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

25 October 2015

BOB Blog 25 Oct

Bob Blog 25 Oct

WEATHERGRAM

YOTREPS

Issued 25 October 2015

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.

 

Tropical Note: A weekly treasure:

The Bureau of Meteorology Australia weekly tropical note at http://www.bom.gov.au/climate/tropical-note/ is updated every Tuesday and carries comments on the trends in the MJO oscillation.

Even if you are limited to only email via satphone or shortwave, you can read this note by sending an email to query@sailmail.com, no subject needed, saying SEND http://www.bom.gov.au/climate/tropical-note/

MJO stands for the Madden-Julian Oscillation, an increase in tropical convection that tends to travel eastwards from the Indian Ocean to the western parts of the South Pacific. It helps trigger the formation of Tropical cyclones. The MJO has been weak/ undetectable for many weeks, but is now starting to appear in the Indian Ocean. It usually takes around a month for it to track from there to South Pacific, so having an MJO in the Indian Ocean reduces the risk of a tropical cyclone forming in the South Pacific.

 

TROPICAL TOPICS

PATRICIA has come and gone, and was category 5 for a while off the west Mexican coast. OLAF is still in the mid North Pacific since last week.

And the many “Invest” areas in the Indian Ocean is associated with the MJO.

The Weekly rain maps at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif show increasing convection over western part of Indian Ocean, and a weakening of convection in the South Pacific.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to have a reasonably quiet week near Tuvalu and Tokelau, with scattered convection over Southern cooks/French Polynesia.

 

STR= Sub-tropical Ridge

The STR is weakening in the Tasman Sea area but is expected to stay strong to east of 180 this week. The squash zone of enhanced SE winds that is tonight between Niue and Austral Islands is expected to weaken from tomorrow.

High in northern Tasman Sea tonight is expected to cross northern NZ on over Tasmania tonight is expected to travel NE across Tasman Sea and cross northern NZ on Tuesday and then weaken.

Next HIGH is further south and is expected to travel around south end of Tasmania on Friday, and then slowly across northern NZ on Sun–Wed 1 to 4 Nov.

 

Over NZ/Tasman:

ACTIVE FRONT from Sydney to South Island on Monday and from off Coffs to central NZ on Tuesday is expected to deepen into a LOW between Lord Howe Island and North Island on Wednesday and this low is then expected to travel east across the North Island on Thursday with strong to gale SW winds and large swells on its western side. Avoid.

 

Travelling Tahiti to Marquesas.

It seems that several yachts are thinking of spending the cyclone season in Marquesas rather than Tahiti—seems sensible since this season is likely to be like 82/83 (14 cyclones, 10 in the Cook Islands/French Polynesia/Pitcairn area) or 97/98 (16 cyclones, 8 in French Polynesia).

The good news this week is that weather pattern is looking Ok for voyages from Tahiti and Marquesas for departures on local Monday or Tuesday, maybe Wednesday, with light winds between Tahiti and Tuamotu for motoring,  and then easterly winds between Tuamotu and Marquesas. This is a brief window, associated with a weak trough on the weak SPCZ over the Tahiti area next few days, and these windows are rare so go for it by Tuesday.

 

Travelling Tahiti to Tonga:

The SPCZ should stay north over most of this route and is weak over Tahiti, and the squash zone around Cooks Islands/Tahiti tonight should ease by local Tuesday, then there is a reasonable opportunity for departure. There are likely to be a few convergence zones along this route with some light winds.

 

The Island Cruising Association is holding the All Points rally to Opua and the Downunder rally from Noumea to Newcastle.

 

Between Tropics and NZ:

For the All Points Rally, ending in Opua:

A departure early this week should be Ok. It is likely to have a period of SW winds between 25 and 30 S with 2 to 3 metre swells on Thursday and Friday thanks to that NZ Low.

If you are heading for NZ from New Caledonia/Fiji or Tonga, then the main deciding pointers are the fronts crossing northern NZ. After that Low over NZ on Thursday 29 Oct, there is a slow-moving HIGH from Sun 1 to Wed

4 Nov and then a strong NW wind is expected (at this stage) over northern NZ around Thu 5 Nov, followed by a few days of westerly winds. Since there is nothing significant happening in-between the islands and NZ if you arrange a departure this week that avoids arriving in NZ on Thu 5 Nov,  then that should work—but seek updates as well as things keep changing.

