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

30 August 2015

BobBlog 30 Aug

WEATHERGRAM

YOTREPS

Issued 30 August 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.

 

WESTWARD HO

Several yachts are currently in Tahiti and waiting for the right conditions to go west.

Over the past week or so an intense trough has been stationed west of Tahiti, blocking their way. Today this zone is weakening away over the Austral Islands -- that cloud which looks like a rope in the satellite imagery at http://www.meteo.pf/observation.php?carte=pfvdo is a whole line of squally showers, worth avoiding.

By Monday local this zone should have faded away and over the Society Islands there should be a wind change to southerly winds and clearing clouds. This is a good weather pattern for yachts to go west. Their next challenge is likely to be a weak trough/convergence zone near 165W on Friday 4 Sep local date, and at this stage this looks to be a weak trough.

 

Going west, there are three popular routes

1. The northern route: via Suwarrow and Samoa

2. The central route via Palmerston/Aitutaki

3. The southern route via Rarotonga/ Niue

 

1. Since we are having an El Nino, the South Pacific convergence zone SPCZ is spending more time than normal over the northern route, so that may be the squally way to go unless you can pick a period when the SPCZ is weaker than normal.

2. There can be occasional squash zones of enhanced trade winds over the central route. These are produced on the north side of any large HIGHS that travel east along the sub-tropical ridge about 30S. However the next few HIGHS are likely to be weaker than normal, so no squash zones are expected for the next few weeks.

3. The southern route is most at risk from the big swells that roll out of the southern ocean.

 

This week I think that often the central route may provide the least risk for adverse weather.

To help visualize the position of the SPCZ over the next week or so use the rain accumulation overlay option on windyty.com (found on the right) and select Next 10 days. The day-to-day variations of the SPCZ may be difficult to follow, but the 10-day accumulation shows its trend well.

 

TROPICAL TOPICS

The current cyclones can be seen at http://tropic.ssec.wisc.edu/ Things are quietening in the Asia and NW Pacific region, but very busy in the Hawaiian area, KILO continues from last week to west of Hawaii, IGNACIA is likely to pass off to the north of Hawaii on local Monday/Tuesday, and JIMENA may follow by the coming weekend. In the Atlantic, ERIKA left 20 people dead in Dominica and has now faded near Cuba before getting to Florida (but its remnants have brought some intense rain to Florida). And there is a developing storm in the eastern Atlantic.

The weekly rain maps at http://trmm.gsfc.nasa.

gov/trmm_rain/Events/big_global_accumlation.gif over the past two weeks show the intense rainfall from these tropical cyclones. Rain in the South Pacific has intensified since last week.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The south Pacific Convergence zone SPCZ extends from east of Solomon Islands across Rotuma to Samoa and then southeastwards. It has decreased in activity during the past week.

 

STR= Sub-tropical Ridge

The STR is the zone that divides the trade winds of the tropics from the disturbed westerly winds of the southern ocean. It is weak at present and north of its normal position.

The HIGH that is east of NZ is expected to travel east along 30 to 35S this week. It is NOT expected to have any appreciable squash zone son its northern side (between the High and the Trough on the SPCZ).

Another HIGH is expected to travel along 25S across the Northern Tasman Sea from Wednesday UTC, crossing Minerva reefs on Fri/Sat UTC. This HIGH is also NOT expected to have a squash zone.

 

NZ

A tale of woe/LOWS. LOW1 is expected to form off NW of NZ on Monday and travel slowly across the North Island on Tuesday and Wednesday. LOW2 has been bothering New South Wales since last Thursday and is The LOW that Trough is expected to finally waken into a trough crossing North Island on Wednesday. After a brief ridge on Friday LOW3 (crossing Sydney on

Thursday) is expected to cross the North Island on Sat/Sun 5/6 Sep. There is also a possibility of LOW4 over Northern NZ on 8/9 Sep.

>>>>>> 

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.

