scale for  4 weeks. 

 

 SOI trend (x10) since 2016 showing us in neutral territory as at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the widest and warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. When SST in the target zone (equatorial Pacific between dateline and Galapagos) are notably cooler/warmer than normal, this is called a La Nina/El Nino episode.

 

 Sea surface temperature anomaly as seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=nino34&p=monthly

Nino 3.4 index has been in neutral territory since May, and spent 4 weeks cooler-than-normal in September.

SO both SOI and NINO3.4 parameters are in neutral territory for now. For  an outlook on  the possible  future,  go  to

iri.columbia.edu/our-expertise/climate/forecasts/enso/current/?enso_tab=enso-sst_table

which shows an erratic future with 1 model going for an El Nino and another for almost a La Nin, but most models staying in neutral territory.

 

=============================

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

Pray tonight for those being hammered by cyclones such MATMO over Bangladesh, and NAKRI over Vietnam.  At least HALONG is staying over a mostly open ocean.

Large potential for development  this  week over the  Guam  area.

 

WATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stretch from PNG to Samoa and then to Southern Cooks.

Passing convergence zone trough over Australs and Gambiers this week.

Passing trough over Fiji tonight, Tonga on Tuesday,  and fading by Thursday.

 

Subtropical ridge (STR)

HIGH is expected to linger east of NZ near 40S 160-150W until midweek then move off to the east.  Has enhanced trade winds on its north side, but not intense enough for a squash zone.

Next HIGH should form near 30S  in North Tasman on Monday and  travelling east, passing north of  NZ on Wednesday  then  fading from  Thursday,  but lingering as  a ridge over  northern  NZ for  the  weekend.

 

Tasman Sea /NZ/Aus

Trough crossing northern NZ tonight and Monday. Ridge on Wednesday, then another trough on Thursday. A lingering ridge for the weekend., then a NW flow for most of next week.

Good to depart tropics this week for NZ – but after the passing trough (reaching Tonga on Tuesday).

For Noumea to Aus, OK this week if you time your trip around the travelling  High.

Avoid arriving in  Australia  on Sat/Sun 16/17 Nov due  a passing trough/low

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

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 November 2019

Bob Blog 3 Nov

WEATHERGRAM

YOTREPS

Compiled Sun 03 Nov 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 THE LAST MONTH

Sea Surface temperature anomalies as at start of October compared with the start of November  may be seen at www.weatherzone.com.u/climate/indicator_sst.jsp?lt=global&lc=global&c=ssta

 

The anomolies in the North Pacific are starting to relax. There is a new build up in heat in the Tasman Sea and  Southwest Indian ocean

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

 

There has been a change in the anomaly pattern during the last month, with a relaxation of the High anomaly over Australia, and the swap, south of Africa, from higher-than-normal to lower-than-normal.

Zooming into the NZ area, and comparing monthly anomalies for end of last month with now, (but with a change in the colour scale), shows that the subtropical ridge STR has weakened and it’s most intense spot has shifted from eastern Australia to west of Australia.   Isobars over NZ have weakened, with the 1010hPa isobar in much the same place as last month, and 1005 hPa now further south. There is still mainly a SW flow over NZ, but it’s weaker than it was.

 

===============================

THE TROPICS

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

At present there are there named storms MAHA, MATMO(weakening), and HALONG, and strong potential areas in China Sea and around Guam.  

 

WATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to have an active week over PNG, some activity over northern Vanuatu and northern Fiji, and be weaker than normal further east to Samoa.

Weak convergence zone between Samoa and French Polynesia at times this week.

Burst of SSW swell around 3m affecting as far north as 18S this week due to a deep low near 40S.

 

Subtropical ridge (STR)

HIGH is expected to cross northern NZ by Tuesday and then travel east along 30 to 35S. 

Next High from Australia may reach Tasman sea by Sun 10 Nov.

