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

25 March 2018

Bob Blog for 25 March 2018

WEATHERGRAM

YOTREPS

 

Compiled Sun 25 March 2018

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.

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TROPICS

Cyclone MARCUS, after hitting Darwin as a CAT 2 system last week, intensified to a CAT 5 cyclone, but is now weakening.

See mashable.com/2018/03/21/cyclone-marcus-strongest-storm-2018/#GOM9uShzdiqQ

 

NORA has moved onshore from the Gulf of Carpentaria onto northern Australia and is now weakening.

 

IRIS formed over Vanuatu is the past few days and is now travelling south across the Coral Sea. It is likely to encounter a jetstream on the northeast side of an upper trough by mid-week. This may well rip IRIS apart, but some models are indicating that the surface part of this system may then travel west or east for a few more days.

 

And a cyclone is now starting to form in Micronesia and is expected to travel north then northeast this week

 

A comparison of the weekly rain map from last week with the previous week shows the path of the cyclones and some heavy rain around Hawaii. Notice that the “equinoctial convergence zone” between south of Galapagos and Marquesas is still there.

 

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

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

 

The SPCZ is at the south-end of its range this week, covering New Caledonia, Fiji and Southern Tonga/Niue.

 

A LOW is expected to form on the SPCZ near 25S to south of Southern Cooks by mid-week, and then to travel off to the southeast.

 

Subtropical ridge (STR)

Large HIGH to east of NZ that dominated proceedings last week is expected to finally shift off to east along 45S.  There is likely to be a squash zone between this HIGH and the Low forming south of Southern Cooks.

New HIGH is expected to form in central Tasman Sea on Monday and Tuesday, then travel across central NZ on Holy Thursday and Good Friday. Then it is likely to fade east of NZ on Holy Saturday.

 

Around Tasman Sea

Low crossing south of Tasmania on Monday is likely to bring a gale to Bass Strait. As a consequence, the start of the Melbourne to Osaka yacht race has been delayed. Associated front is expected to cross South Island on Tuesday, and as a weak front over North island on Wednesday.

Another front is expected to travel onto South Island on Holy Saturday.

 

Panama to Galapagos /Marquesas

Today’s data the weather pattern is looking good for a departure from Panama any day this week.

Between the south of Galapagos and Marquesas there is the “equinoctial” convergence zone, mainly along 5 to 6S between 90W and 115W. Something to avoid.

 

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

Feedback to bob@metbob.com or txt 6427 7762212

I’m on Facebook at /www.facebook.com/metbobnz/

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, Subscribe/unsubscribe at the bottom.

Or, if email wasn’t from WordPress then send a reply email saying LEAVE.

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18 March 2018

Bob Blog 18 March 2018

WEATHERGRAM

YOTREPS

Compiled Sun 18 March 2018

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.

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A couple of weeks ago I mentioned Jimmy Cornell’s “Ocean Atlas”.

There is also an online site at www.pitufa.at/oceanwinds/  which gives the monthly averaged wins from scatterometer (satellite-derived) wind data.   The data only covers 5-10 years, so is of low quality but is well presented, so you can pan and zoom around the world’s oceans.  Left click on a spot to get a wind rose, and adjust the month at top right to quickly compare one month with another.  This offers a quick way for you to absorb the big picture.

 

EQUINOX

The Latitude of the overhead sun changes throughout the year. The sun is directly over the equator at Tuesday 20 March 1615 UTC (Wednesday morning 5:15am NZDT), and that’s the equinox.  Australia, New Zealand and Samoa switch from Daylight or Summer time to standard time on 1 April.

World Met Day

Another day worth noting this week is World Met day on 23 March. This marks the anniversary of the opening of the World Meteorological Organization as part of the UN in 1950.  This year’s theme is WEATHER READY, CLIMATE SMART, WATER WISE

See  public.wmo.int/en/resources/world-meteorological-day/wmd-2018

TROPICS

HOLA was briefly followed by LINDA in the Coral Sea, but LINDA was blown apart by strong upper winds.

Cyclone MARCUS hit Darwin as a CAT 2 system yesterday.

See www.theguardian.com/australia-news/2018/mar/18/cyclone-marcus-leaves-tens-of-thousands-in-darwin-without-power-or-drinkable-water

It’s been a while since Darwin has had strong winds, so the trees were easily damaged.

Possible future track for MARCUS may be seen at www.tropicaltidbits.com

In the South Indian Ocean ELIAKIM is moving southeast away for Madagascar.

 

A comparison of the weekly rain map from last week with the previous week, as seen at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, shows the path of cyclones HOLA and MARCUS, and a build-up of activity near Micronesia.  There is also a continuation of the “equinoctial convergence zone” between Galapagos and Marquesas.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to remain strong this week and extend all the way across the South Pacific from Solomon Islands to French Polynesia, but with small gaps.