 

Between Tropics and Australia

For the Downunder Rally (Noumea to Newcastle) A departure early this week should be Ok. It is likely to reach just moderate southerly winds and 2 m swells near 26S from that “Wed 28 Low”

between Lord Howe and NZ.

Newcastle is expected to have its next dose of strong winds on Monday 2 Nov, and since this voyage may usually take around 6-7 days, depart on Monday this week to try and arrive before these strong winds, or wait for an opportunity later this week, maybe Thursday onwards.

>>>>>>

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website http://www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com. Tell anyone you like that to subscribe they should email me.

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

Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.

To unsubscribe send a reply email saying LEAVE.

 

 

 

 

18 October 2015

Bob Blog 18 0ct 2015

WEATHERGRAM

YOTREPS

Issued 18 October 2015

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.

 

Bureau of Meteorology Australia have now issued their 1015-16 Tropical cyclone season outlook and they are going for a less active season.

See http://www.bom.gov.au/climate/ahead/tc.shtml

This ties in with the NIWA, MetService NZ and Fiji Met Service outlooks given here last week going for a more active season in our part of the South Pacific (east of 160E). Basically the activity is shifted eastwards by the El Nino episode we are having.

Now, since a lot of tropical Cyclone and Depression activity starts along the South Pacific Convergence Zone, it’s expected average position should show where most of this season’s tropical Cyclones are likely to form.

NIWA have published an  image showing this earlier this month as part of their Island Climate Update at

http://www.niwa.co.nz/island-climate-update-181-october-2015

and it shows the expected average position (green line) from now until December for the SPCZ from an ensemble of global climate models. The red line is the climate average for this time of year, showing how far north (and east) is this seasonal shift. In the image, brighter shades of purple show the expected wetter areas—showing that western Solomon Islands to Tonga are NOT expected to have much of a wet season this year.

Since many insurance companies define the South Pacific Cyclone Season as being from 1 November to 30 April (and remove their cover accordingly), a lot of yachts are likely to leave the warmth of Tonga /Fiji/New Caledonia and head for Australia/ New Zealand. (Small note: Minerva reef at 24S is technically OUT of the tropics, so even if your insurance cover may be void from 1 Nov in Tonga, it remains valid in Minerva forever!).

The Island Cruising Association is especially geared up to help those wishing to spend the cyclone season in NZ, and organise an ALL POINTS RALLY for this. It’s free (thanks to the sponsors) and helps yachts with weather info, resources and planning tools to try and make the passage as easy as possible. In Opua participants are offered a week of fun, entertainment and seminars, starting 16 Nov. It’s a bit late now, but if you want to sign up go to http://www.islandcruising.co.nz/?page_id=717

Australians do not want to be outdone and this year have started their own Noumea to Newcastle DOWNUNDER Cruisers Rally – an evolution of their Port2Port P2P Rally –and also an ICA event. Some have left already. Their Noumea Departure party is this Friday 23 Oct, and their week of fun and culture starts 15 Nov. If you want to know more about this then go to http://www.downunderrally.com/ and an entry form is at http://www.

islandcruising.co.nz/?page_id=3097.  I recommend the passage planning page by Rod Waterhouse at

http://www.downunderrally.com/#!passage-planning--weather-/c92m

To help these rallies I'll concentrate my Weathergram between now and mid- November on these events.

 

TROPICAL TOPICS

KOOPU has brought damaging wind and rain to Philippines and is now slowly working its way northwards along its west coast, and CHAMPI has also turned northwards already so may stay out at sea. While OLAF is this week’s cyclone for the mid North pacific.

During the past week we had an interesting tropical depression form north of Fiji, it went west then south and on Friday was on the verge of being named a tropical cyclone but didn't quite make the grade. It needs gale winds near its centre for at least half a circle.

It has made an interesting jump to the west on Sunday morning local time, as seen at the web site from Fiji Met Service at http://www.met.gov.fj/aifs_prods/65661.

html.