 

Tasman Sea /NZ/Aus

Trough over eastern Aus coast with thunderstorms on Sunday/Monday turning into  a Low east of Coffs by Tuesday then going off to  S and fading on  Wednesday.  Broad trough in Tasman by Friday, crossing NZ and Fiji on Mon 11 Nov.

For Noumea to Aus, no good this week:  has a passing trough that reaches Noumea around Wednesday. Then westerly winds along the route

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

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

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

27 October 2019

bob Blog 27 Oct

WEATHERGRAM

YOTREPS

 

Compiled Sun 27 October 2019

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

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

 

THE TROPICS

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

At present there are two named storms PABLO and KYARR

 

WEATHER ZONES

SPCZ

The SPCZ is expected to stretch from PNG to north of Vanuatu with another zone stretching from Samoa area to Sothern Cooks.

Weak Passing trough over Fiji/Tonga on local Wednesday and Niue/ Southern Cooks area on local Wednesday (one day later) area on local Tuesday, Cooks on Wednesday and French Polynesia on local Thursday.

 

Subtropical ridge (STR)

HIGH is expected to travel east along 30S from Tasman Sea to East of NZ from Wednesday to Sunday this week.

 

Tasman Sea /NZ/Aus

Weak trough is expected to cross NZ on Monday followed by SW flow on Tuesday and Wednesday and then a large HIGH is expected to travel from Tasman Sea across NZ from Thu 31 Oct to Tue 5 Nov = good days for arrival in NZ.

  After that the next trough is now due on 6/7 Nov - probably worth avoiding.

Then a NW flow, OK for arrival, for 8/9 Nov.

 

For Noumea to Aus looks Ok, with HIGH in Tasma Sea. No passing troughs to avoid.

 

Tahiti to Tonga

The passing trough is likely to reach Southern Cooks area by local Wednesday and then develop a Low just south of the Cooks on Thursday and this lo should the deepen and go south or SSE. Avoid.

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

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

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

20 October 2019

Bob Blog 20 oct

WEATHERGRAM

YOTREPS

 

Compiled Sun 20 October 2019

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

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

 

THE TROPICS

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

At present there are two named storms in the Northwest Pacific Ocean NEOGURI and BUALOI

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stretch from PNG to north of Vanuatu and north of Fiji, maybe touching Samoa.

Passing trough over Niue area on local Tuesday, Cooks on Wednesday and French Polynesia later in the week.

 

Subtropical ridge (STR)

HIGH is expected to travel east along 30S from Tasman Sea to East of NZ from Wednesday to Sunday this week.

 

Tasman Sea /NZ/Aus

Low is expected to form over central NZ on Tuesday night and travel on Wednesday to east of NZ followed by a SW flow on Thursday and then a ridge on Friday. Next trof for northern NZ (no good for arrival in NZ) is due on 4 November.

As for tropics to NZ this week: Time your voyage to run south when High travels east (wed to sat), before that the trip has southerly winds which are Ok for getting west, but not south.

For Noumea to Aus looks Ok, but avoid arriving on coast from around Brisbane southwards on Saturday afternoon 26 oct due passing trough. This trough should weaken as it moves across Tasman, reaching New Caledonia by following Tuesday.

 

Tahiti to Tonga

Mainly trade winds this week but for a passing trough at some stage during the week, followed by SW/SSE winds .

 

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

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

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

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

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

Contact is bob@metbob.com or txt 6427 7762212

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

 

 

13 October 2019

Bob Blog 13 Oct

WEATHERGRAM

YOTREPS

 

Compiled Sun 13 October 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.

 

Coming cyclone Season Outlook

 

NIWA and MetService NZ have published their combined outlook for the coming South Pacific Cyclone season and the full details are at :

 

https://www.niwa.co.nz/climate/southwest-pacific-tropical-cyclone-outlook/southwest-pacific-tropical-cyclone-outlook-october-2019

 

Briefly:

A slightly more active than normal season with 9 to 12 named storms expected.