 

16 August 2015

Bob Blog 16 August

WEATHERGRAM
YOTREPS
Issued 16 August 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.
Rivers of wind, and puddles of calm:
The wind flow across an island gets distorted by the island itself as shown
in this image from Vitu Levu taken from Windyty.com last Wednesday, as shown
in my illustrated blog at
https://metbob.wordpress.com/2015/08/16/bob-blog-16-august/

SOI (the atmosphere)
The SOI (Southern Oscillation Index) measures the (normalized) air pressure
difference between Tahiti and Darwin. With Darwin having higher than
normal pressures, and the preponderance of Tahitian troughs, it is no
surprise that SOI has been so negative lately.
SOI is seen at
http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekl
y

TROPICAL TOPICS
GONI and ATSANI are in the western North Pacific and TD 11 is on west coast
of North America
The weekly rain maps over the past two weeks show the intense rainfall from
these tropical cyclones. There has been an easing in the monsoonal rain
over Thailand in the past week, and the rain in the South Pacific has eased
for a spell.
Weekly rain signature is seen at
http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is expected to weaken over South pacific this week, and remain from
east of
Solomon Islands to Tuvalu/Tokelau, with a branch that moves onto New
Caledonia on Tuesday and Wednesday.
The LOW that is south of French Polynesia mid-week has come from NZ, not
form the tropics. There is likely to be a weak trough on its northern side
and this is expected to reach Tahiti around Thursday UTC (Wednesday local).
Apart from these places mentioned above, this week looks OK for hopping from
Island to Island.

STR= Sub-tropical Ridge
The STR is the zone that divides the trade winds of the tropics from the
disturbed westerly winds of the southern ocean. This week it is mostly
north of its normal position and weaker than normal. However, a HIGH that
is expected to enter the Tasman Sea on Thursday should travel east along
30/35S across NZ on Fri/Sat and then to east of NZ early next week.

NZ
Trough is expected to cross NZ on Tuesday followed by a SW flow on
Wednesday, and then light winds from the next high for the remainder of the
week, turning northerly as the next trough approaches , due over North
island on Wednesday 26 August.
>>>>>> 
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.

09 August 2015

BOB BLOG 9 Aug

WEATHERGRAM

YOTREPS

Issued 9 August 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.

  

30 day actual and anomaly wind map may be seen at http://www.esrl.noaa.gov/psd/map/images/fnl/sfcwnd_30b.fnl.gif

This shows the wind anomalies for the last month to be typical of an El Nino cycle—with extra westerly winds along the Pacific Equator acting to move the sun-warmed sea to the east.  There are some quirks- the extra SW winds are over Chatham Islands rather than mainland NZ.  And that extra feed of air from Antarctica to the Aussie bight is interesting. 

 

El Nino in the ocean

Now that this El Nino is working in the atmosphere it is giving positive feedback to the heat that is being stored in the seas of the Eastern Equatorial Pacific.  This can be shown by looking at the sea-surface temperatures of the target areas, the NINO 3.4 index.   Over the past few weeks this has intensified.  It is now reaching levels last seen in 2010,  and has a long way to go to reach the extremes of 1998 (so don’t believe everything you may hear). 

 The Nino3.4 index since 1990s may be seen at http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=nino34&p=monthly

This current El Nino is expected to intensify until around November and then weaken, but it is not expected to drop below its current strength until around March 2016.

 

TROPICAL TOPICS

There are two tropical cyclones at present Hurricane/ Typhoon SOULDELOR has grown to become arguably the largest storm so far this year and is now inland over mainland China after crossing Taiwan.

To the north of SOULDELOR we have MOLAVE east of Japan  It seems that the Hawaiian area is getting sideswiped around once a week: This week we have Hurricane HILDA heading for the north side of Hawaii.

So far the North Atlantic is having a quiet summer—most of the activity is in the Pacific this year, possibly because of the warmer sea temperature.

 

The weekly rain maps over the past two weeks show the intense rainfall from these tropical cyclones, and even more intense and widespread rainfall in the monsoon over Myanmar, spreading across Thailand and towards Malaysia.

Weekly rain signatures for past two weeks may be seen at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

 

SPCZ=South Pacific Convergence zone.

Trough attached to SPCZ is tonight crossing Tonga and by Wednesday UTC (Tuesday local0 is expected to be weakening between Niue and Palmerston Islands. It has NE winds on its eastern side, some squalls with its main wind change, and is followed by southerly /SW winds.  It should continue east, reaching Tahiti on Saturday UTC (Friday local).

A trough/front from the Tasman Sea is expected to move onto New Caledonia on local Friday.

Try and pick your Island hopping to happen in-between these troughs.

