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

04 June 2017

Bob Blog 4 June 2017

WEATHERGRAM
YOTREPS
Compiled Sun 04 June 2017

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.

Last month
Sea Surface temperature anomalies may be seen at www.ospo.noaa.gov/data/sst/anomaly/2017/anomnight.6.1.2017.gif
There continues to be more area covers by warm anomalies than by cool anomalies.
And now there is a warm river appearing along east coast of South America.

To see how the annual weather cycle and the seasons are working out, take a look at the average isobar maps for May compared with April using data from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

In May, the subtropical ridge in the southern hemisphere has travelled NORTHWARDS. This trend is subtle and doesn't show much in the isobars, but can be seen in the anomalies. There also seems to be a persistent trend for High pressure systems to linger around southern New Zealand, and this encourages southerly winds and cold fronts that herald them to often visit eastern New Zealand, a recipe for good winter alpine snow.
TRMM offers monthly rainfall maps at trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html
These show wetter than normal conditions over northern NZ. The heaviest rainfall last month was in spots from India to Papua New Guinea, also off the west coast of central America (Cyclone Adrian). Samoa had a wet month due to Cyclone Ella.

The Tropics
In my last blog, a week ago, Cyclone MORA was just forming. During the week MORA It brought a deluge to Sri Lanka and wind/rain damage to Bangladesh and Myanmar. The Sri Lanka rain marks a wet start to the 2017 Asian Monsoon, and a quick end to the 2017 Everest climbing season. More about Cyclone MORA from en.wikipedia.org/wiki/Cyclone_Mora

There are no cyclones or tropical depressions around tonight.

The last week's rain map (fromtrmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif)
shows a build-up of convection around Malaysia and Philippines, also across Papua new Guinea to Solomons /Vanuatu. This seems to be related to an MJO that is moving east, and may trigger tropical depressions in Micronesia in next few weeks.

Then again, models are picking this MJO to weaken the week.


WEATHER ZONES
SPCZ=South Pacific Convergence zone.
There is a convergence zone lingering between 5 and 10S from Tuvalu to Tokelau. Occasionally this zone affects Samoa, and Wallis/Futuna.
The main part of the SPCZ stretches from active-activity across Papua New Guinea and Solomons to quieter-activity south of Fiji and Tonga/Southern Cooks, where it merges into some jetstream cloud and the remains of an old cold front. All this is expected to travel north and east this week so that the SPCZ may reach Society islands of western FP this weekend.
Tropical accumulated rainfall for next week may be seen at windyty.com

Subtropical ridge (STR)
Next High departing Australia is likely to travel across the South Tasman Sea on Wednesday and then across Southern NZ on Thursday and Friday.

Australia to New Caledonia:
A Low is expected to form on the front in the South Tasman Sea on Monday. This Low should then travel northeast onto northern New Zealand by the weekend. This offers a period of W/SW wind son the back of this low good for getting from Australia to Noumea.
To catch these, you need to depart on Monday or Tuesday.

Departing NZ to the north for the tropics:
On Monday a small low is expected to cross the North Island. The SW winds that follow this on Tuesday offer the best opportunity for departure this week. They voyage is likely to encounter some NE winds and a passing front around Friday. If you wish to wait for the next opportunity, then that may be around middle of next week 13/14 June.

New Zealand (Northland) to the east (Tahiti)
After the Monday Low, there should be good departures to the east on Tuesday and Wednesday.

French Polynesia to the west (New):
There is an approaching SPCZ.
IF you depart this week aiming for Tonga then you will need to sail thru the SPCZ to get to Tonga, or IF you aim for Palmerston/Raro/Suwarrow, then will need to get across the light winds ahead of the approaching SPCZ.
For a voyage with good trade winds, wait for the SPCZ to fade or pass over Society Islands around Sat 10 June and then depart around 11 June.
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See my website http://www.metbob.com for more information
Feedback to bob@metbob.com or txt 6427 7762212
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
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