Extra activity is expected east of the dateline (Samoa/Tonga / Niue/ Southern Cooks) especially for Feb -April 2020.

In previous similar (“analogue”) years there have been some CAT 5 storms, so the indications are this season cyclones may be more intense than normal. But next three months are expected to be close to normal, and the season starts at low risk.

 

THE TROPICS

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

At present there are three named storms active cyclone HAGISIS off Japan, EMA in Mid-North-Pacific and MELISSA in northern north Atlantic.

HAGIBIS as the largest and most active storm Japan has had in decades and caused cancellation of some Rugby world cup games , and the practice session for F1. .

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is rather weak wet of the dateline this week, but active between Samoa and noticeable between Suwarrow and Tahiti.

Passing trough over Fiji/Tonga area on Monday /Tuesday

 

Subtropical ridge (STR)

The STR remains near 20S in the NZ area .

HIGH to E of NZ on Monday moves off to the east.

Next HIGH starts forming in Tasman Sea on Mon/Tue/Wed and travels east along 30S from Thursday/Friday/Sat to east of NZ, leaving a tongue of ridge behind it. This brings a period of light winds north of NZ>.

 

Tasman Sea /NZ/Aus

Low deepening to 986 hPa as it travels southeast over northern NZ on Mon/Tue , moving east of NZ and starting to weaken on Wednesday.

Brief ridge on Thursday then next trough on Fri/Sat.

As for tropics to NZ this week: light winds from that High/ridge this week, large 3m+ swells as far north as 25S on Wed, and avoid arriving in NZ around 24 October. Remember that Oct 25 is a holiday in NZ.

For Noumea to Aus looks Ok after westerly winds swing to S/SE near New Caledonia on Monday.

 

Tahiti to Tonga

Mainly trade winds this week but passing trough over Tonga on Tuesday with showers.

 

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

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 October 2019

Bob Blog 6 Oct 2019

WEATHERGRAM

YOTREPS

 

Compiled Sun 29 September 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 THE LAST MONTH

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

 

The peak heat of the northern summer/autumn has gone now and sea temperatures are relaxing and easing towards normal, but still slightly above,

 

In the Southern hemisphere there’s a large zone of cooler sea off the west of South America, and temperatures between Queensland and Northern NZ, and a return to normal temperature off the west of Australia.

 

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 southern subtropical ridge is much the same as last month. It is much stronger off to west of South American, and slightly stronger in the Tasman sea. . The monsoonal trough is a little further east and weaker.

 

Zooming into the NZ area, and comparing monthly anomalies for end of last month with now, shows that the subtropical ridge STR is in much the same place but slightly stronger than a month ago. There is still a SW flow over NZ, but it’s weaker than it was.

 

THE TROPICS

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

At present there is one active cyclone HAGISIS off Japan and expected to skim along Japan East coast.

Looks like we are having a lull in the cyclone season.

 

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to visit Fiji on Monday and the Tonga /Minerva area on Tuesday, then return north to Solomons to Tokelau stretch from Solomon Islands to Tuvalu /Tokelau, similar to last week.

Weak upper trough 1012 over Tahiti on Wednesday with showers.

 

Subtropical ridge (STR)

The STR has retreated to 30S around NZ

HIGH to NE of NZ on Monday stalling and extending south near 170W/south of Southern Cooks on Tuesday to Thursday

Next HIGH is in Southern Ocean and expected to travel east along 50S to south of NZ on weekend 12/13Oct. 6,

 

Tasman Sea /NZ/Aus

Intense Low deepening in central Tasman Sea on Tuesday/Wednesday and crossing South Island on Thursday. Another trough/Low crossing northern NZ on Friday

Maybe another Low in northern Tasman Sea / Northern NZ early next week, not sure yet.

As for tropics to NZ this week, wait until Wednesday or latter for departure. Avoid arriving early next week (possible low)

For Noumea to Aus or vice versa: complicated thus week by passing trough.