 

STR= Sub-tropical Ridge

The weak ridge that is in the Tasman Sea tonight delivering a chilling southerly to NZ  is expected to travel across NZ on Tuesday and Wednesday, then further east along 30 to 45S east of NZ on Thu/Fri/Sat,  this is expected to be a frosty high.

 During this week a BFH, Big fat high, is expected to travel slowly across the interior of Australia, and finally enter the Tasman Sea early next week.

 

NZ

On Monday and Tuesday there are still a few disturbances in the southerly flow that may affect the east coast, but conditions look Ok for departing from Northland.

After a short period of light winds Wednesday morning, the northerly winds ahead of the next trough are expected over NZ by late Wednesday.

This trough is expected to start deepening into a LOW SE of Sydney on Wednesday night and then travel east crossing the Auckland area on Saturday night, and is expected to be squally and followed by a few days of squally W/SW winds until at least Mon 17 August. 

SO best days for anyone planning to go to the tropics are Monday and maybe Tuesday.

 

>>>>>> 

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 from WordPress: click the "unsubscribe" link on the bottom of the email. Or, if email wasn’t from WordPress then send a reply email saying LEAVE.

 

 

02 August 2015

BOB Blog 2 Aug

WEATHERGRAM

YOTREPS

Issued 2 August 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.

 

30 day anomaly map may be seen at http://www.esrl.noaa.gov/psd/map/images/fnl/slp_30a.fnl.anim.html

This shows that weather anomalies remained the same throughout July as they were in June, with a very strong sub-tropical ridge over Australia, Tasman Sea /NZ, and troughy conditions over Solomon Islands and Tahiti.  Lower than normal pressures across the North Pacific vaguely tie in with the large number of tropical depressions and cyclones there last month.

The 30 day anomaly map for 1 Aug shows not much of a signal over Asia, and indeed this year’s Asian monsoon has been progressing in a stuttering fashion.

Indian Monsoon index is seen at http://apdrc.soest.hawaii.edu/projects/monsoon/realtime-monidx.html

SOI (the atmosphere)

The SOI (Southern Oscillation Index) measures the (normalized) air pressure difference between Tahiti and Darwin.   With Darwin having higher than normal pressures, and the preponderance of Tahitian troughs, it is no surprise that SOI has been so negative lately.

SOI may be seen at http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekly

This current El Nino is expected to intensify until around November and then weaken, but it is not expected to drop below its current strength until around March 2016 , as shown at a figure from the International Research Institute (IRI) for Climate and Society (updated 14 July 2015).

TROPICAL TOPICS

There are two tropical cyclones at present GUILLERMO is Hurricane force and heading to affect northern part of Hawaii later this week; by then it is expected to weaken to storm force.

 And SOUDELOR is heading for Taiwan

The weekly rain maps over the past two weeks show the intense rainfall from these tropical cyclones, and even more intense and widespread rainfall from a tropical depression near east end of Solomons Islands.

Weekly rain signatures for past two weeks, may be seen at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

Depression to NW of Fiji is 01F and is expected to travel south between Fiji and Vanuatu then SSE to reach Kermadecs by Friday.  It may intensity on Monday and then weaken. It is worthwhile avoiding.  Associated trough should travel across Tonga on local Friday and early Saturday.

SPCZ this week is expected remain from Samoa to near the Tahiti area.  Moisture traveling along the SPCZ helped form a deep Low at 35S to south of French Polynesia over the last few days,  and this is expected to travel off to the east this week, and another Low is expected to form near 30S to south of French Polynesia later this week and travel off to the SE.

 

STR= Sub-tropical Ridge

The HIGH that was over northern NZ over the last few days has reduced to a ridge that extends to a High in the southern ocean and this ridge is expected to travel east along 30S this week to east of NZ.

Next high from Australia is not due in the Tasman Sea until Sat or Sunday 8/9 Aug.

NZ

One front is expected to cross South Island on Monday and North Island on Tuesday/Wednesday.  The next is expected to be more intense, connected to a Low below 980 hPa in the southern Ocean, and is expected to cross the South Island on Wednesday and the North Island on Thursday.  And then a cold and squally front associated with another low below 980 is expected to cross the South island on Friday and the North Island on Saturday.

Departing from Australia/NZ to the tropics this week:

>From Wednesday the swells over the Tasman Sea and to north of NZ are expected to be over 3 metres (and up to 6 or 7 metres) so it is more comfortable to stay put.

>>>>>> 

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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