The Weekly rain maps at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif show strong rainfall near the Philippines from KOOPU and further east in CHAMPI, and also around Tuvalu.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ has lost some convective energy now that it has been take away by that tropical depression near Fiji. What is left is expected to have a reasonably quiet week neat Tuvalu and Samoa, with scattered convection over Southern cooks/French Polynesia,

 

STR= Sub-tropical Ridge

The STR is STRONG along around 30 to 35S, and has been creating squash zones of enhanced SE winds and/or southerly swell following fronts and on the northern side of the High cells as they migrate east.

High over Tasmania tonight is expected to travel NE across Tasman Sea and cross northern NZ on Tuesday and then migrate eastwards with a squash zone – mainly of 3m swells- on its north side particularly affecting the Tahiti to Niue route from Thursday to Saturday.

Another HIGH over Tasmania on Thursday is expected to reach northern NZ by Sunday 25 Oct, and then travel east and bring another squash zone to the Tahiti to Niue route next week.

 

Travelling Tahiti to Tonga:

A zone of 3m+ swells from the Southern Ocean affects southern part of this route on Tuesday and Wednesday UTC. Another zone of 3m+ swell, along with some strong SE winds, from a squash zone affects this route from Thursday to Saturday.

 

Between Tropics and NZ:

 

For the All Points Rally:

Early this week there are light winds near Fiji and rough seas off the south of New Caledonia—that may delay some starters.

If you are heading for NZ from New Caledonia/Fiji or Tonga, then the main deciding pointers are the fronts crossing northern NZ. There’s one this week on Thu/Fri 22/23 Oct, and its followed by a period of southerly quarter winds on Friday/Saturday—you should be able to cope with those by going W in southerly winds, SW in SE winds and SE in SW winds.

 

Between Tropics and Australia

For the Downunder Rally (Noumea to Newcastle) Some rough seas just south of New Caledonia and start of Tuesday so departure after that is more comfortable.

A southerly buster is forecast to reach Newcastle around midnight Wednesday and these southerlies may reach as far north as 25S on Wed/Thu maybe Friday, but should be able to be handled with appropriate waypoint diversions.

Strengthening northerly winds are likely offshore Newcastle on Monday and Tuesday 25-27 Oct and then a heat trough is expected to cross Newcastle on Wed 28 Oct possibly with thunderstorms.

AT this stage a Wednesday departure seems to be the most comfortable of the week.

>>>>>> 

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com. Tell anyone you like that to subscribe they should email me.

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

Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.

To unsubscribe send a reply email saying LEAVE.

 

 

11 October 2015

BOB BLOG 11 Oct

WEATHERGRAM

YOTREPS

Issued 11 October 2015

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.

 

A comparison of the Sea surface temperature anomaly map at start of October of this year with 1997 – as shown by NOAA may be  seen in the LA

Times:  LA Times link:

http://www.latimes.com/local/lanow/la-me-ln-massive-el-nino-is-now-too-

big-to-fail-scientist-says-20151009-story.html

Notice how this year there is an extension of cooler than normal sea from the Papua New Guinea to the Fiji Tonga area—whereas back in 1997 this

zone was warmer than normal.   It is reasonable to postulate (but hard to

prove in advance) that this finger of coolness may help reduce the risk of cyclone formation or cyclone support. A Mercator projection view of this cool blue finger-zone of reduced risk may be seen at  http://www.

ospo.noaa.gov/data/sst/anomaly/2015/anomp.10.8.2015.gif

 

Now that 1997/1998  South Pacific Cyclone season was the most active and longest on record with 16 named cyclones in the South Pacific basin between early October and early May. 

8 of these 16 affected French Polynesia Cook Islands

1982/83 was also an extreme El Nino year with 14 named cyclones:

10 of these 14 were in the French Polynesia/ Cook Islands area.

To compare El Nino seasons a good parameter to use is the NINO3.4, (based the sea surface temperature anomalies in the target area) and a long term graph of this may be found at https://besfeg.wordpress.

com/2015/05/27/will-a-big-el-nino-spell-doom-for-tropical-forests/

Data (up to Sep 2015) is from http://www.cpc.ncep.noaa.

gov/data/indices/sstoi.indices

 

The September 2015 value of the NINO3.4 anomaly was 2.28 compared with 1.

39 in September 198 and 2.21 in September 1997, so at first glance this is a match –and we can postulate (even if it may be difficult to prove in

advance) that the French Polynesia/Cook Islands area are at a higher risk than normal of being affected by tropical cyclones during this season.