 

Tahiti to Tonga

The passing upper trough 1016hpa+ hPa may bring some showers.

Trade winds expected this week, a good week to go west.

 

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

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

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

29 September 2019

Bob Blog 29 Sep

WEATHERGRAM

YOTREPS

Compiled Sun 29 September 2019

 

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

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

 

THE TROPICS

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

At present there are three active Cyclones LORENZA in the mid north Atlantic, NARDA heading for Baja California and MITAG near Japan, and a few areas of potential activity in North Pacific. ‘Looks like we are heading for a lull in the cyclone season.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stretch from Solomon Islands to Tuvalu /Tokelau, similar to last week.

Passing trough 1012-16hPa over Tonga on Tongan Tuesday, Palmerston on Local Wednesday, and Southern Cooks and parts of Tahiti on local Thursday/Friday followed by SE winds.

Heads up that a bigger passing trough 1008-1012 hPa is expected the following week.

 

Subtropical ridge (STR)

The STR has retreated to 30S around NZ

HIGH to NE of NZ on Monday travelling east along 30S around 1024, so no squash zone.

Next HIGH forming in Tasman Sea by Tuesday travelling NE to 30S by Friday the fading but followed by another HIGH on Friday/Saturday.

 

Tasman Sea /NZ

Intense Trough over northern NZ on local Monday, followed by a SW/WSW flow until Thursday. swell until Friday, strong on Wednesday, easing by weekend.

HIGH in N Tasman Sea should ridge towards northern NZ on Thursday/Friday.

Another Front is expected over Southern NZ on Friday and central/northern NZ by Saturday, followed by a southerly flow.

Reasonable for voyages from tropics to NZ departing this week. Voyage will need waypoints.

 

Noumea to Aus: S to SSE winds at Noumea on local Monday Tuesday in wake of a passing trough then SE winds expected from Wednesday onwards , Ok for going to Aus,.

 

Tahiti to Tonga

The passing trough 1012=1016hpa later in the week doesn’t really have much wind swing at the surface, so can depart any date this week with mainly trade winds.

However a deeper trough 1008-1012hpa is expected to reach Tonga around Sunday 6 oct followed by SE winds, and then travel east, so may need to arrange some positioning waypoints for that.

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

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

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

 

22 September 2019

Bob's Blog

WEATHERGRAM

YOTREPS

 

Compiled Sun 22 September 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.

 

Equinox is tomorrow NZ time. Monday at 7:50pm ( 25 0725 UTC)b

At this point in time the overhead sun is directly over the equator, shifting from the northern hemisphere to the southern hemisphere.

If you check sunrise /sunset times for your place for Mon 23 Sep, you will find that these compute to something like 12hr 7mins of sunlight. This is because sunrise and sunset are defined with respect to the top limb of the sun, rather than the centre of the sun, and that adds a few minutes of sunlight to the day. You’ll find (if you look) that the day that has closest to exactly 12 hours of daylight, called the equilux, is around three days earlier than the September equinox.

In New Zealand, the change to NZDT Daylight time occurs at 2am (becomes 3am NZDT) on the last Sunday of September, and so that’s 29 September. Clock goes forward I hour.

The change to daylight saving occurs on different dates for the nations around the South Pacific so I think it’s a good idea for you to have a summary for reference

 

Date Place Daylight saving time zone

29 Sep New Zealand UTC+13 (NZDT)

29 September Samoa UTC+14 (NZDT

29 Sep Chatham Islands UTC+13h45mins (CHADT)

6 Oct New South Wales, Tasmania UTC+11 (AEDT)

6 Oct Lord Howe Is. UTC+11 (AEDT) (30 minute ahead)

6 Oct Norfolk Island UTC+12 (AEDT)

10 Nov Fiji UTC+13 (Fiji Summer Time FJST)

No changes in Tonga or American Samoa or Vanuatu or Queensland/Northern Territory/Western Australia or New Caledonia.