A subtropical low is expected to form near 30S in the trough south of Southern Cooks by mid-week and then travel southeast.  This may become a recurring pattern over the next few weeks, affecting the route between NZ and Tahiti. So, anyone planning this route in next few months should watch how this low behaves.

 

A tropical low is expected to form in the Coral Sea late in the week, and probably travel to the southeast.

 

Subtropical ridge (STR)

Large HIGH east of NZ at start of the week should keep a ridge of settled weather over northern NZ until end of Tuesday. 

New HIGH is expected to travel east across Tasmania from Wednesday and to south of South Island on Friday/Saturday and the northeast to the east of NZ by early next week.

 

Around Tasman Sea

Trough from the SOUTHERN OCEAN is expected to move onto South Island on Tuesday and then stall near central and northern NZ with cold southerly winds from Wednesday to Friday.

 

Panama to Galapagos /Marquesas

Today’s data suggest a departure from Panama before 21 March may be better than  21 March onwards, because the winds near 6N are expected to fade away from 24 March.

Between Galapagos and Marquesas there is the “equinoctial” convergence zone, mainly along 4S between 90W and 105W.

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

Feedback to bob@metbob.com or txt 6427 7762212 or www.facebook.com/metbobnz/

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, Subscribe/unsubscribe at the bottom. Or send a reply email saying LEAVE.

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

11 March 2018

Bob Blog for 11 March 2018

WEATHERGRAM

YOTREPS

Compiled Sun 11 March 2018

 

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.

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

Just a brief blog this week, for I’m on holiday, touring the South Island.

 

TROPICS

We are waiting for the remains of HOLA to skirt past northern NZ on Monday/tomorrow. The dangerous quadrant of a southern hemisphere cyclone is the one that is FRONT LEFT of the travelling centre, where the speed of movement adds to the spinning winds. The faster the speed of movement, the greater the danger. It looks like the dangerous quadrant of HOLA may miss NZ

See www.msn.com/en-nz/news/national/cyclone-hola-may-not-make-nz-landfall/ar-BBK5vGt?li=BBqdk7Q&ocid=iehp

 

Around northern Australia, the monsoonal rain is continuing, and a Low is expected to form in the Coral Sea this week and drift somewhat to the south. Another Low is expected to form in the Gulf of Carpentaria, and travel west, maybe towards Darwin.

 

The rain map for last week, at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif,  shows the track of HOLA.  It also shows the formation of a convergence zone along 5South between Galapagos and the equator. This convergence zone tends to form around this time of the year because this is when the sun is directly overhead these latitudes. Now that it has formed, it may last for several weeks, and so I’ve nicknamed it the Equinoctial Convergence Zone.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to remain strong this week and help produce a Low in Coral Sea.

 

Subtropical ridge (STR)

HIGH is expected to form in central Tasman Sea on Tuesday/Wednesday and travel across northern NZ on Thursday.

Next HIGH is expected to form in Tasman Sea on Friday and move travel across central NZ on Sat/Sunday.

 

Around Tasman Sea

Remains of HOLA should skirt around the NE of NZ on Monday, followed by a Southwest flow on Tuesday.

After a cold front over South Island on Thursday and North Island on Friday, there may be a strong easterly flow over northern NZ on the south side of a Low.

 

Panama to Galapagos /Marquesas

A departure before Thursday may encounter a longer than normal period of light winds from 80W to 110W.

A departure after Thursday 15 March may have slightly better winds as far as 82W, maybe 85W.

 

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

Feedback to bob@metbob.com or txt 6427 7762212

I’m on Facebook at /www.facebook.com/metbobnz/

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, Subscribe/unsubscribe at the bottom.

Or, if email wasn’t from WordPress then send a reply email saying LEAVE.

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04 March 2018

Bob Blog 4 March

WEATHERGRAM
YOTREPS
Compiled Sun 04 March 2018
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.

For those who like to plan their voyages across the ocean well in advance, and decide to the nearest month when to reach where, according to the averaged weather, I recommend the NEW edition of Jimmy Cornell's "Ocean Atlas". JC has updated his popular atlas and sent me a demo copy as he asked me to review the South Pacific part. See cornellsailing.com/
I particularly liked the detail that has gone into the pilot charts, and the text on various matters such as weather and currents... and an interesting chapter about the various names for the winds around the world. The passage maps make this a valuable primary resource for all cruising sailors.
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Weather trend over the last month.
Sea Surface temperature anomalies as at 1st March may be seen at www.ospo.noaa.gov/data/sst/anomaly/2018/anomnight.3.1.2018.gif