However this is just one parameter and, as we can see for the opening image, there is more happening even in the SST anomaly map than just the

NINO3.4

 

Some web sites such as Wikipedia think that this cyclone season has already started, for they start their count from 1 July and RAQUEL formed

30 June, left the basin area and then re-entered on 4 July and faded the

next day.   However, I think that the vernal equinox, when the overhead

suns shifts into the southern Hemisphere, is a more logical date to start the count rather than from 1 July.

 

TROPICAL TOPICS

There is just one named storm in the tropics at present – NORA near Hawaii (again).

The Weekly rain maps  from http://trmm.gsfc.nasa.

gov/trmm_rain/Events/big_global_accumlation.gif show that convective activity has jumped in the past week from the Intertropical Convergence zone to the South Pacific Convergence zone.

This increased activity in the SPCZ coincided with a period of near equatorial westerly winds.

The tropical low on the north side of the equator near 10N 150E is expected to deepen further and may form a Tropical Cyclone.  The Low east of Solomon Islands is expected to weaken and move off to the SE.  SO the “twinning” mechanism seems to have missed working this time.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

There is a lot of activity between Eq. and 15S from 160E to 180 at present and this moisture is expected to feed along the SPCZ that extends

from eastern Solomon Islands to the Fiji area.   SO squally wind and rain

is likely to visit parts of Fiji around mid-week. The GFS model has a tropical low with this on Wednesday UTC but the more reliable EC model at www.tinyurl.com/ecaus has the low further west and from Sat 17 Oct—so the models are flip-flopping and the area is worth watching with care.

Strong SE winds on the south side of the SPCZ are expected to affect Fiji area until Wednesday, and then this zone of strong winds should shift south to around 25S and stay there for a few days.  The strong SE winds that have been affecting Vanuatu are expected to ease from Wednesday.

 

Further east a convergence zone of the north side of a passing front is expected to pass across French Polynesia over the next few days changing the wind direction over the south half of the area.

 

STR= Sub-tropical Ridge

High in the Northern Tasman sea on Sunday (HIGH1) is expected to stay there and fade away on Tuesday/Wednesday as a cold front travels north into it and across North Island and also fades. 

A new High, HIGH2,  following that cold front,  is expected to dominate the South Tasman Sea  by Wednesday and travel across Northern NZ on Friday to Saturday.

This pattern is expected to repeat with a front fading over northern NZ on Sunday 18 Oct and another High, HIGH3 form Monday 19 to Friday 23Oct.

HIGH2 is intense  enough to have a squash zone of strong SE winds on its northern side so that over New Caledonia, SE winds have eased over the weekend but are now expected to increase again from late Tuesday until Friday. And over Tonga, strong SE winds are expected from Wednesday to Saturday, and this squash zone should spread east to affect Niue/Southern Cooks/Society Islands.

 

Travelling Tahiti to Tonga or from Fiji to anywhere:

A difficult week, affected by SPCZ and a squash zone, so maybe stay put.

 

Between Tropics and NZ:

HIGHS 1, 2 and 3 dominate northern NZ over next two weeks, so winds are not strong, but the E/SE winds on the north side of the STR mean that trips from Tonga and New Caledonia have to start setting off with a leg to the SW and then turn to NZ around about 30S.

The weak “replacement” fronts between the highs on 13/14 Oct and 17/18 Oct and have NW winds ahead of them that offer good sailing breeze to northern NZ, but are followed by SW winds. 

As for southern NZ --- well, here be dragons:  vigorous disturbed westerly winds dominate proceedings.

>>>>>> 

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com. Tell anyone you like that to subscribe they should email me.

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

Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.

To unsubscribe send a reply email saying LEAVE.

 

 

04 October 2015

Bob Blog

WEATHERGRAM

YOTREPS

Issued 04 October 2015

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.

 

Tropics to NZ: - Strategy

  This is the time of year that yachts are staging themselves in Tonga (or Fiji or New Caledonia) and waiting for the right weather pattern for sailing to NZ or Australia.

 

In deciding upon a departure date, the first factor to consider is the local weather:  the South Pacific Convergence Zone SPCZ sometimes brings squalls, but is expected to stay north from Solomons to Tuvalu to Tokelau /Samoa to Northern Cooks this week.  It might visit Wallis and Futuna during middle of this week.  