 

As yachts start their end-of-spring migration, with the approaching South Pacific Cyclone Season, nominally on 1 November (starting at low risk). it is also useful to have a summary of the various national holidays, as these limit available departure dates.

 

From East to west

French Polynesia 1 Nov All Saints Day, 11 Nov Armistice day

Cook Islands: Mon 28 Oct Gospel day

Niue: Oct 19 to 22 Constitution day celebrations, Oct 25 is Gospel day.

Tonga Nov 4 Constitution Day

Fiji Oct 10 Fiji Day, Oct 28 Diwali, Nov 11 Prophet Mohammed’s Birthday.

New Caledonia Sep 24 National Day, 1 Nov All Saints Day, 11 Nov Armistice Day .

New Zealand Oct 22 Labour day.

Australia: OCT 7 Labour Day (ACT, NSW &SA), Queen’s Birthday (QLD)

 

THE TROPICS

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

 

At present there are five active Cyclones JERRY and LORENA and MARIO and KIKO and TAPAH and several areas of potential activity in North Atlantic and North Pacific. ‘

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stretch from Solomon Islands to Samoa.

Squash zone of enhanced SE winds on north side of a passing HIGH on MONDAY from Vanuatu to Samoa/Tonga easing on Tuesday.

Passing trough over southern Cooks/ parts of Tahiti on local Sunday/Monday followed by fresh SE winds on local Monday.

 

Subtropical ridge (STR)

The STR briefly visited 40S over NZ last week. It is returning to north of NZ this week

HIGH to NE of NZ on Monday travelling east along 30S around 1024, so no squash zone.

Next HIGH forming in Tasman Sea by Wednesday to travelling NE to 30S then travelling east past northern NZ by Sunday.

 

Tasman Sea /NZ/Aus

Trough over northern NZ on Tuesday, followed by a SW swell until Friday, strong on Wednesday, easing by weekend.

Another Front is expected over northern NZ Monday 30 Sep followed by southerly winds reaching as far north as Fiji by Wednesday 2 October and Tonga by Thursday 2 October. No good for trips from tropics to NZ arriving next week.

For Noumea to Aus: OK at first but interrupted by a passing trough on Sunday Monday 29/30 Sep with light winds/

 

Tahiti to Tonga: Try and time your voyage after the passing trough (affecting parts of Tahiti on local Sunday /Monday) so depart from Tuesday.

 

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

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

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

15 September 2019

Bob Blog 15Sep

WEATHERGRAM

YOTREPS

Compiled Sun 15 September 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.

 

SAM

 

We have had a taste of winter in New Zealand late August/early September, followed by a few weeks with disturbed lows and fronts, but this week is looking more on the HIGH side.

 

A good parameter to watch, to forecast southerly blasts is the Southern Annular Mode (SAM), or its proxy called the Antarctic Oscillation (AAO), SAM describes the north to south movement of the westerly wind belt that circles Antarctica, so it can be used as a predictor for cold air reaching our mid-latitudes.

When SAM is positive, the belt of strong westerly winds contracts towards Antarctica. This results in weaker than normal westerly winds and higher pressures over mid latitudes, limiting the northern extent of cold fronts.

A negative SAM event indicates an expansion of the belt of strong westerly winds into the mid-latitudes. This weather pattern results in low pressure systems over mid-latitudes such as New Zealand, with more (and stronger) storms.

 

We can see the latest forecasts for the AAO (a good proxy for SAM) at

www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/new.aao_index_ensm.html

Showing a swing to positive SAM and likely HIGHS in the subtropics.

 

 

 

THE TROPICS

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

For those who want to see the President of US comment on DORIAN possibly hitting Alabama

See www.google.com/search?q=trumps+Dorian+track&oq=trumps+Dorian+track&aqs=chrome..69i57.220763j0j7&sourceid=chrome&ie=UTF-8

 

At present there are two Cyclones HUMBERTO and KIKO and several areas of potential activity in North Atlantic and North Pacific.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

 

The SPCZ is expected to stretch from Solomon Islands across northern Vanuatu to a weaker Convergence zone around Tuvalu and Tokelau.