The SST anomaly image still shows cooler than normal seas along the equatorial east pacific, but these are less than last month. So this La Nina is started to fade away in the Ocean.
The Tasman sea warm zone has been there since November and gave us our warmest ever measured summer. It too is starting to weaken. Cyclones during February have stirring the surface layer of the sea and mixed it with cooler temperature from underneath. This zone is still flecked with red spots as is much of the 40S latitude in the southern hemisphere. Interesting.
And the Gulf Stream off the east coast of North America is standing out as being much warmer than normal, this extra heat should energize storms over the northeast of North America.
To see how the annual weather cycle and the seasons are working out, check the average isobars for past 30 days and their anomaly isobar maps from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

FEBRUARY
The "beast from the east" has only been active for the past week and doesn't stand oy=ut in these 30-day averages.
The subtropical ridge over the South Pacific is still in place much as it was in January. The 1010hP (between light and dark blue) isobar has shifted north onto southern NZ, indicating that the northward seasonal shift of the subtropical ridge is already happening, and NZ should see the return of South/Southwest winds penetrating further north during March.
The last 30 days of rainfall, and its anomaly, is seen at TRMM at trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html

In the Pacific, both the ITCZ has an average position last month further AWAY FROM the equator than normal. This is typical of La NINA. Interestingly, the South Pacific convergence zone is somewhat north of normal (except where GITA visited Tonga, and tropical lows drenched southern parts of French Polynesia). In the Atlantic, the ITCZ is closer to the equator than normal.
TROPICS
TC DUMAZILE has formed in the Indian Ocean, indicating that a new pulse of MJO energy is forming there. It is off the east cat of Madagascar and expected to go southeast into the mid-latitudes and its remnants may reach 50S/Port-aux-Francais.

There is a tropical low between Fiji and Vanuatu. Some models have it deepening when it travels southwest towards Erromango/Tanna in southern Vanuatu on Wednesday/Thursday, and then recurving and travelling quickly southeastwards to east of NZ by late Saturday/Sunday 10/11 March.
To keep an eye on this feature follow Fiji Met Service at www.met.gov.fj/aifs_prods/20036.txt
Looking at the weekly rain maps from last week as at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif and the week before, we can see an increase in the intensity of the rain around Fiji to Niue, and in the ITCZ across the Pacific.
Around northern Australia, the monsoonal rain is continuing.

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This week is the thirtieth anniversary of Cyclone BOLA affecting New Zealand in March 1988. It hovered off to the north of NZ for three days when the moist eastly winds on its south side hammered our Gisborne coast. It was held there by a large HIGH east of NZ. It seemed to hold onto a Cyclone category according to the Saffir-Simpson scale until it got south to around 42S (As seen at Wiki Project TC tracks at en.wikipedia.org/wiki/Cyclone_Bola) ---- but really, as soon as it left the tropics it transited into a mid-latitude depression - We dropped the word "tropical" and kept referring to it as "Cyclone Bola" to help the broadcasting media deliver the severity of the weather forecast to those at the receiving end.
As seen at blog.metservice.com/Cyclone-Bola
I was one of the lead forecasters on duty at the time. I can remember that we allowed TV reporters to do live interviews from our forecast room, maybe for the first time?.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
The SPCZ is expected to strengthen this week and a pulse of convection is likely to travel southwards with that tropical low as it moves to Vanuatu and then Southeast to east of NZ.
However, the rain accumulation map at windy.com suggests that this pulse of convection may weaken a lot as it leaves the tropics.

Subtropical ridge (STR)
HIGH to east of NZ was unbudging last week but is moving is expected to move off to the east this week. It would have been interesting if that low from Vanuatu had formed last week--- its trip to the southeast would've been blocked and it may have taken a path like Bola. However, Bola had more moisture to start with.
Next HIGH is expected to form east of Tasmania on Tuesday and travel across southern NZ on Saturday and then weaken over the North Island on Sunday, helping to direct the low from the tropics harmlessly off to east of North Island.

Around Tasman Sea
Trough over the North Island on Monday. Front reaching the South Island on Monday is expected to be drawn to the northeast on Tuesday and deepen into a secondary Low northeast of North Island on Thursday and Friday. There may be strong winds around the south and west sides of that secondary low.

Panama to Galapagos /Marquesas
Looks Ok to depart Panama from Monday to Thursday this week, after that the voyage may encounter a longer than normal period of light winds from 80W to 110W, and it may be better to wait until mid-next-week.

Britian
The cold air that reached Britain last week had been dislodged from the Arctic circle by an freak heat wave in the Arctic circle. See www.thetimes.co.uk/article/beast-from-the-east-caused-by-freak-arctic-heatwave-h3krhw8r5
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If you would like more detail for your voyage, then check metbob.com to see what I offer.
Feedback to bob@metbob.com or txt 6427 7762212
I'm on Facebook at /www.facebook.com/metbobnz/
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com, Subscribe/unsubscribe at the bottom.
Or, if email wasn't from WordPress then send a reply email saying LEAVE.
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