 

Some like to use Minerva reef as an extra staging post since it is 1.5 days sail south of Tonga, and just out of the tropics (so marine insurance that is void in the tropics may work in Minerva).  But it only shelters you from the waves (so long as they don’t topple over the reef) and not from the wind. 

 

The second factor to watch are the HIGHS that travel along the Subtopic ridge STR, that zone between the trade winds of the tropics and the disturbed westerlies of the roaring 40s.  There is a HIGH in the Tasman Sea at present and it is expected to intensify on Tuesday, producing a SQUASH ZONE of enhanced trade winds on its northern side stretching from Coral Sea to Tonga.  During Wednesday this High is expected to weaken and the squash zone should retreat to the Coral Sea area by Thursday. Another HIGH is expected to travel from 45S over South Tasman Sea on Thursday to 30S over Northern Tasman Sea on Tue 13 Oct – this High is not expected to be intense enough to have a squash zone, but the strong SE winds are expected to remain in the Coral Sea. 

 

The third factor is to avoid strong southerly winds and heavy swells during the trip.  Good news is there isn’t much to report this week. There is a front moving off to east of NZ tonight followed by a SW/S flow, but it isn’t strong.  It may bring some SW swells from Southern Ocean to the area north of NZ but these have a lengthening period are reasonably flat. 

 

And you should try and time your trip so that it does not reach NZ with an active weather feature.  Since these voyages may take 8 to 10 days, the weather outlook that far out is not reliable on any weather models and things will change in the real world during the voyage.  However with resources such as windyty.com now available we can at least get an idea of the winds around NZ a week ahead.  Today’s data shows that a FRONT is likely to cross Northland around wed/Thu 14/15 Oct followed by a burst of southerly winds extending north of NZ to at least 30S.  SO avoid arriving in NZ then, and that means don’t depart Tonga late this week, unless you can beat that front or don’t mind encountering it.

  

This is the season that we sometimes get a procession of fronts travelling across Northern New Zealand, maybe 4 or 5 days apart. Not this week. When this pattern sets in, it may be necessary to deliberately time you departure to encounter one of these fronts near 30S (where they are usually weak) (and then dash for NZ in the SW winds that follow.  This strategy may require you to travel as far west as 170E before encountering the front, and that adds days to the journey if it is starting form Tonga.

 

A useful resource is www.yit.co.nz.  Patricia and David from Gulf Harbour Radio provide a method where by your position can be plotted on the web, and also provide daily weather updates via shortwave radio. You need to first register on this web site with your boat and crew details and then you simply email (send@yit.co.nz) or radio (call in to the sked) in your position and conditions in preferably each day.  These reports help me (and your loved ones) keep track of your progress.

David checks these reports and does a weather sked, Monday thru Saturday (NZ date), on 8752 at 1915UTC to make sure the models reflect your actual conditions.  He does a round-up of the weather in each island group, including passage weather, at 1930UTC. That’s 7.30am depending on your time zone.

 

The High seas forecast SUBTROPICS  is the official forecast for this area issued by the marine team at MetService is broadcast by Taupo Maritime Radio ZLM at 0903UTC on 6224 and 12356kHz , and 1003UTC on 9297 and 16531kHZ, then again on 2103UTC on 6224 and 12356kHz , and at 2203UTC on 9297 and 16531kHz.  If you have access to email on board then the text of this bulletin is available by sending an email to query@saildocs.com, no subject needed, with message SEND http://weather.noaa.gov/pub/data/raw/fq/fqps43.nzkl..txt

Or remember to email or TXT your position report to me at bob@metbob.com 64277762212

 

TROPICAL TOPICS From http://tropic.ssec.wisc.edu/

Tropical storm OHO is near Hawaii, Hurricane JOAQUIN is in the Atlantic, Typhoon MUJIGAE in in the China Sea, and Tropical Storm CHOI-WAN is in the NW Pacific 

The weekly rain maps as seen at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif show that rainfall in the South Pacific is confined to the SPCZ 

>>>>>> 

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage forecasts

– Feedback to bob@metbob.com. Tell anyone you like that to subscribe they should email me.

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

Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.

To unsubscribe send a reply email saying LEAVE.

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