 

Trough over Tonga on local Monday connected to a Low near 30S This Low is expected to travel east along 30S to 160W by local Wednesday. and then go south. Associated trough is expected to visit Niue on local Monday. Palmerston Island area on local Tuesday and affect Tahiti area with variable winds on local Tuesday night /Wednesday.

 

Subtropical ridge (STR)

The STR is expected to return to 40S thus week, but not until mid-week.

On Mon and Tuesday, a High is expected to travel east along 30S across northern NZ then fade.

Then from late Tuesday to Sunday another HIGH is expected to form near 40S in the Tasman Sea and take it’s time travelling onto South Island before going north to 30S and to East of NZ.

There may well be a squash zone in the tropics on the north side of this High NEXT WEEK>

 

Tasman Sea /NZ/Aus

Trough (between the HIGHS) over northern NZ on Tuesday, followed by a burst of a long-period SW swell from Tasman to north of NZ on Friday. Should be Ok for trips from Fiji/Tonga to NZ this week.

SE to East winds  OK from Noumea to Australia. No good going other way.

 

Tahiti to Tonga

Try and time your voyage taking into account the passing trough. It misses Suwarrow.

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

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

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

08 September 2019

Bob Blog

WEATHERGRAM

YOTREPS

Compiled Sun 08 September 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.

 

Parts of a depression.

A depression is a zone where the isobars are depressed below normal. The average surface air pressure in 1013.25hPa and nearest isobar too that is 1012hPa—The 1012hpa is usually the straightest on the weather map, dividing anticyclones or anticyclonic flow with higher isobars -- from cyclones or cyclonic flows with lower isobars.

The same thing is called a Cyclone when referring to its winds rather than it’s isobars. It is also called a Low.

 

Lows come in many shapes and sizes and their intensity (of wind and rain) may be related to the central pressure. The lower this is. the more the intensity. Other factors are the cloud width and shape, and , for tropical cyclones there is Category ( a wind scale), or Dvorak code (size and cloud extent) or ACE (accumulated cyclone energy), Cyclone DORRIAN has a central pressure as low as 910hpa.

 

A low in the Tasman Sea today with a central pressure of 990hpa is a good demonstration showing the parts of a mid-latitude depression (not a tropical Cyclone). It occurs when a stream of cold air from the Sothern Ocean (high density air collides with warmer more humid air in the Tasman Sa (lower density air). At the cold front on the eastern side of the system, higher density air pushes the lower density air up and out to eastwards, creating rising air = cloud and rain

 

The Cold Pool is formed by the upper air reflection of the surface low and is usually found N or NE on the surface Low (in the southern Hemisphere), It can easily be detected from satellite imagery as a circular area of thundery showers, formed by warm surface air rising quickly due to its extra buoyancy when there is colder than normal air aloft.

 

Between the front (which arrived like and express train this morning) and the cold pool (which arrived late this afternoon/evening) there is a zone with partial l sunshine and no rain which is called the “Dry slot”. Most fronts are followed by dry slots and they can become a sailor’s friend, so long an you to brace for the cold pool that may follow.

 

After the Cold pool comes the “Back side” of the Low with its curl of cloud containing another dose of rain.

 

And on the south side of the low there is the frontal occlusion . This zone may become very slow-moving so that even if it only has moderate rain intensity , its volume of rain may be larger than normal over a small area.

 

THE TROPICS

 

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

 

TC DORIAN hovered around the Bahama for more than 2 days, making 3 landfalls, and since then has been skirting east coast of North America. It also marked a surge in Cyclone activity: there are now FIVE cyclones, and several areas of potential activity in North Atlantic and North Pacific. There is also a zone of potential development around the Solomon Islands, but models are quiet there.

 

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to hover over PNG and Solomon Islands, with quieter convection hovering around Fiji this week.

Passing trough, with northerly winds swinging to southerly winds, now crossing eastern Fiji on local Monday is expected to go SE and reach Tonga by Wed/Thu local date and then Niue the next day (Wed local date) but fade and not affect Aitutaki or Tahiti, but may affect Rarotonga on local Thursday/Friday..

 

Subtropical ridge (STR)

Yet another week with STR north of NZ.

Hight to NE of NZ is traveling east along 30 to 35S on Mon-Tuesday

Another High is expected to form off east of Sydney on Wednesday and then NE to 30S then east across northern NZ by local Friday.

 

Tasman Sea /NZ/Aus

Low down to 990 hPa in Tasman Sea is expected to cross northern NZ on Monday/Tuesday local, followed by S Wed/SW Thu//W/Friday. Then another low is expected to deepen in Tasman sea over weekend and cross over northern NZ on Mon 16 Sep.

Looks OK to sail from QLD to New Cal early this week in the winds following Monday’s low but no good from Wednesday when SE winds return, and it is then OK to go t’other way.

If sailing from tropics to NZ this week, then try and time your voyage to arrive in NZ between fronts – as is likely next week..

 

Tahiti to Tonga

Looks Ok to depart from Monday this week, may need to go north of the direct path to avoid lights winds. Early notice that next week may have a squash zone of enhanced winds.

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

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

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

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

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

Contact is bob@metbob.com or txt 6427 7762212

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

01 September 2019

Bob Blog 1 Sep 2019

WEATHERGRAM

YOTREPS

 

Compiled Sun 01 September 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 THE LAST MONTH

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

The main pattern changes are the ribbon of cooler than normal sea around the Galapagos. There is also a return to near normal in the Tasman Sea and a cooling off western Australia (an continuation of the Positive Indian Dipole).

 

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 southern subtropical ridge is much the same as last month. The monsoonal trough is a little further east. The trough around NZ has got bigger.

Zooming into the NZ area, and comparing monthly anomalies for end of last month with now, shows that the subtropical ridge STR is in much the same place but slightly weaker than a month ago. The anomalous trough over NZ has stronger SW flow over NZ than a month ago.

 

THE TROPICS

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

 

TC DORIAN is expected to hit Bahamas and then approach Florida, but may swing north and remain mainly offshore. For the latest see www.tropicaltidbits.com/storminfo/

 

There are several areas for potential development, especially around Bangla Desh, NW Pacific and west of Central America, --- as expected at this time of the year.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to hover over PNG and Solomon Islands, with another branch hovering around Tuvalu and Samoa.

Passing trough now crossing Tahiti is expected to be followed by a good SE flow on local Monday.

Passing trough, associated with Low approaching NZ, is expected to travel from New Caledonia today to Fiji on local Tuesday night to Tonga on local Wednesday night to Niue on local Wednesday night to Palmerston on local Thursday and then fade as it moves SE.

 

Subtropical ridge (STR)

Hight to E of NZ is traveling east along 30 to 35S and should hover to south of FP until end of the week.

There is a gap until the next high. It is expected to travel east into the Tasman Sea around Tuesday next week, but not before.

 

Tasman Sea /NZ/Aus

Low deepening in mid -N Tasman Sea on Monday SW flow is expected to travel SE across North Island on Tues/Wed/Thursday down to 990 hPa and then go south away from NZ deepening to 980hPa at 55S, followed by a SW flow. On Friday another Low may form in mid-N Tasman Sea and then travel east across North Island on Saturday. This may be followed by another Low on Monday.

Looks OK to sail from QLD to New Cal early this week in the winds following Monday’s low but no good from Thursday, from then OK for going from New Cal to QLD.

Sailing to NZ this week means skirting around several fronts.

 

Tahiti to Tonga

Looks Ok to depart from Monday this week, voyage is likely to encounter one passing trough, but should be able to skirt around it over the open sea.

 

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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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25 August 2019

Bob Blog 25 Aug

WEATHERGRAM

YOTREPS

 

Compiled Sun 25 August 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.

 

PUMICE

There was an eruption of a undersea volcano at 18.325S 174.365W or around 27nm NW of Vava’u early in August that has ejected a raft of pumice that drifted SW to be around 60nm west of Late island off west coast of Vava’u, affecting voyages from Vava’u to Fiji.

It seems to currently be drifting north slowly. and dispersing.

A write-up on this pumice is at earthobservatory.nasa.gov/images/145490/a-raft-of-rock

and an excellent sailor report about this pumice appeared on facebook on 15 Aug at tinyurl.com/yxgfutte

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SUDDEN STRATOSPHRERIC WARMING

Your may have heard that a “Sudden stratospheric warming (SSW) is occurring over the Antarctic south of Africa to Australia, and wondered what that means. It may buckle the Polar vortex so that some cold streamers from the Southern Ocean may travel onto Australia/NZ in September.

This has only been recorded in the Southern hemisphere twice before (Sep 2002 and Sep 2010) and both times saw temperatures in New Zealand plunge.

In the Southern Hemisphere during winter, a ring of stormy and freezing weather encircles Antarctica, spinning clockwise. This is called the Polar Vortex and extends into the stratosphere, 30 to 50km high, and it is usually very good at locking the cold close to the Pole.

 

Stratospheric winds at 70hPa (near 18km) on 27 Aug may be seen at earth.nullschool.net showing zone of calm distorting the Polar Vortex.

 

Sometimes the winds in the stratosphere temporarily weaken, or even reverse, leading to a zone of sinking air, which warms the stratosphere as it compresses downwards, and this is called a SSW. It may cause the Polar Vortex to buckle, which then filters down towards the surface and send out streams of Antarctic chilled air northwards. In this case the most likely time is early September into Australian bight, , but there may be ramifications throughout September for the Tasman Sea. .

 

Stratospheric warming mid-last week may be seen at www.newshub.co.nz/home/new-zealand/2019/08/weather-niwa-warns-rare-sudden-stratospheric-warming-to-blast-nz-with-icy-streamers.html

 

THE TROPICS

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

There are three active tropical cyclones., DORIAN heading for the Caribbean , IVO staying offshore of west coast of Mexico and BAILU fading on the coast of China.

There are several areas for potential development, especially around NW Pacific and in he North Atlantic--- as expected at this time of the year.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stretch from south of the Solomon Islands across northern Vanuatu to Tuvalu, and may visit north of Fiji early in the week.

Passing trough over Palmerston/Aitutaki on local Sunday (tomorrow) , and bora Bora on local Monday/Tuesday with mainly light winds.

Passing trough over Niue on local Tuesday, to Palmerston/Aitutaki local Wednesday, and Bora Bora/Papeete on local Friday/Saturday, with a swing to NE then SE winds.

 

Subtropical ridge (STR)

After several weeks, the STR is finally shifting south onto NZ. remains north of NZ this week, High is expected to travel east along 35S across Tasman sea on local Tuesday and northern NZ on Wednesday, then fades off to the NE.

Another HIGH is expected to travel east along 45S across the Tasman Sea on Thursday and Friday and then across NZ on Sat/Sun.

 

Tasman Sea /NZ/Aus

SW flow easing on Monday/Tuesday. Between the Highs, a trough is expected to cross NZ on Thursday and fade over the North island on Friday.

A low is expected to form off Sydney on Thursday and travel to the NE then E and may reach norther NZ(GFS model) or Southern NZ (EC model) by  mid-next-week.

OK to head for NZ so long as you can reach it before possible strong winds early next week.

From Noumea to Aus may encounter a passing trough followed by a period of up to strong southerly winds south of Brisbane .

 

Tahiti to Tonga

The burst of large SW swells that affects this route south of 20S today/tomorrow should ease by late Monday local time.

Voyage departing this week may encounter a passing trough, but this isn’t expected to be big deal.

 

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

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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